201
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Glucocorticoid stress hormones and the effect of predation risk on elk reproduction. Proc Natl Acad Sci U S A 2009; 106:12388-93. [PMID: 19617549 DOI: 10.1073/pnas.0902235106] [Citation(s) in RCA: 160] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Predators affect prey demography through direct predation and through the costs of antipredator behavioral responses, or risk effects. Experiments have shown that risk effects can comprise a substantial proportion of a predator's total effect on prey dynamics, but we know little about their strength in wild populations, or the physiological mechanisms that mediate them. When wolves are present, elk alter their grouping patterns, vigilance, foraging behavior, habitat selection, and diet. These responses are associated with decreased progesterone levels, decreased calf production, and reduced population size [Creel S, Christianson D, Liley S, Winnie JA (2007) Science 315:960]. Two general mechanisms for the effect of predation risk on reproduction have been proposed: the predation stress hypothesis and the predator-sensitive-food hypothesis. Here, we used enzyme immunoassay to measure fecal glucocorticoid metabolite concentrations for 1,205 samples collected from 4 elk populations over 4 winters to test the hypothesis that the effect of predation risk on elk reproduction is mediated by chronic stress. Across populations and years, fecal glucocorticoid concentrations were not related to predator-prey ratios, progesterone concentrations or calf-cow ratios. Overall, the effect of wolf presence on elk reproduction is better explained by changes in foraging patterns that carry nutritional costs than by changes in glucocorticoid concentrations.
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202
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The roles of predator maturation delay and functional response in determining the periodicity of predator-prey cycles. Math Biosci 2009; 221:1-10. [PMID: 19563815 DOI: 10.1016/j.mbs.2009.06.004] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2008] [Revised: 06/03/2009] [Accepted: 06/21/2009] [Indexed: 11/22/2022]
Abstract
Population cycles in small mammals have attracted the attention of several generations of theoretical and experimental biologists and continue to generate controversy. Top-down and bottom-up trophic regulations are two recent competing hypotheses. The principal purpose of this paper is to explore the relative contributions of a variety of ecological factors to predator-prey population cycles. Here we suggest that for some species - collared lemmings, snowshoe hares and moose in particular - maturation delay of predators and the functional response of predation appear to be the primary determinants. Our study suggests that maturation delay alone almost completely determines the cycle period, whereas the functional response greatly affects its amplitude and even its existence. These results are obtained from sensitivity analysis of all parameters in a mathematical model of the lemming-stoat delayed system, which is an extension of Gilg's model. Our result may also explain why lemmings have a 4-year cycle whereas snowshoe hares have a 10-year cycle. Our parameterized model supports and extends May's assertion that time delay impacts cycle period and amplitude. Furthermore, if maturation periods of predators are too short or too long, or the functional response resembles Holling Type I, then population cycles do not appear; however, suitable intermediate predator maturation periods and suitable functional responses can generate population cycles for both prey and predators. These results seem to explain why some populations are cyclic whereas others are not. Finally, we find parameterizations of our model that generate a 38-year population cycle consistent with the putative cycles of the moose-wolf interactions on Isle Royale, Michigan.
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203
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Potts KB, Chapman CA, Lwanga JS. Floristic heterogeneity between forested sites in Kibale National Park, Uganda: insights into the fine-scale determinants of density in a large-bodied frugivorous primate. J Anim Ecol 2009; 78:1269-77. [PMID: 19523110 DOI: 10.1111/j.1365-2656.2009.01578.x] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
1. Despite a long history of research on the influence of fruit availability on the population density of large-bodied vertebrate frugivores, operational understanding of the factors regulating density in these taxa remains elusive. We propose that fruit resources can be distinguished from one another on the basis of their functional role for the animals in question, and that such a classification system can aid in identifying the most influential determinants of frugivore density. 2. We compared the availability of several resource classes between two sites in Kibale National Park, Uganda separated by only 12 km yet differing threefold in density of chimpanzees (Pan troglodytes). 3. We categorized plant species used for fruit by chimpanzees according to their availability relative to habitat-wide fruit productivity, and by their tendency towards inter-individual fruiting synchrony. We predicted that the site of high chimpanzee density would support a higher density of food plant species tending to produce crops during periods of high habitat-wide productivity [high fruit abundance (HFA foods)] and of those tending to fruit synchronously among individuals during times of low habitat-wide availability (sLFA foods). The first food class should provide chimpanzees with a high nutrient density (and thus promote population growth), whereas the second should provide stable subsistence during lean periods and thus a temporally consistent resource base. 4. Counter to our prediction, only sLFA resources were more abundant at the site of high chimpanzee density than at the site of low density. We suggest that sLFA resources are most important in influencing density of large-bodied frugivores.
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Affiliation(s)
- Kevin B Potts
- Yale University Department of Anthropology, New Haven, CT 06520, USA.
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204
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Sheriff MJ, Kuchel L, Boutin S, Humphries MM. Seasonal Metabolic Acclimatization in a Northern Population of Free-Ranging Snowshoe Hares,Lepus americanus. J Mammal 2009. [DOI: 10.1644/08-mamm-a-247r.1] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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205
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Karell P, Ahola K, Karstinen T, Zolei A, Brommer JE. Population dynamics in a cyclic environment: consequences of cyclic food abundance on tawny owl reproduction and survival. J Anim Ecol 2009; 78:1050-62. [PMID: 19493132 DOI: 10.1111/j.1365-2656.2009.01563.x] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
1. Understanding which factors regulate population dynamics may help us to understand how a population would respond to environmental change, and why some populations are declining. 2. In southern Finland, vole abundance shows a three-phased cycle of low, increase and decrease phases, but these have been fading out in recent years. During five such cycles (1981-1995), all tawny owls Strix aluco were censused in a 250-km(2) study area, and their reproduction and survival were monitored. 3. Males and females showed similar dynamics, but experienced breeders recruited more offspring and had higher survival than first breeders. Offspring recruitment, but not survival of breeding individuals varied in accordance with vole abundance. 4. The population's numerical response to prey abundance was primarily due to first-breeding individuals entering the population in the increase phase when immigration was the highest. First-breeding birds were younger, but experienced breeders were older in more favourable vole years. 5. A stage-specific matrix population model integrating survival and fecundity showed that, despite obvious variation in fecundity between vole cycle phases, this variation had limited importance for overall tawny owl population dynamics, but that the survival of experienced breeders during the low phase is most important for population growth. 6. Model and data agreed that the vole cycle drives the dynamics of this avian predator by limiting the recruitment of new breeders during the low phase. Population dynamics hence differ not only from the classic example of the species in a more temperate region in the UK where the number of territories is stable across years, but also from the dynamics of other avian vole predators in Fennoscandia where the recurring crash in vole abundance drastically lowers adult survival thereby creating vacancies.
