1
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Forsythe AB, Day T, Nelson WA. Demystifying individual heterogeneity. Ecol Lett 2021; 24:2282-2297. [PMID: 34288328 DOI: 10.1111/ele.13843] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2021] [Revised: 06/07/2021] [Accepted: 06/14/2021] [Indexed: 12/01/2022]
Abstract
Among-individual variation in vital rates, such as mortality and birth rates, exists in nearly all populations. Recent studies suggest that this individual heterogeneity produces substantial life-history and fitness differences among individuals, which in turn scale up to influence population dynamics. However, our ability to understand the consequences of individual heterogeneity is limited by inconsistencies across conceptual frameworks in the field. Studies of individual heterogeneity remain filled with contradicting and ambiguous terminology that introduces risks of misunderstandings, conflicting models and unreliable conclusions. Here, we synthesise the existing literature into a single and comparatively straightforward framework with explicit terminology and definitions. This work introduces a distinction between potential vital rates and realised vital rates to develop a coherent framework that maps directly onto mathematical models of individual heterogeneity. We suggest the terms "fixed condition" and "dynamic condition" be used to distinguish potential vital rates that are permanent from those that can change throughout an individual's life. To illustrate, we connect the framework to quantitative genetics models and to common classes of statistical models used to infer individual heterogeneity. We also develop a population projection matrix model that provides an example of how our definitions are translated into precise quantitative terms.
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Affiliation(s)
- Amy B Forsythe
- Department of Biology, Biosciences Complex, Queen's University, Kingston, ON, Canada
| | - Troy Day
- Department of Biology, Biosciences Complex, Queen's University, Kingston, ON, Canada.,Department of Mathematics and Statistics, Queen's University, Kingston, ON, Canada
| | - William A Nelson
- Department of Biology, Biosciences Complex, Queen's University, Kingston, ON, Canada
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2
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Ma ZS. A unified survival-analysis approach to insect population development and survival times. Sci Rep 2021; 11:8223. [PMID: 33859237 PMCID: PMC8050314 DOI: 10.1038/s41598-021-87264-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2020] [Accepted: 03/24/2021] [Indexed: 11/29/2022] Open
Abstract
There are two major categories of observation data in studying time-dependent processes: one is the time-series data, and the other is the perhaps lesser-recognized but similarly prevalent time-to-event data (also known as survival or failure time). Examples in entomology include molting times and death times of insects, waiting times of predators before the next attack or the hiding times of preys. A particular challenge in analyzing time-to-event data is the observation censoring, or the incomplete observation of survival times, dealing which is a unique advantage of survival analysis statistics. Even with a perfectly designed experiment being conducted perfectly, such ‘naturally’ censoring may still be unavoidable due to the natural processes, including the premature death in the observation of insect development, the variability in instarship, or simply the continuous nature of time process and the discrete nature of sampling intervals. Here we propose to apply the classic Cox proportional hazards model for modeling both insect development and survival rates (probabilities) with a unified survival analysis approach. We demonstrated the advantages of the proposed approach with the development and survival datasets of 1800 Russian wheat aphids from their births to deaths, observed under 25 laboratory treatments of temperatures and plant growth stages.
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Affiliation(s)
- Zhanshan Sam Ma
- Computational Biology and Medical Ecology Lab, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming, China. .,Center for Excellence in Animal Evolution and Genetics, Chinese Academy of Sciences, Kunming, China. .,Department of Entomology, Plant Pathology and Nematology, University of Idaho, Moscow, ID, 83843, USA.
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3
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Guindre-Parker S, Rubenstein DR. Survival Benefits of Group Living in a Fluctuating Environment. Am Nat 2020; 195:1027-1036. [PMID: 32469654 DOI: 10.1086/708496] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
Group living is predicted to arise only when the fitness benefits outweigh the costs of sociality. Group-living species-including cooperatively breeding and family-living birds and mammals-occur most frequently in environments where climatic conditions fluctuate unpredictably from year to year. The fitness consequences of group living are thus expected to vary with changing environmental conditions, though few studies have examined this possibility. We examined whether living in large social groups improves adult survivorship in cooperatively breeding superb starlings (Lamprotornis superbus). We also tested the hypothesis that larger groups buffer against harsh conditions by increasing survivorship most under periods of low rainfall. We found that group size was positively correlated with adult survival but in a sex-specific manner: female survival increased with group size across all environmental conditions, whereas male survival increased with group size only in wet years. Together with previous work in this system, our results suggest that larger groups confer survival benefits by reducing predation, rather than by improving access to food or buffering against physiological stress. Although group living does not appear to buffer against harsh conditions in adult starlings living in a fluctuating environment, living in larger groups does confer a survival advantage.