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Affiliation(s)
- Patrik Karell
- Bird Ecology Unit, Department of Biological and Environmental Sciences, University of Helsinki, Finland.
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206
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Stephens CR, Heau JG, González C, Ibarra-Cerdeña CN, Sánchez-Cordero V, González-Salazar C. Using biotic interaction networks for prediction in biodiversity and emerging diseases. PLoS One 2009; 4:e5725. [PMID: 19478956 PMCID: PMC2685974 DOI: 10.1371/journal.pone.0005725] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2008] [Accepted: 11/20/2008] [Indexed: 11/19/2022] Open
Abstract
Networks offer a powerful tool for understanding and visualizing inter-species ecological and evolutionary interactions. Previously considered examples, such as trophic networks, are just representations of experimentally observed direct interactions. However, species interactions are so rich and complex it is not feasible to directly observe more than a small fraction. In this paper, using data mining techniques, we show how potential interactions can be inferred from geographic data, rather than by direct observation. An important application area for this methodology is that of emerging diseases, where, often, little is known about inter-species interactions, such as between vectors and reservoirs. Here, we show how using geographic data, biotic interaction networks that model statistical dependencies between species distributions can be used to infer and understand inter-species interactions. Furthermore, we show how such networks can be used to build prediction models. For example, for predicting the most important reservoirs of a disease, or the degree of disease risk associated with a geographical area. We illustrate the general methodology by considering an important emerging disease--Leishmaniasis. This data mining methodology allows for the use of geographic data to construct inferential biotic interaction networks which can then be used to build prediction models with a wide range of applications in ecology, biodiversity and emerging diseases.
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Affiliation(s)
- Christopher R Stephens
- Centro de Ciencias de la Complejidad, Universidad Nacional Autónoma de México, Ciudad de México, México.
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207
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Inchausti P, Ginzburg LR. Maternal effects mechanism of population cycling: a formidable competitor to the traditional predator-prey view. Philos Trans R Soc Lond B Biol Sci 2009; 364:1117-24. [PMID: 19324616 PMCID: PMC2666685 DOI: 10.1098/rstb.2008.0292] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
In the language of mathematics, one needs minimally two interacting variables (two dimensions) to describe repeatable periodic behaviour, and in the language of density dependence, one needs delayed, not immediate, density dependence to produce cyclicity. Neither language specifies the causal mechanism. There are two major potential mechanisms: exogenous mechanisms involving species interactions as in predator-prey or host-parasite, and endogenous mechanisms such as maternal effects where population growth results from the cross-generational transmission of individual quality. The species interactions view stemming from a major observation of Elton and a simultaneous independent theory by Lotka and Volterra is currently dominant. Most ecologists, when faced with cyclic phenomena, automatically look for an interacting species one step below or above in a food chain in order to find an explanation. Maternal effects hypothesis, verbally suggested in the 1950s, had only found its theoretical implementation in the 1990 s. In a relatively short time, the degree of acceptance of this view grew to the level of a 'minority opinion' as evidenced by the widely used textbook of Begon et al. This short review attempts to describe the arguments for and against this internal two-dimensional approach.
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Affiliation(s)
- Pablo Inchausti
- Centre d'Etudes Biologiques de Chizé (CNRS), 79360 Villiers-en-Bois, France
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208
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Plaistow SJ, Benton TG. The influence of context-dependent maternal effects on population dynamics: an experimental test. Philos Trans R Soc Lond B Biol Sci 2009; 364:1049-58. [PMID: 19324610 PMCID: PMC2666682 DOI: 10.1098/rstb.2008.0251] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Parental effects arise when either the maternal or paternal phenotype influences the phenotypes of subsequent generations. Simple analytical models assume maternal effects are a mechanism creating delayed density dependence. Such models predict that maternal effects can very easily lead to population cycles. Despite this, unambiguous maternal-effect mediated cycles have not been demonstrated in any system. Additionally, much evidence has arisen to invalidate the underlying assumption that there is a simple positive correlation between maternal performance and offspring performance. A key issue in understanding how maternal effects may affect population dynamics is determining how the expression of parental effects changes in different environments. In this study, we tested the hypothesis that maternal effects influence population dynamics in a context-dependent way. Populations of the soil mite, Sancassania berlesei, were set up at high density (500 eggs) or low density (50 eggs), with eggs that were either laid by young mothers or old mothers (a previously documented maternal effect in this system). The influence of maternal age on both population and egg and body-size dynamics was only observed in the populations initiated under low density rather than high density. This difference was attributable to the context-dependence of maternal effects at the individual level. In low-density (high food) conditions, maternal effects have an impact on offspring reproductive performance, creating an impact on the population growth rate. In high density (low food), maternal effects impact more on juvenile survival (not adult size or reproduction), creating a smaller impact on the population growth rate. This context dependence of effects at the population level means that, in fluctuating populations, maternal effects cause intermittent delayed density dependence that does not lead to persistent cycles.
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Affiliation(s)
- S J Plaistow
- School of Biological Sciences, University of Liverpool, Biosciences Building, Crown Street, Liverpool L69 7ZB, UK.
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209
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Abstract
We compute an accurate approximation to the probability of fixation for a beneficial mutation in a population fluctuating with a stationary distribution of population size. The population dynamics are described by the theta-logistic model with environmental variance, assuming that the population size is large enough to ignore demographic variance. We show that stochastic fluctuations of population size reduce the probability of fixation. However, it is not the magnitude of the population fluctuations per se that creates this reduction. Only the environmental variance has a substantial effect on the probability of fixation. The strength of density dependence (or expected return time to equilibrium) and the functional form of density-regulation, given by the parameter theta in the theta-logistic model, have little effect on the fixation probability. Effective population size based on harmonic mean population size will therefore underestimate the expected fixation rate of beneficial mutations in fluctuating populations.