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4
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Colchero F, Kiyakoglu BY. Beyond the proportional frailty model: Bayesian estimation of individual heterogeneity on mortality parameters. Biom J 2019; 62:124-135. [PMID: 31574180 DOI: 10.1002/bimj.201800280] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2018] [Revised: 07/08/2019] [Accepted: 07/29/2019] [Indexed: 11/09/2022]
Abstract
Today, we know that demographic rates can be greatly influenced by differences among individuals in their capacity to survive and reproduce. These intrinsic differences, commonly known as individual heterogeneity, can rarely be measured and are thus treated as latent variables when modeling mortality. Finite mixture models and mixed effects models have been proposed as alternative approaches for inference on individual heterogeneity in mortality. However, in general models assume that individual heterogeneity influences mortality proportionally, which limits the possibility to test hypotheses on the effect of individual heterogeneity on other aspects of mortality such as ageing rates. Here, we propose a Bayesian model that builds upon the mixture models previously developed, but that facilitates making inferences on the effect of individual heterogeneity on mortality parameters other than the baseline mortality. As an illustration, we apply this framework to the Gompertz-Makeham mortality model, commonly used in human and wildlife studies, by assuming that the Gompertz rate parameter is affected by individual heterogeneity. We provide results of a simulation study where we show that the model appropriately retrieves the parameters used for simulation, even for low variances in the heterogeneous parameter. We then apply the model to a dataset on captive chimpanzees and on a cohort life table of 1751 Swedish men, and show how model selection against a null model (i.e., without heterogeneity) can be carried out.
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Affiliation(s)
- Fernando Colchero
- Department of Mathematics and Computer Science, University of Southern Denmark, Odense, Denmark.,Interdisciplinary Center on Population Dynamics, University of Southern Denmark, Odense, Denmark
| | - Burhan Y Kiyakoglu
- Department of Mathematics and Computer Science, University of Southern Denmark, Odense, Denmark
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5
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Ng'weno CC, Buskirk SW, Georgiadis NJ, Gituku BC, Kibungei AK, Porensky LM, Rubenstein DI, Goheen JR. Apparent Competition, Lion Predation, and Managed Livestock Grazing: Can Conservation Value Be Enhanced? Front Ecol Evol 2019. [DOI: 10.3389/fevo.2019.00123] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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6
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Lescroël A, Ballard G, Massaro M, Dugger K, Jennings S, Pollard A, Porzig E, Schmidt A, Varsani A, Grémillet D, Ainley D. Evidence of age-related improvement in the foraging efficiency of Adélie penguins. Sci Rep 2019; 9:3375. [PMID: 30833598 PMCID: PMC6399253 DOI: 10.1038/s41598-019-39814-x] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2018] [Accepted: 01/30/2019] [Indexed: 11/21/2022] Open
Abstract
Age variation in reproductive performance is well-documented but the mechanisms underlying this variation remain unclear. Foraging efficiency is likely to be a key source of demographic variation as it determines the amount of energy that can be invested in fitness-related activities. Evidence of age-related changes in the foraging efficiency of adult seabirds is scarce and inconsistent. We investigated the effects of age on the foraging efficiency of breeding Adélie penguins, a relatively short-lived seabird species, in order to gain a broader perspective on the processes driving variation in ageing rates. We found support for a positive effect of age, either linear or levelling off at old ages, on both our proxies for daily catch rate and catch per unit effort. Across all age classes, males were more performant foragers than females. We found no strong evidence for differing ageing patterns between sexes or individual quality levels, and no evidence for senescence. We infer that continuous individual improvement could be responsible for a larger amount of the variation in foraging efficiency with age at our study site, compared with selective disappearance of underperforming phenotypes. The different results reported by other studies highlight the need to conduct longitudinal studies across a range of species in different environments.
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Affiliation(s)
- Amélie Lescroël
- Point Blue Conservation Science, Petaluma, CA, 94954, USA. .,Centre d'Ecologie Fonctionnelle et Evolutive, UMR 5175, CNRS - Université de Montpellier - Université Paul-Valéry Montpellier - EPHE, Montpellier, France.
| | - Grant Ballard
- Point Blue Conservation Science, Petaluma, CA, 94954, USA
| | - Melanie Massaro
- School of Environmental Sciences, Institute for Land, Water and Society, Charles Sturt University, Albury, NSW, 2640, Australia
| | - Katie Dugger
- U.S. Geological Survey, Oregon Cooperative Fish and Wildlife Research Unit, Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon, USA
| | - Scott Jennings
- Point Blue Conservation Science, Petaluma, CA, 94954, USA.,U.S. Geological Survey, Oregon Cooperative Fish and Wildlife Research Unit, Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon, USA
| | - Annie Pollard
- Point Blue Conservation Science, Petaluma, CA, 94954, USA
| | | | - Annie Schmidt
- Point Blue Conservation Science, Petaluma, CA, 94954, USA
| | - Arvind Varsani
- The Biodesign Center for Fundamental and Applied Microbiomics, Center for Evolution and Medicine, School of Life sciences, Arizona State University, Tempe, Arizona, USA.,Structural Biology Research Unit, Department of Clinical Laboratory Sciences, University of Cape Town, Observatory, Cape Town, South Africa
| | - David Grémillet
- Centre d'Ecologie Fonctionnelle et Evolutive, UMR 5175, CNRS - Université de Montpellier - Université Paul-Valéry Montpellier - EPHE, Montpellier, France.,FitzPatrick Institute, DST/NRF centre of excellence at the University of Cape Town, Rondebosch, 7701, South Africa
| | - David Ainley
- H.T. Harvey & Associates, Los Gatos, California, USA
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7
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McFarlane S, Manseau M, Flasko A, Horn RL, Arnason N, Neufeld L, Bradley M, Wilson P. Genetic influences on male and female variance in reproductive success and implications for the recovery of severely endangered mountain caribou. Glob Ecol Conserv 2018. [DOI: 10.1016/j.gecco.2018.e00451] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
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8
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Louthan A, Doak D. Measurement error of state variables creates substantial bias in results of demographic population models. Ecology 2018; 99:2308-2317. [PMID: 30007078 DOI: 10.1002/ecy.2455] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/26/2017] [Revised: 06/05/2018] [Accepted: 06/24/2018] [Indexed: 11/06/2022]
Abstract
Integral projection and matrix population models are commonly used in ecological and conservation studies to assess the health and extinction risk of populations. These models use one (or more) measurable state variable(s), such as size or age, to predict individual performance, which, ideally, is the sole determinant of an individual's expected fate. However, even if ecologists successfully identify and measure the observable state variable(s) that best predicts individual fate, we are rarely, if ever, able to perfectly measure state for many species, especially those with size structure, where total plant biomass or starch stores, for example, may be the best predictors of fate. Here, we used a series of simulations to test how this imperfect quantification of actual state ("measurement error") leads to inaccurate prediction of state-dependent fates and influences the predictions of structured population models. We simulated 10 yr of best practice field data collection using known vital rate functions and incorporated measurement error of different magnitudes and types (completely random, temporal, and individual based) for two size-structured life histories. We found that even for conservative error rates, most types of measurement error increased the median predicted population growth rate by 1-2% growth per year. However, the magnitude of this error differed substantially with life history strategy and error type, with some scenarios resulting in >8% median overestimation of population growth rate. This effect arises largely from the well-known econometrics problem of "regression dilution" (overestimation of the intercept and underestimation of the slope of a regression when the predictor variable is measured with error), which in our simulations typically results in overly optimistic predictions of small or young individuals' vital rates. Our results suggest that the problem of measurement error for state variables, present in many demographic studies but virtually unacknowledged in the ecological literature, may lead to substantial misestimation of population behavior, resulting in erroneous inferences about not only growth, but also extinction risk and other aspects of population dynamics.