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210
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Sheriff MJ, Krebs CJ, Boonstra R. The sensitive hare: sublethal effects of predator stress on reproduction in snowshoe hares. J Anim Ecol 2009; 78:1249-58. [PMID: 19426257 DOI: 10.1111/j.1365-2656.2009.01552.x] [Citation(s) in RCA: 294] [Impact Index Per Article: 19.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
1. Prey responses to high predation risk can be morphological or behavioural and ultimately come at the cost of survival, growth, body condition, or reproduction. These sub-lethal predator effects have been shown to be mediated by physiological stress. We tested the hypothesis that elevated glucocorticoid concentrations directly cause a decline in reproduction in individual free-ranging female snowshoe hares, Lepus americanus. We measured the cortisol concentration from each dam (using a faecal analysis enzyme immunoassay) and her reproductive output (litter size, offspring birth mass, offspring right hind foot (RHF) length) 30 h after birth. 2. In a natural monitoring study, we monitored hares during the first and second litter from the population peak (2006) to the second year of the decline (2008). We found that faecal cortisol metabolite (FCM) concentration in dams decreased 52% from the first to the second litter. From the first to the second litter, litter size increased 122%, offspring body mass increased 130%, and offspring RHF length increased 112%. Dam FCM concentrations were inversely related to litter size (r(2) = 0.19), to offspring birth mass (r(2) = 0.32), and to offspring RHF length (r(2) = 0.64). 3. In an experimental manipulation, we assigned wild-caught, pregnant hares to a control and a stressed group and held them in pens. Hares in the stressed group were exposed to a dog 1-2 min every other day before parturition to simulate high predation risk. At parturition, unsuccessful-stressed dams (those that failed to give birth to live young) and stressed dams had 837% and 214%, respectively, higher FCM concentrations than control dams. Of those females that gave birth, litter size was similar between control and stressed dams. However, offspring from stressed dams were 37% lighter and 16% smaller than offspring from control dams. Increasing FCM concentration in dams caused the decline of offspring body mass (r(2) = 0.57) and RHF (r(2) = 0.52). 4. This is the first study in a free-ranging population of mammals to show that elevated, predator-induced, glucocorticoid concentrations in individual dams caused a decline in their reproductive output measured both by number and quality of offspring. Thus, we provide evidence that any stressor, not just predation, which increases glucocorticoid concentrations will result in a decrease in reproductive output.
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Affiliation(s)
- Michael J Sheriff
- Centre for the Neurobiology of Stress, University of Toronto at Scarborough, 1265 Military Trail, Toronto, Ontario, Canada.
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211
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Environmental factors influencing adult sex ratio in Trinidadian guppies. Oecologia 2009; 159:735-45. [DOI: 10.1007/s00442-008-1257-x] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2008] [Accepted: 12/03/2008] [Indexed: 11/25/2022]
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212
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213
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Sergio F, Caro T, Brown D, Clucas B, Hunter J, Ketchum J, McHugh K, Hiraldo F. Top Predators as Conservation Tools: Ecological Rationale, Assumptions, and Efficacy. ANNUAL REVIEW OF ECOLOGY EVOLUTION AND SYSTEMATICS 2008. [DOI: 10.1146/annurev.ecolsys.39.110707.173545] [Citation(s) in RCA: 376] [Impact Index Per Article: 23.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Fabrizio Sergio
- Department of Applied Biology, Estación Biológica de Doñana, CSIC, 41013 Seville, Spain;
| | - Tim Caro
- Department of Wildlife, Fish & Conservation Biology, University of California, Davis, California 95616
| | - Danielle Brown
- Department of Wildlife, Fish & Conservation Biology, University of California, Davis, California 95616
| | - Barbara Clucas
- Department of Wildlife, Fish & Conservation Biology, University of California, Davis, California 95616
| | - Jennifer Hunter
- Department of Wildlife, Fish & Conservation Biology, University of California, Davis, California 95616
| | - James Ketchum
- Department of Wildlife, Fish & Conservation Biology, University of California, Davis, California 95616
| | - Katherine McHugh
- Department of Wildlife, Fish & Conservation Biology, University of California, Davis, California 95616
| | - Fernando Hiraldo
- Department of Applied Biology, Estación Biológica de Doñana, CSIC, 41013 Seville, Spain;
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214
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Sheriff MJ, Bosson CO, Krebs CJ, Boonstra R. A non-invasive technique for analyzing fecal cortisol metabolites in snowshoe hares (Lepus americanus). J Comp Physiol B 2008; 179:305-13. [PMID: 18998149 DOI: 10.1007/s00360-008-0314-4] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2008] [Revised: 09/30/2008] [Accepted: 10/11/2008] [Indexed: 10/21/2022]
Abstract
To develop non-invasive techniques for monitoring steroid stress hormones in the feces of free-living animals, extensive knowledge of their metabolism and excretion is essential. Here, we conducted four studies to validate the use of an enzyme immunoassay for monitoring fecal cortisol metabolites in snowshoe hares (Lepus americanus). First, we injected 11 hares with radioactive cortisol and collected all voided urine and feces for 4 days. Radioactive metabolites were recovered predominantly in the urine (59%), with only 8% recovered in the feces. Peak radioactivity was detected an average of 3.5 and 5.7 h after injection in the urine and feces, respectively. Second, we investigated diurnal rhythms in fecal cortisol metabolites by measuring recovered radioactivity 2 days after the radioactive cortisol injection. The total amount of radioactivity recovered showed a strong diurnal rhythm, but the amount of radioactivity excreted per gram of feces did not, remaining constant. Third, we injected hares with dexamethasone to suppress fecal cortisol metabolites and 2 days later with adrenocorticotropic hormone to increase fecal cortisol metabolites. Dexamethasone decreased fecal cortisol metabolites concentrations by 61% and adrenocorticotropic hormone increased them by 1,000%, 8-12 h after injection. Fourth, we exposed hares to a simulated predator (dog). This increased the fecal cortisol metabolites concentrations by 175% compared with baseline concentrations 8-12 h after exposure. Thus, this enzyme immunoassay provides a robust foundation for non-invasive field studies of stress in hares.
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Affiliation(s)
- Michael J Sheriff
- Department of Zoology, University of British Columbia, Vancouver, BC, Canada.
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215
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216
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Predicting synergistic effects of resources and predators on foraging decisions by juvenile Steller sea lions. Oecologia 2008; 158:775-86. [DOI: 10.1007/s00442-008-1189-5] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2008] [Accepted: 10/01/2008] [Indexed: 10/21/2022]
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217
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Bartel RA, Knowlton FF, Stoddart LC. Long-term Patterns in Mammalian Abundance in Northern Portions of the Great Basin. J Mammal 2008. [DOI: 10.1644/07-mamm-a-378.1] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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218
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Peckarsky BL, Abrams PA, Bolnick DI, Dill LM, Grabowski JH, Luttbeg B, Orrock JL, Peacor SD, Preisser EL, Schmitz OJ, Trussell GC. REVISITING THE CLASSICS: CONSIDERING NONCONSUMPTIVE EFFECTS IN TEXTBOOK EXAMPLES OF PREDATOR–PREY INTERACTIONS. Ecology 2008; 89:2416-25. [PMID: 18831163 DOI: 10.1890/07-1131.1] [Citation(s) in RCA: 264] [Impact Index Per Article: 16.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Affiliation(s)
- Barbara L Peckarsky
- Department of Zoology, 453 Birge Hall, University of Wisconsin, Madison, Wisconsin 53706, USA.
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219
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Affiliation(s)
- T C R White
- School of Agriculture Food and Wine, Waite Agricultural Research Institute, The University of Adelaide, Glen Osmond, South Australia 5064, Australia.