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Affiliation(s)
- Allison Louthan
- Department of Biology, Duke University, Durham, North Carolina, 27708, USA.,Environmental Studies Program, University of Colorado-Boulder, Boulder, Colorado, 80301, USA
| | - Daniel Doak
- Environmental Studies Program, University of Colorado-Boulder, Boulder, Colorado, 80301, USA
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9
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Snyder RE, Ellner SP. Pluck or Luck: Does Trait Variation or Chance Drive Variation in Lifetime Reproductive Success? Am Nat 2018; 191:E90-E107. [DOI: 10.1086/696125] [Citation(s) in RCA: 45] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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10
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Jenouvrier S, Aubry LM, Barbraud C, Weimerskirch H, Caswell H, Childs D. Interacting effects of unobserved heterogeneity and individual stochasticity in the life history of the southern fulmar. J Anim Ecol 2018; 87:212-222. [PMID: 28886208 PMCID: PMC5765524 DOI: 10.1111/1365-2656.12752] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2017] [Accepted: 08/03/2017] [Indexed: 11/29/2022]
Abstract
Individuals are heterogeneous in many ways. Some of these differences are incorporated as individual states (e.g. age, size, breeding status) in population models. However, substantial amounts of heterogeneity may remain unaccounted for, due to unmeasurable genetic, maternal or environmental factors. Such unobserved heterogeneity (UH) affects the behaviour of heterogeneous cohorts via intra-cohort selection and contributes to inter-individual variance in demographic outcomes such as longevity and lifetime reproduction. Variance is also produced by individual stochasticity, due to random events in the life cycle of wild organisms, yet no study thus far has attempted to decompose the variance in demographic outcomes into contributions from UH and individual stochasticity for an animal population in the wild. We developed a stage-classified matrix population model for the southern fulmar breeding on Ile des Pétrels, Antarctica. We applied multievent, multistate mark-recapture methods to estimate a finite mixture model accounting for UH in all vital rates and Markov chain methods to calculate demographic outcomes. Finally, we partitioned the variance in demographic outcomes into contributions from UH and individual stochasticity. We identify three UH groups, differing substantially in longevity, lifetime reproductive output, age at first reproduction and in the proportion of the life spent in each reproductive state. -14% of individuals at fledging have a delayed but high probability of recruitment and extended reproductive life span. -67% of individuals are less likely to reach adulthood, recruit late and skip breeding often but have the highest adult survival rate. -19% of individuals recruit early and attempt to breed often. They are likely to raise their offspring successfully, but experience a relatively short life span. Unobserved heterogeneity only explains a small fraction of the variances in longevity (5.9%), age at first reproduction (3.7%) and lifetime reproduction (22%). UH can affect the entire life cycle, including survival, development and reproductive rates, with consequences over the lifetime of individuals and impacts on cohort dynamics. The respective role of UH vs. individual stochasticity varies greatly among demographic outcomes. We discuss the implication of our finding for the gradient of life-history strategies observed among species and argue that individual differences should be accounted for in demographic studies of wild populations.
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Affiliation(s)
- Stéphanie Jenouvrier
- Biology DepartmentWoods Hole Oceanographic InstitutionWoods HoleMAUSA
- Centre d’Etudes Biologiques de Chizé, UMR 7372 CNRSUniv La RochelleVilliers en BoisFrance
| | - Lise M. Aubry
- Fish, Wildlife and Conservation Biology DepartmentColorado State UniversityFort CollinsCOUSA
| | - Christophe Barbraud
- Centre d’Etudes Biologiques de Chizé, UMR 7372 CNRSUniv La RochelleVilliers en BoisFrance
| | - Henri Weimerskirch
- Centre d’Etudes Biologiques de Chizé, UMR 7372 CNRSUniv La RochelleVilliers en BoisFrance
| | - Hal Caswell
- Biology DepartmentWoods Hole Oceanographic InstitutionWoods HoleMAUSA
- Institute for Biodiversity and Ecosystem Dynamics, University of AmsterdamAmsterdamThe Netherlands
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11
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Kendall BE, Fox GA, Stover JP. Boldness-aggression syndromes can reduce population density: behavior and demographic heterogeneity. Behav Ecol 2017. [DOI: 10.1093/beheco/arx068] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Affiliation(s)
- Bruce E Kendall
- Bren School of Environmental Science & Management, University of California Santa Barbara, Santa Barbara, CA, USA
| | - Gordon A Fox
- Department of Integrative Biology, University of South Florida, Tampa, FL, USA
| | - Joseph P Stover
- Department of Mathematics, Lyon College, Batesville, AR, USA
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12
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Cressler CE, Bengtson S, Nelson WA. Unexpected Nongenetic Individual Heterogeneity and Trait Covariance in Daphnia and Its Consequences for Ecological and Evolutionary Dynamics. Am Nat 2017; 190:E13-E27. [DOI: 10.1086/691779] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
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13
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Puy A, Muneepeerakul R, Balbo AL. Size and stochasticity in irrigated social-ecological systems. Sci Rep 2017; 7:43943. [PMID: 28266656 PMCID: PMC5339736 DOI: 10.1038/srep43943] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2016] [Accepted: 01/31/2017] [Indexed: 11/16/2022] Open
Abstract
This paper presents a systematic study of the relation between the size of irrigation systems and the management of uncertainty. We specifically focus on studying, through a stylized theoretical model, how stochasticity in water availability and taxation interacts with the stochastic behavior of the population within irrigation systems. Our results indicate the existence of two key population thresholds for the sustainability of any irrigation system: or the critical population size required to keep the irrigation system operative, and N* or the population threshold at which the incentive to work inside the irrigation system equals the incentives to work elsewhere. Crossing irretrievably leads to system collapse. N* is the population level with a sub-optimal per capita payoff towards which irrigation systems tend to gravitate. When subjected to strong stochasticity in water availability or taxation, irrigation systems might suffer sharp population drops and irreversibly disintegrate into a system collapse, via a mechanism we dub 'collapse trap'. Our conceptual study establishes the basis for further work aiming at appraising the dynamics between size and stochasticity in irrigation systems, whose understanding is key for devising mitigation and adaptation measures to ensure their sustainability in the face of increasing and inevitable uncertainty.
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Affiliation(s)
- Arnald Puy
- Department of Maritime Civilizations, Recanati Institute for Maritime Studies, University of Haifa, 199 Aba Koushy Ave, Mount Carmel, 3498838 Haifa, Israel
- Geographisches Institut, Universität zu Köln, Zülphicher Strasse 45, 50674 Cologne, Germany
| | - Rachata Muneepeerakul
- Department of Agricultural and Biological Engineering, University of Florida, Gainesville, Florida, PO Box 110570, USA
| | - Andrea L. Balbo
- Research Group Climate Change and Security (CLISEC), KlimaCampus, Center for Earth System Research and Sustainability (CEN), University of Hamburg, Grindelberg 5/7, 20144 Hamburg, Germany
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14
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Cam E, Aubry LM, Authier M. The Conundrum of Heterogeneities in Life History Studies. Trends Ecol Evol 2016; 31:872-886. [DOI: 10.1016/j.tree.2016.08.002] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2016] [Revised: 08/17/2016] [Accepted: 08/18/2016] [Indexed: 12/21/2022]
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15
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16
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Consequences of dispersal heterogeneity for population spread and persistence. Bull Math Biol 2014; 76:2681-710. [PMID: 25348060 DOI: 10.1007/s11538-014-0014-z] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2013] [Accepted: 08/18/2014] [Indexed: 10/24/2022]
Abstract
Dispersal heterogeneity is increasingly being observed in ecological populations and has long been suspected as an explanation for observations of non-Gaussian dispersal. Recent empirical and theoretical studies have begun to confirm this. Using an integro-difference model, we allow an individual's diffusivity to be drawn from a trait distribution and derive a general relationship between the dispersal kernel's moments and those of the underlying heterogeneous trait distribution. We show that dispersal heterogeneity causes dispersal kernels to appear leptokurtic, increases the population's spread rate, and lowers the critical reproductive rate required for persistence in the face of advection. Wavespeed has been shown previously to be determined largely by the form of the dispersal kernel tail. We qualify this by showing that when reproduction is low, the precise shape of the tail is less important than the first few dispersal moments such as variance and kurtosis. If the reproductive rate is large, a dispersal kernel's asymptotic tail has a greater influence over wavespeed, implying that estimating the prevalence of traits which correlate with long-range dispersal is critical. The presence of multiple dispersal behaviors has previously been characterized in terms of long-range versus short-range dispersal, and it has been found that rare long-range dispersal essentially determines wavespeed. We discuss this finding and place it within a general context of dispersal heterogeneity showing that the dispersal behavior with the highest average dispersal distance does not always determine wavespeed.