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220
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Voles on small islands: effects of food limitation and alien predation. Oecologia 2008; 157:419-28. [DOI: 10.1007/s00442-008-1084-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2008] [Accepted: 05/23/2008] [Indexed: 10/21/2022]
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221
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Reid JM, Bignal EM, Bignal S, Mccracken DI, Bogdanova MI, Monaghan P. Investigating patterns and processes of demographic variation: environmental correlates of pre-breeding survival in red-billed choughs Pyrrhocorax pyrrhocorax. J Anim Ecol 2008; 77:777-88. [DOI: 10.1111/j.1365-2656.2008.01400.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
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222
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Affiliation(s)
- Richard S Ostfeld
- Cary Institute of Ecosystem Studies, PO Box AB, 65 Sharon Turnpike, Millbrook, New York 12545, USA.
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223
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Creel S, Christianson D. Relationships between direct predation and risk effects. Trends Ecol Evol 2008; 23:194-201. [PMID: 18308423 DOI: 10.1016/j.tree.2007.12.004] [Citation(s) in RCA: 520] [Impact Index Per Article: 32.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2007] [Revised: 12/06/2007] [Accepted: 12/10/2007] [Indexed: 11/29/2022]
Abstract
Risk effects arise when prey alter their behavior in response to predators, and these responses carry costs. Empirical studies have found that risk effects can be large. Nonetheless, studies of predation in vertebrate conservation and management usually consider only direct predation. Given the ubiquity and strength of behavioral responses to predators by vertebrate prey, it is not safe to assume that risk effects on dynamics can be ignored. Risk effects can be larger than direct effects. Risk effects can exist even when the direct rate of predation is zero. Risk effects and direct effects do not necessarily change in parallel. When risk effects reduce reproduction rather than survival, they are easily mistaken for limitation by food supply.
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Affiliation(s)
- Scott Creel
- Department of Ecology, Montana State University, Bozeman, MT 59717, USA.
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224
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Aunapuu M, Dahlgren J, Oksanen T, Grellmann D, Oksanen L, Olofsson J, Rammul U, Schneider M, Johansen B, Hygen HO. Spatial Patterns and Dynamic Responses of Arctic Food Webs Corroborate the Exploitation Ecosystems Hypothesis (EEH). Am Nat 2008; 171:249-62. [PMID: 18197777 DOI: 10.1086/524951] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Affiliation(s)
- Maano Aunapuu
- Department of Ecology and Environmental Science, Umeå University, SE-90187 Umeå, Sweden.
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225
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Chapter 25 Contrasting Wolf–Ungulate Interactions in the Greater Yellowstone Ecosystem. ACTA ACUST UNITED AC 2008. [DOI: 10.1016/s1936-7961(08)00225-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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226
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Newey S, Dahl F, Willebrand T, Thirgood S. Unstable dynamics and population limitation in mountain hares. Biol Rev Camb Philos Soc 2007; 82:527-49. [PMID: 17944616 DOI: 10.1111/j.1469-185x.2007.00022.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
The regular large-scale population fluctuations that characterize many species of northern vertebrates have fascinated ecologists since the time of Charles Elton. There is still, however, no clear consensus on what drives these fluctuations. Throughout their circumpolar distribution, mountain hares Lepus timidus show regular and at times dramatic changes in density. There are distinct differences in the nature, amplitude and periodicity of these fluctuations between regions and the reasons for these population fluctuations and the geographic differences remain largely unknown. In this review we synthesize knowledge on the factors that limit or regulate mountain hare populations across their range in an attempt to identify the drivers of unstable dynamics. Current knowledge of mountain hare population dynamics indicates that trophic interactions--either predator-prey or host-parasite--appear to be the major factor limiting populations and these interactions may contribute to the observed unstable dynamics. There is correlative and experimental evidence that some mountain hare populations in Fennoscandia are limited by predation and that predation may link hare and grouse cycles to microtine cycles. Predation is unlikely to be important in mountain hare populations in Scotland as most hares occur on sporting estates where predators are controlled, but this hypothesis remains to be experimentally tested. There is, however, emerging experimental evidence that some Scottish mountain hare populations are limited by parasites and that host-parasite interactions contribute to unstable dynamics. By contrast, there is little evidence from Fennoscandia that parasitism is of any importance to mountain hare population dynamics, although disease may cause periodic declines. Although severe weather and food limitation may interact to cause periodic high winter mortality there is little evidence that food availability limits mountain hare populations. There is a paucity of information concerning the factors limiting or regulating mountain hare populations in the Alps of Central Europe or in the tundra and taiga belts of Russia. Future research on mountain hare population dynamics should focus on the interactions between predation, parasitism and nutrition with stochastic factors such as climate and anthropogenic management including harvesting.
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Affiliation(s)
- Scott Newey
- Department of Animal Ecology, Swedish University of Agricultural Sciences, S-901 83 Umeå, Sweden.
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227
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Pedersen AB, Greives TJ. The interaction of parasites and resources cause crashes in a wild mouse population. J Anim Ecol 2007; 77:370-7. [PMID: 18028357 DOI: 10.1111/j.1365-2656.2007.01321.x] [Citation(s) in RCA: 170] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
1. Populations of white-footed mice Peromyscus leucopus and deer mice Peromyscus maniculatus increase dramatically in response to food availability from oak acorn masts. These populations subsequently decline following this resource pulse, but these crashes cannot be explained solely by resource depletion, as food resources are still available as population crashes begin. 2. We hypothesized that intestinal parasites contribute to these post-mast crashes; Peromyscus are infected by many intestinal parasites that are often transmitted by density-dependent contact and can cause harm to their hosts. To test our hypothesis, we conducted a factorial experiment in natural populations by supplementing food to mimic a mast and by removal of intestinal nematodes with the drug, ivermectin. 3. Both food supplementation and the removal of intestinal nematodes lessened the rate and magnitude of the seasonal population declines as compared with control populations. However, the combination of food supplementation and removal of intestinal nematodes prevented seasonal population crashes entirely. 4. We also showed a direct effect on the condition of individuals. Faecal corticosterone levels, an indicator of the stress response, were significantly reduced in populations receiving both food supplementation and removal of intestinal nematodes. This effect was observed in autumn, before the overwinter crash observed in control populations, which may indicate that stress caused by the combination of food limitation and parasite infection is a physiological signal that predicts low winter survival and reproduction. 5. This study is one of the few to demonstrate that the interaction between resource availability and infectious disease is important for shaping host population dynamics and emphasizes that multiple factors may drive oscillations in wild animal populations.
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Affiliation(s)
- Amy B Pedersen
- Department of Biology, University of Virginia, Charlottesville, VA 22904, USA.