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17
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Chambert T, Rotella JJ, Higgs MD, Garrott RA. Individual heterogeneity in reproductive rates and cost of reproduction in a long-lived vertebrate. Ecol Evol 2013; 3:2047-60. [PMID: 23919151 PMCID: PMC3728946 DOI: 10.1002/ece3.615] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2013] [Revised: 04/18/2013] [Accepted: 04/24/2013] [Indexed: 01/28/2023] Open
Abstract
Individual variation in reproductive success is a key feature of evolution, but also has important implications for predicting population responses to variable environments. Although such individual variation in reproductive outcomes has been reported in numerous studies, most analyses to date have not considered whether these realized differences were due to latent individual heterogeneity in reproduction or merely random chance causing different outcomes among like individuals. Furthermore, latent heterogeneity in fitness components might be expressed differently in contrasted environmental conditions, an issue that has only rarely been investigated. Here, we assessed (i) the potential existence of latent individual heterogeneity and (ii) the nature of its expression (fixed vs. variable) in a population of female Weddell seals (Leptonychotes weddellii), using a hierarchical modeling approach on a 30-year mark–recapture data set consisting of 954 individual encounter histories. We found strong support for the existence of latent individual heterogeneity in the population, with “robust” individuals expected to produce twice as many pups as “frail” individuals. Moreover, the expression of individual heterogeneity appeared consistent, with only mild evidence that it might be amplified when environmental conditions are severe. Finally, the explicit modeling of individual heterogeneity allowed us to detect a substantial cost of reproduction that was not evidenced when the heterogeneity was ignored.
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Affiliation(s)
- Thierry Chambert
- Department of Ecology, Montana State University Bozeman, Montana, 59717
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18
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Barbraud C, Tuck GN, Thomson R, Delord K, Weimerskirch H. Fisheries bycatch as an inadvertent human-induced evolutionary mechanism. PLoS One 2013; 8:e60353. [PMID: 23593199 PMCID: PMC3622665 DOI: 10.1371/journal.pone.0060353] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2012] [Accepted: 02/26/2013] [Indexed: 11/18/2022] Open
Abstract
Selective harvesting of animals by humans can affect the sustainability and genetics of their wild populations. Bycatch - the accidental catch of non-target species - spans the spectrum of marine fauna and constitutes a harvesting pressure. Individual differences in attraction to fishing vessels and consequent susceptibility to bycatch exist, but few studies integrate this individual heterogeneity with demography. Here, we tested for the evidence and consequences of individual heterogeneity on the demography of the wandering albatross, a seabird heavily affected by fisheries bycatch. We found strong evidence for heterogeneity in survival with one group of individuals having a 5.2% lower annual survival probability than another group, and a decrease in the proportion of those individuals with the lowest survival in the population coinciding with a 7.5 fold increase in fishing effort in the foraging areas. Potential causes for the heterogeneity in survival are discussed and we suggest that bycatch removed a large proportion of individuals attracted by fishing vessels and had significant phenotypic and population consequences.
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19
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Saino N, Romano M, Ambrosini R, Rubolini D, Boncoraglio G, Caprioli M, Romano A. Longevity and lifetime reproductive success of barn swallow offspring are predicted by their hatching date and phenotypic quality. J Anim Ecol 2012; 81:1004-12. [PMID: 22531043 DOI: 10.1111/j.1365-2656.2012.01989.x] [Citation(s) in RCA: 77] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
1. Longevity is a major determinant of individual differences in Darwinian fitness. Several studies have analyzed the stochastic, time-dependent causes of variation in longevity, but little information exists from free-ranging animal populations on the effects that environmental conditions and phenotype early in ontogeny have on duration of life. 2. In this long-term (1993-2011) study of a migratory, colonial, passerine bird, the barn swallow (Hirundo rustica), we analyzed longevity and, in a subsample of individuals, lifetime reproductive success (LRS) of the offspring that reached sexual maturity in relation to hatching date, which can affect the rearing environment through a seasonal deterioration in ecological conditions. Moreover, we analyzed the consequences of variation in body size and, for the first time in any species, of a major component of immunity on longevity, both by looking at absolute phenotypic values and at deviations from the brood mean. 3. Accelerated failure time models showed that individuals of both sexes that hatched early in any breeding season enjoyed larger longevity and larger LRS, indicating directional selection for early breeding. Both male and female offspring with large T cell-mediated immune response relative to their siblings and female nestlings that dominated the brood size/age hierarchy had larger longevity than their siblings of inferior phenotypic quality/age. Conversely, absolute phenotypic values did not predict longevity. 4. Frailty modelling disclosed marked spatial heterogeneity in longevity among colonies of origin, again stressing the impact of rearing conditions on longevity. 5. This study therefore reinforces the notion that perinatal environment and maternal decisions over timing and site of breeding, and position in the brood hierarchy can have marked effects on progeny life history that extend well into adulthood. In addition, it provides the first evidence from any bird population in the wild that immune response when nestlings predicts individuals' longevity after sexual maturation.
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Affiliation(s)
- Nicola Saino
- Dipartimento di Biologia, Università di Milano, via Celoria 26, I-20133 Milano, Italy.
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20
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Kendall BE, Fox GA, Fujiwara M, Nogeire TM. Demographic heterogeneity, cohort selection, and population growth. Ecology 2011; 92:1985-93. [PMID: 22073789 DOI: 10.1890/11-0079.1] [Citation(s) in RCA: 67] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Demographic heterogeneity--variation among individuals in survival and reproduction--is ubiquitous in natural populations. Structured population models address heterogeneity due to age, size, or major developmental stages. However, other important sources of demographic heterogeneity, such as genetic variation, spatial heterogeneity in the environment, maternal effects, and differential exposure to stressors, are often not easily measured and hence are modeled as stochasticity. Recent research has elucidated the role of demographic heterogeneity in changing the magnitude of demographic stochasticity in small populations. Here we demonstrate a previously unrecognized effect: heterogeneous survival in long-lived species can increase the long-term growth rate in populations of any size. We illustrate this result using simple models in which each individual's annual survival rate is independent of age but survival may differ among individuals within a cohort. Similar models, but with nonoverlapping generations, have been extensively studied by demographers, who showed that, because the more "frail" individuals are more likely to die at a young age, the average survival rate of the cohort increases with age. Within ecology and evolution, this phenomenon of "cohort selection" is increasingly appreciated as a confounding factor in studies of senescence. We show that, when placed in a population model with overlapping generations, this heterogeneity also causes the asymptotic population growth rate lambda to increase, relative to a homogeneous population with the same mean survival rate at birth. The increase occurs because, even integrating over all the cohorts in the population, the population becomes increasingly dominated by the more robust individuals. The growth rate increases monotonically with the variance in survival rates, and the effect can be substantial, easily doubling the growth rate of slow-growing populations. Correlations between parent and offspring phenotype change the magnitude of the increase in lambda, but the increase occurs even for negative parent-offspring correlations. The effect of heterogeneity in reproductive rate on lambda is quite different: growth rate increases with reproductive heterogeneity for positive parent-offspring correlation but decreases for negative parent-offspring correlation. These effects of demographic heterogeneity on lambda have important implications for population dynamics, population viability analysis, and evolution.
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Affiliation(s)
- Bruce E Kendall
- Bren School of Environmental Science and Management, University of California, Santa Barbara, California 93101-5131, USA.
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21
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Che-Castaldo JP, Inouye DW. The effects of dataset length and mast seeding on the demography ofFrasera speciosa, a long-lived monocarpic plant. Ecosphere 2011. [DOI: 10.1890/es11-00263.1] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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22
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Marzolin G, Charmantier A, Gimenez O. Frailty in state-space models: application to actuarial senescence in the Dipper. Ecology 2011; 92:562-7. [PMID: 21608464 DOI: 10.1890/10-0306.1] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Senescence, a decrease in life history traits with age, is a within-individual process. The lack of suitable methods to deal with individual heterogeneity has long impeded progress in exploring senescence in wild populations. Analyses of survival senescence are additionally complicated by the often neglected issue of imperfect detectability. To deal with both these issues, we developed state-space models to analyze capture-mark-recapture data while accounting for individual heterogeneity by incorporating random effects. We illustrated our approach by applying it to 29 years of data on breeding females in a Dipper (Cinclus cinclus) population. We highlighted patterns of age-related variation in annual survival by statistical comparisons of piecewise linear, quadratic, Gompertz, and Weibull survival models. The Gompertz model was ranked first in our set. It provided strong evidence for actuarial senescence with an onset of senescence estimated at about 2.3 years. The probability for this model to involve a frailty was 0.15, and the probability to involve an individual latent effect in detection was about 0.4. The estimated mean age at first reproduction was 1.2 years. The general case model described here in detail should encourage the reanalysis of actuarial senescence in cases where imperfect detection or individual heterogeneity is suspected.
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Affiliation(s)
- Gilbert Marzolin
- Centre d'Ecologie Evolutive et Fonctionnelle UMR 5175, Campus CNRS, 1919 Route de Mende 34293, Montpellier Cedex 5 France.