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228
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Hughes AR, Byrnes JE, Kimbro DL, Stachowicz JJ. Reciprocal relationships and potential feedbacks between biodiversity and disturbance. Ecol Lett 2007; 10:849-64. [PMID: 17663718 DOI: 10.1111/j.1461-0248.2007.01075.x] [Citation(s) in RCA: 89] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Two major foci of ecological research involve reciprocal views of the relationship between biodiversity and disturbance: disturbance determines community diversity or diversity determines realized disturbance severity. Here, we present an initial attempt to synthesize these two approaches in order to understand whether feedbacks occur, and what their effects on patterns of diversity might be. Our review of published experiments shows that (i) disturbance severity can be both a cause and a consequence of local diversity in a wide range of ecosystems and (ii) shapes of the unidirectional relationships between diversity and disturbance can be quite variable. To explore how feedbacks between diversity and disturbance might operate to alter expected patterns of diversity in nature, we develop and then evaluate a conceptual model that decomposes the relationships into component parts, considering sequentially the effect of diversity on disturbance severity, and the effect of realized disturbance on diversity loss, subsequent recruitment, and competitive exclusion. Our model suggests that feedbacks can increase mean values of richness, decrease variability, and alter the patterns of correlation between diversity and disturbance in nature. We close by offering ideas for future research to help fill gaps in our understanding of reciprocal relationships among ecological variables like diversity and disturbance.
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Affiliation(s)
- A Randall Hughes
- Evolution and Ecology, University of California-Davis, One Shields Avenue, Davis, CA 95616, USA.
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229
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Kerlin DH, Haydon DT, Miller D, Aebischer NJ, Adam Smith A, Thirgood SJ. Spatial synchrony in red grouse population dynamics. OIKOS 2007. [DOI: 10.1111/j.2007.0030-1299.16145.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
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230
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Newey S, Willebrand T, Haydon DT, Dahl F, Aebischer NJ, Smith AA, Thirgood SJ. Do mountain hare populations cycle? OIKOS 2007. [DOI: 10.1111/j.0030-1299.2007.15868.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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231
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Rammul Ü, Oksanen T, Oksanen L, Lehtelä J, Virtanen R, Olofsson J, Strengbom J, Rammul I, Ericson L. Vole-vegetation interactions in an experimental, enemy free taiga floor system. OIKOS 2007. [DOI: 10.1111/j.0030-1299.2007.14981.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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232
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233
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Hodges KE, Boonstra R, Krebs CJ. Overwinter mass loss of snowshoe hares in the Yukon: starvation, stress, adaptation or artefact? J Anim Ecol 2007; 75:1-13. [PMID: 16903038 DOI: 10.1111/j.1365-2656.2005.01018.x] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
1. Overwinter mass loss can reduce energetic requirements in mammals (Dehnel's phenomenon). Alternatively, mass loss can result from food limitation or high predation risk. 2. We use data from fertilizer, food-supplementation and predator-exclusion experiments in the Yukon during a population cycle from 1986 to 1996 to test the causes of overwinter mass loss by snowshoe hares (Lepus americanus). In all years, some hares on control sites gained mass overwinter. During the increase phase the majority gained mass, but in all other phases the majority lost mass. 3. Snowshoe hares weighing <1000 g in autumn always gained mass overwinter, as did the majority that weighed 1000-1400 g. Hares weighing >1800 g in autumn usually lost mass. 4. Snowshoe hares on the predator-exclosure + food site gained mass overwinter in all years. Hares on the food-supplementation sites lost mass during the decline but gained mass in all other phases. Fertilization had little effect on mass dynamics. 5. Snowshoe hares were more likely to lose mass during winters with low survival rates. Snowshoe hares on the predator-exclosure treatments were more likely to gain mass than were hares on control sites. 6. Overwinter mass loss was correlated with maximum snow depth. At equivalent snow depths, hares on food-supplemented areas lost 98 g (+/- 14.6 SE) less on average than hares on the controls and predator-exclosure treatment. 7. Bone-marrow fat was related to body mass and cause of death. Small hares had the lowest marrow fat. Hares killed by humans had higher marrow fat than those killed by predators; hares that simply died had the lowest marrow fat. Hares on food-supplemented sites had the highest kidney and marrow fat. 8. Overwinter-mass loss for snowshoe hares is explained interactively by winter conditions, food supply, predation risk and autumn mass. Some snowshoe hares lost mass overwinter in all years and on all treatments, suggesting that reducing body mass may facilitate survival, especially in cases where foraging costs are high energetically or increase predation risk.
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Affiliation(s)
- Karen E Hodges
- Department of Zoology, University of British Columbia, 6270 University Blvd, Vancouver, BC V6T 1Z4, Canada.
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234
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Massey FP, Ennos AR, Hartley SE. Herbivore specific induction of silica-based plant defences. Oecologia 2007; 152:677-83. [PMID: 17375331 DOI: 10.1007/s00442-007-0703-5] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2006] [Accepted: 02/22/2007] [Indexed: 11/29/2022]
Abstract
Induced plant responses to herbivory have major impacts on herbivore feeding behaviour, performance and population dynamics. These effects are well established for chemical defences, but induction of physical defences remains far less studied. However, for many plants, it is physical defences that play the major role in regulating the levels of herbivore damage sustained. We provide evidence that, in grasses, induction of physical defences is both specific to herbivore feeding, as opposed to mechanical damage, and may be dependant on the amount of damage imposed. Furthermore, we show that the magnitude of the induction response is sufficient to deter further damage and affect herbivore performance. We compared silica induction in two grass species in response to vertebrate and invertebrate damage, and to mechanical defoliation. Induction was assessed at two levels of damage over 16 months. Foliar silica content did not increase in response to mechanical defoliation, but damage by either voles or locusts resulted in increases in silica content of over 400%. This increase deterred feeding by both voles and locusts. Silica induction in grasses due to repeated damage events over a prolonged period suggests a possible role for silica defence in the cyclical population fluctuations observed in many grass-feeding herbivores.
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Affiliation(s)
- Fergus P Massey
- Department of Biology and Environmental Science, University of Sussex, Falmer, Brighton, East Sussex, BN1 9QG, UK.
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235
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Wirsing A, Murray D. Food supplementation experiments revisited: verifying that supplemental food is used by its intended recipients. CAN J ZOOL 2007. [DOI: 10.1139/z07-048] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Field-based food supplementation experiments can determine whether populations are limited by natural food availability. However, they may yield spurious results if added food is hoarded by dominants, exploited by immigrants, or delivered ineffectively. Surprisingly, population-level approaches accounting for these potential sources of bias have not been established. We explored responses of free-ranging snowshoe hares ( Lepus americanus Erxleben, 1777) to food supplementation by contrasting per capita browsing rates on three study sites with added food with those on three control sites during two winters. Food augmentation reduced foraging pressure by hares; this reduction was significant when browse species of high dietary importance were considered. By implication, hares on manipulated sites switched from favored natural foods to supplemental food, meaning that the extra food found its mark and was not heavily exploited by immigrants or hoarded by dominants. Demographic responses to food addition were not detected on the manipulated sites, indicating that the study population was not food limited. Given the success with which we detected the signal of supplementation and eliminated potential confounding factors, we suggest that future studies using food addition in the context of herbivore population dynamics would benefit from a more mechanistic approach; this may involve measurement of browsing rates on manipulated and control sites.
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Affiliation(s)
- A.J. Wirsing
- Department of Biological Sciences, Simon Fraser University, Burnaby, BC V5A 1S6, Canada
- Department of Biology, Trent University, Peterborough, ON K9J 7B8, Canada
| | - D.L. Murray
- Department of Biological Sciences, Simon Fraser University, Burnaby, BC V5A 1S6, Canada
- Department of Biology, Trent University, Peterborough, ON K9J 7B8, Canada
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236
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Olsson J, Svanbäck R, Eklöv P. Effects of resource level and habitat type on behavioral and morphological plasticity in Eurasian perch. Oecologia 2007; 152:48-56. [PMID: 17431684 DOI: 10.1007/s00442-006-0588-8] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2006] [Accepted: 10/11/2006] [Indexed: 11/29/2022]
Abstract
Spatial and temporal heterogeneity in the environment is a common feature affecting many natural populations. For example, both the resource levels and optimal habitat choices of individuals likely change over time. One way for organisms to cope with environmental variation is to display adaptive plasticity in traits such as behavior and morphology. Since trait plasticity is hypothesized to be a prerequisite for character divergence, studies of mechanisms behind such plasticity are warranted. In this study, we looked at the interaction of two potentially important environmental variables on behavioral and morphological plasticity in Eurasian perch (Perca fluviatilis L.). More specifically, the plastic responses in activity and morphology of perch exposed to different resource levels and simulated habitat types were studied in an aquarium experiment. The resource level experienced had a large influence on plasticity in both activity and morphology. Behavioral adaptations have been thought to mediate morphological transitions, and we suggest that the morphological response to the resource level was mediated by differences in activity and growth rates. The habitat type also affected morphological plasticity but to a lesser extent, and there was no effect on activity from habitat type. Based on these results, we suggest that it is essential to include several environmental factors acting in concert when studying mechanisms behind trait plasticity. We also propose that variation in resource levels might play a key role in fostering trait plasticity in at least fish populations, while other environmental variables such as divergent habitat complexities and prey types might be less influential. Dynamics in resource levels and optimal habitat choices might thus be important factors influencing character divergence in natural populations.
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Affiliation(s)
- Jens Olsson
- Limnology/Department of Ecology and Evolution, Evolutionary Biology Centre, Uppsala University, Norbyv. 20, 752 36 Uppsala, Sweden.
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237
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Abstract
AbstractThe impact of parasites on domestic livestock is well known. It is also clear that parasites have the potential to reduce reproductive success and survival at the individual level in wild animal populations (often through effects on body condition). However, the degree to which these impacts can regulate populations is difficult to determine because of the logistics of conducting the necessary experimental manipulations of either hosts or parasites. In addition, the relative importance of this mechanism compared to other regulatory factors such as predation and competition for food resources has not been quantified. Studies that have investigated the impact of parasites on wild mammals are reviewed and the merits of cross-sectional sampling and experimental approaches are presented. Finally, evidence for parasite mediated population regulation in wild mammals is examined and the need to develop experimental approaches that address this mechanism and its interaction with other regulatory processes is discussed.
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238
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LINDSTRÖM JAN, RANTA ESA, KOKKO HANNA, LUNDBERG PER, KAITALA VEIJO. From arctic lemmings to adaptive dynamics: Charles Elton's legacy in population ecology. Biol Rev Camb Philos Soc 2007. [DOI: 10.1111/j.1469-185x.2000.tb00061.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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239
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Kennedy P, Bruns T. Mycorrhizas take root at the Ecological Society of America. THE NEW PHYTOLOGIST 2007; 176:745-748. [PMID: 17997760 DOI: 10.1111/j.1469-8137.2007.02280.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Affiliation(s)
- Peter Kennedy
- Department of Biology, Lewis and Clark College, 0615 SW Palatine Hill Road, Portland, OR 97219, USA
| | - Tom Bruns
- Department of Plant and Microbial Biology, 321 Koshland Hall, University of California, Berkeley, CA 94720, USA
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240
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Boonstra R, Krebs CJ. Population limitation of the northern red-backed vole in the boreal forests of northern Canada. J Anim Ecol 2006; 75:1269-84. [PMID: 17032359 DOI: 10.1111/j.1365-2656.2006.01149.x] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
1. Across the vast boreal forests of North America, no population cycles in Clethrionomys species occur. In Eurasia, by contrast, some Clethrionomys populations of the same species undergo regular 3-5-year cycles. We examined the effects of nutrients, food, competitors, predators and climate on population limitation in the northern red-backed vole (Clethrionomys rutilus Pallas) in the south-western Yukon to determine why this difference occurs. 2. From 1986 to 1996 we added food, reduced large mammal predators and excluded snowshoe hares (Lepus americanus Erxleben) from large plots and found that none of these manipulations affected red-backed vole abundance. Adding nutrients as nitrogen, phosphorus and potassium (NPK) fertilizer had a slight negative effect, probably acting through a reduction in dwarf shrub productivity caused by competition from grasses. 3. We monitored weasel populations directly through trapping and indirectly through snow tracking. Predation by these vole specialists was irrelevant as a limiting factor most of the time because voles in this area do not reach the densities needed to sustain weasel populations. Other boreal forest mammal and bird predators did not focus on red-backed voles. However, when red-backed vole populations increased in the forest and Microtus voles also increased in the meadows, weasel populations increased and may have temporarily depressed red-backed voles in winter. 4. We monitored one major potential food, white spruce seeds, but seed fall was not related to population changes in red-backed voles, even after mast years. 5. We assessed the impact of weather variables, and the average depth of the snow pack during winter (October-March) was correlated directly with vole demography, having both direct effects in that year and delayed effects in the following year. 6. Our long-term trapping data (1973-96) indicate that Clethrionomys populations fluctuated, with peaks following hare peaks by 2-3 years. 7. We propose that the key variable limiting these vole populations is overwinter survival, and this is a function of overwinter food from berries produced during the previous summer by dwarf shrubs. These shrubs may be stimulated by abundant moisture from winter snows or by periodic fertilization from large quantities of pellets produced at snowshoe hare peaks.
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Affiliation(s)
- Rudy Boonstra
- Centre for the Neurobiology of Stress, Department of Life Sciences, University of Toronto at Scarborough, 1265 Military Trail, Scarborough, ONT, M1C 1A4, Canada.
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241
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Abstract
Although the possibility that food and predators may interact in limiting avian populations has long been recognized, there have been few attempts to test this experimentally in the field. We conducted a manipulative food addition experiment on the demography of Song Sparrows (Melospiza melodia) across sites that varied in predator abundance, near Victoria, British Columbia, Canada, over three consecutive breeding seasons. We previously showed that food and predators had interactive effects on annual reproductive success (young fledged per female). Here, we report the effects on egg production. Our results show that food limits the total number of eggs laid over the breeding season ("total egg production") and that interactive food and predator effects, including food effects on nest predation, determine how those eggs are "parceled out" into different nests. Food addition alone significantly affected total egg production, and there was no significant interannual variability in this result. At the same time, both food and predators affected the two determinants of total egg production: "clutch number" (total number of clutches laid) and average clutch size. Both clutch number and size were affected by a food x predator x year interaction. Clutch number was lower at low-predator locations because there was less nest predation and thus less renesting. Food addition also significantly reduced nest predation, but there was significant interannual variation in this effect. This interannual variation was responsible for the food x predator x year interactions because the larger the effect of food on nest predation in a given year, the smaller was the effect of food on clutch number; and the smaller the effect of food on clutch number, the larger was the effect of food on clutch size. Potential predator and year effects on total egg production were thus cancelled out by an inverse relationship between clutch number and clutch size. We suggest that combined food and predator effects on demography could be the norm in both birds and mammals.
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Affiliation(s)
- Liana Zanette
- Department of Biology, University of Western Ontario, London, Ontario N6A 5B7, Canada.
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242
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Gonzalez-Andujar JL, Fernandez-Quintanilla C, Navarrete L. Population Cycles Produced by Delayed Density Dependence in an Annual Plant. Am Nat 2006; 168:318-22. [PMID: 16947107 DOI: 10.1086/506915] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2005] [Accepted: 04/12/2006] [Indexed: 11/03/2022]
Abstract
In contrast to insect and animal populations, little attention has been directed to the study of cycles in plant populations. It has been argued on theoretical grounds that plants present stable dynamics. Nevertheless, there are examples where plant populations appear to exhibit oscillatory dynamics, but the oscillatory signal is variable and comes from very short time series data. Using a combination of time series, models, and empirical results, we present evidence of population cycles for Descurania sophia in a 16-year field experiment. Endogenous and exogenous causal mechanisms were studied to identify processes underlying this temporal dynamic. Our results show a 4-year cycle produced by delayed density dependence. We suggest that high nutrient levels might be responsible for the observed dynamics of D. sophia. Our results suggest that although plant population dynamics may be stabilized by direct density dependence, delayed density dependence could destabilize dynamics.
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Affiliation(s)
- J L Gonzalez-Andujar
- Departamento Protección de Cultivos, Instituto de Agricultura Sostenible (Consejo Superior de Investigaciones Científicas), Apartado 4084, 14080 Córdoba, Spain.
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243
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Austin D, Bowen WD, McMillan JI, Boness DJ. Stomach temperature telemetry reveals temporal patterns of foraging success in a free-ranging marine mammal. J Anim Ecol 2006; 75:408-20. [PMID: 16637994 DOI: 10.1111/j.1365-2656.2006.01057.x] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
1. We studied feeding frequency in free-ranging grey seals using stomach temperature telemetry to test if previously reported sex differences in the diving, movement and diet were reflected in the temporal pattern of foraging success. 2. Data were retrieved from 21 of 32 grey seals from 1999 to 2001, totalling 343 days and 555 feeding events, with individual record length varying from 2 to 40 days (mean: 16.33 +/- 2.67 days/seal). 3. Seals fed on 57.8 +/- 6.46% of days sampled and had an average of 1.7 +/- 0.26 meals per day, but individual variability was apparent in the temporal distribution of feeding as evidenced by high coefficients of variation (coefficient of variation = 69.0%). 4. Bout analysis of non-feeding intervals of six grey seals suggests that feeding intervals of individuals were varied and probably reflect differences in prey availability. Grey seals tended to have many single feeding events with long periods separating each event, as would be expected for a large carnivore with a batch-reactor digestive system. 5. We found significant sex differences in the temporal distribution of feeding. The number of feeding events per day was greater in males (2.2 +/- 0.4 vs. 1.0 +/- 0.2), as was time associated with feeding per day (56.6 +/- 5.8 min vs. 43.9 +/- 9.4 min). 6. The number of feeding events varied with time of day with the least number occurring during dawn. Feeding event size differed significantly by time of day, with greater meal sizes during the dawn and the smallest meals during the night. 7. The length of time between meals increased with the size of the previous meal, and was significantly less in males (541.4 +/- 63.5 min) than in females (1092.6 +/- 169.9 min). 8. These results provide new insight into the basis of sex differences in diving and diet in this large size-dimorphic marine predator.
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Affiliation(s)
- Deborah Austin
- Department of Biology, Dalhousie University, Halifax, Nova Scotia B2H 4J1, Canada.
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244
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Fowler MS, Ruokolainen L. Simple laboratory tests of ecological theories: What we can learn from them, and when we should be cautious. J Biosci 2006; 31:177-9. [PMID: 16809847 DOI: 10.1007/bf02703907] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Affiliation(s)
- Mike S Fowler
- Integrative Ecology Unit,Department of Biological and Environmental Science,PO Box 65, Viikinkaari 1,FI-00014,Helsinki University Finland.
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245
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Lin YK, Keane B, Isenhour A, Solomon NG. EFFECTS OF PATCH QUALITY ON DISPERSAL AND SOCIAL ORGANIZATION OF PRAIRIE VOLES: AN EXPERIMENTAL APPROACH. J Mammal 2006. [DOI: 10.1644/05-mamm-a-201r1.1] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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246
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Minderman J, Lind J, Cresswell W. Behaviourally mediated indirect effects: interference competition increases predation mortality in foraging redshanks. J Anim Ecol 2006; 75:713-23. [PMID: 16689954 DOI: 10.1111/j.1365-2656.2006.01092.x] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
1. The effect of competition for a limiting resource on the population dynamics of competitors is usually assumed to operate directly through starvation, yet may also affect survival indirectly through behaviourally mediated effects that affect risk of predation. Thus, competition can affect more than two trophic levels, and we aim here to provide an example of this. 2. We show that the foraging success of redshanks Tringa totanus (L.) foraging on active prey was highest in the front of flocks, whereas this was not the case for redshanks foraging on inactive prey. Also, when foraging on active prey, foraging success in a flock decreased as more birds passed through a patch, while overall foraging success was not lower on subsequent visits to the same patch. Thus, redshanks foraging on active prey suffered from interference competition, whereas this was not the case for redshanks foraging on inactive prey. 3. This interference competition led to differences in activity: redshanks attaining a lower foraging success had a higher walking rate. Greater activity was associated with wider flock spacing and shorter distances to cover, which has previously been shown to increase predation risk and mortality from sparrowhawks Accipiter nisus (L.). 4. We conclude that behavioural adaptations of prey species can lead to interference competition in foraging redshanks, and thus can affect their predation risk and mortality through increased activity. This study is one of the first to show how interference competition can be a mechanism for behaviourally mediated indirect effects, and provides further evidence for the suggestion that a single species occupying an intermediate trophic level may be simultaneously top-down controlled by a predator and bottom-up controlled by a behavioural response of its prey.
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Affiliation(s)
- Jeroen Minderman
- Centre for Ecological and Evolutionary Studies, Animal Ecology Group, University of Groningen, PO Box 14, 9750 AA Haren, The Netherlands.
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247
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Jolles AE, Etienne RS, Olff H. Independent and Competing Disease Risks: Implications for Host Populations in Variable Environments. Am Nat 2006; 167:745-57. [PMID: 16671018 DOI: 10.1086/503055] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2005] [Accepted: 01/12/2006] [Indexed: 11/03/2022]
Abstract
Disease models usually assume disease to act independently of other mortality- and morbidity-causing factors. Alternatively, disease may function as a competing risk factor, for example, killing already moribund hosts. Using tuberculosis (TB) in African buffalo as a model system, we explore consequences of competing or independent disease effects for host population dynamics. We include scenarios with density-dependent and density-independent effects of environmental variation, exemplified by variable food availability (driven by rainfall) and catastrophic droughts, respectively. Independent disease effects reduce population size linearly with prevalence, irrespective of the nature of environmental variation. Competing disease risks alter population size only if density-independent variation is present; then, disease reduces population size nonlinearly. Field data indicate that the net effect of TB on buffalo likely falls between the extremes of total independence and competition with other risk factors: TB increases mortality and decreases fecundity in some prime-aged buffalo, suggesting independent disease risks in these individuals, while similar disease effects in senescent buffalo may act as competing risks. Moreover, increased survival and fecundity of TB-negative buffalo may compensate for some disease-related losses. Model assumptions on independent or competing disease risks and environmental variability should be considered explicitly when assessing disease effects on wildlife populations.
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Affiliation(s)
- Anna E Jolles
- Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey 08544-1003, USA.
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248
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Wilmshurst J, Greer R, Henry J. Correlated cycles of snowshoe hares and Dall’s sheep lambs. CAN J ZOOL 2006. [DOI: 10.1139/z06-051] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We tested the hypothesis that the number of surviving lambs counted in mid-summer from a Dall’s sheep ( Ovis dalli Nelson, 1884) population on Sheep Mountain, Yukon, Canada, is correlated to the density of snowshoe hares ( Lepus americanus Erxleben, 1777) in the surrounding boreal forest. We examined correlations between the number of lambs and the number of snowshoe hares at different phases in the 10-year snowshoe hare cycle. There were significant cross-correlations between the ratio of lambs to nursery sheep and hare densities with 1- and 2-year time lags. Lamb numbers also showed clockwise rotation with respect to hare densities when points were joined chronologically. Simple population models suggest several relationships: when hare densities are high, lamb population growth rates are inversely related to hare densities; during the low phase of the hare population cycle, lamb population growth rates show density-independent fluctuations. In the absence of compelling evidence for direct interactions between Dall’s sheep and hares, we hypothesize that the inverse relationship between lamb population growth and hare density is mediated indirectly by shared predators.
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Affiliation(s)
- J.F. Wilmshurst
- Parks Canada, 145 McDermot Avenue, Winnipeg, MB R3B 0R1, Canada
- Kluane National Park and Reserve, P.O. Box 5495, Haines Junction, YT Y0B 1L0, Canada
| | - R. Greer
- Parks Canada, 145 McDermot Avenue, Winnipeg, MB R3B 0R1, Canada
- Kluane National Park and Reserve, P.O. Box 5495, Haines Junction, YT Y0B 1L0, Canada
| | - J.D. Henry
- Parks Canada, 145 McDermot Avenue, Winnipeg, MB R3B 0R1, Canada
- Kluane National Park and Reserve, P.O. Box 5495, Haines Junction, YT Y0B 1L0, Canada
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249
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Seivwright LJ, Redpath SM, Mougeot F, Leckie F, Hudson PJ. Interactions between intrinsic and extrinsic mechanisms in a cyclic species: testosterone increases parasite infection in red grouse. Proc Biol Sci 2006; 272:2299-304. [PMID: 16191643 PMCID: PMC1560195 DOI: 10.1098/rspb.2005.3233] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Field studies of mechanisms involved in population regulation have tended to focus on the roles of either intrinsic or extrinsic factors, but these are rarely mutually exclusive and their interactions can be crucial in determining dynamics. Experiments on red grouse Lagopus lagopus scoticus have shown that population instability can be caused both by the effects of a parasitic nematode, Trichostrongylus tenuis, on host production or by changes in testosterone influencing aggressive behaviour and recruitment. We experimentally tested for an interaction between testosterone and T. tenuis in free-living male grouse. A total of 123 grouse were caught in autumn, treated with an anthelmintic to remove parasites, and then given either testosterone or empty, control, implants. After one month grouse were re-infected with a standard dose of parasites. We show that males with increased testosterone levels had greater parasite intensities than controls after one year. We discuss possible physiological and behavioural mechanisms linking testosterone and increased parasite intensity, and the implications for our understanding of complex, unstable population dynamics.
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Affiliation(s)
- Linzi J Seivwright
- Centre for Ecology and Hydrology Hill of BrathensBanchory, Aberdeenshire AB31 4BW, UK
| | - Stephen M Redpath
- Centre for Ecology and Hydrology Hill of BrathensBanchory, Aberdeenshire AB31 4BW, UK
- IREC (CSIC-UCLM-JCCM) Ronda de Toledo13005 Ciudad Real, Spain
- Author for correspondence ()
| | - François Mougeot
- Centre for Ecology and Hydrology Hill of BrathensBanchory, Aberdeenshire AB31 4BW, UK
| | - Fiona Leckie
- Centre for Ecology and Hydrology Hill of BrathensBanchory, Aberdeenshire AB31 4BW, UK
| | - Peter J Hudson
- Center for Infectious Disease Dynamics, Biology Department, Mueller Lab Penn State UniversityUniversity Park, PA 16802, USA
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Owen-Smith N, Mills MGL. MANIFOLD INTERACTIVE INFLUENCES ON THE POPULATION DYNAMICS OF A MULTISPECIES UNGULATE ASSEMBLAGE. ECOL MONOGR 2006. [DOI: 10.1890/04-1101] [Citation(s) in RCA: 96] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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