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Dugaw CJ, Ram K. Individual heterogeneity in mortality mediates long-term persistence of a seasonal microparasite. Oecologia 2011; 166:317-25. [PMID: 21113626 PMCID: PMC3094528 DOI: 10.1007/s00442-010-1844-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2010] [Accepted: 11/03/2010] [Indexed: 11/28/2022]
Abstract
One of the primary objectives in population ecology is to understand mechanisms that allow a species to persist or to be driven to extinction. In most population models, individuals are assumed to be equivalent within any particular category such as age, sex, or morphological grouping. Individuals within such groupings, however, may exhibit considerable variation in traits that can significantly affect population trajectories. Although ecologists have long been aware of such variation, they are frequently ignored to maintain computational tractability. The few statistical models that do incorporate such heterogeneity require prohibitively large amounts of data on many individuals, making them impractical. In California's coastal prairie, a parasitic nematode, Heterorhabditis marelatus, is an important natural enemy, whose presence determines the strength and extent of a trophic cascade. Mortality of H. marelatus is strongly influenced by habitat and seasonality, which determines long-term persistence. Prior efforts to estimate mortality have suffered from difficulty in distinguishing between measurement and process error due to limitations in experimental protocol. In this study, we eliminate measurement error in the initial population size and focus on the true nature of the heterogeneity in mortality. By including individual heterogeneity in our statistical model, we are able to understand how this species is able to persist over seasonally harsh environmental conditions. Further, we extrapolate these findings to larger population sizes and illustrate that heterogeneous survival can have a significant effect on the emergent number of survivors.
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Affiliation(s)
- Christopher J Dugaw
- Department of Mathematics, Humboldt State University, Arcata, CA 95521, USA.
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Aubry LM, Cam E, Koons DN, Monnat JY, Pavard S. Drivers of age-specific survival in a long-lived seabird: contributions of observed and hidden sources of heterogeneity. J Anim Ecol 2010; 80:375-83. [DOI: 10.1111/j.1365-2656.2010.01784.x] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Ma ZS. Survival analysis approach to insect life table analysis and hypothesis testing: with particular reference to Russian wheat aphid (Diuraphis noxia (Mordvilko)) populations. BULLETIN OF ENTOMOLOGICAL RESEARCH 2010; 100:315-324. [PMID: 19941673 DOI: 10.1017/s0007485309990356] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
The goal of this paper is to examine and demonstrate that survival analysis, which has been a de facto standard in biomedical research since the 1990s but has not been widely adopted in entomology yet, should possess similar potential in entomological research. The following three objectives are set to achieve this goal: (i) addressing a fundamental issue - censoring or incomplete observations; (ii) demonstrating the application of survival analysis to analyze insect life tables; and (iii) applying survival analysis for hypothesis testing. The data used to demonstrate the applications is from our laboratory experiments, which recorded the development, survival and reproduction of 1800 Russian wheat aphids (Diuraphis noxia (Mordvilko), RWA) under 25 treatments of temperature and plant-growth stage. With regard to the first two objectives, besides examining the near ubiquitous existence of censoring in insect population research, we constructed and analyzed life tables of 1800 RWA individuals with survival analysis. We further demonstrate that there could be very significant differences in life table parameters, such as median development times with and without considering censoring. To the best of our knowledge, this is the first recognition in entomology that censoring, which is hardly avoidable, can cause significant systematical bias (ranging between 4-25%; table 1) in insect development data analysis. As for the third objective, the study shows that four statistics from survival analysis can be applied to testing the effects of covariates, such as temperature and plant-growth stage, on development and survival of the Russian wheat aphid. The advantages of survival analysis include the handling of censored observations, survival probabilities in the form of rigorous survivor function vs. simple survival rates, dynamic modeling of covariates effects on development and survival with a unified model structure, etc. The methods demonstrated in this article should also be useful for entomological research beyond insect demography, such as bioassay, assessment of natural enemies, the studies of insect behaviors, etc.
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Affiliation(s)
- Z S Ma
- Department of Entomology, University of Idaho, Moscow, ID 83844, USA.
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Abstract
Demographic stochasticity can have large effects on the dynamics of small populations as well as on the persistence of rare genotypes and lineages. Survival is sensibly modeled as a binomial process, but annual reproductive success (ARS) is more complex and general models for demographic stochasticity do not exist. Here we introduce a stochastic model framework for ARS and illustrate some of its properties. We model a sequence of stochastic events: nest completion, the number of eggs or neonates produced, nest predation, and the survival of individual offspring to independence. We also allow multiple nesting attempts within a breeding season. Most of these components can be described by Bernoulli or binomial processes; the exception is the distribution of offspring number. Using clutch and litter size distributions from 53 vertebrate species, we demonstrate that among-individual variability in offspring number can usually be described by the generalized Poisson distribution. Our model framework allows the demographic variance to be calculated from underlying biological processes and can easily be linked to models of environmental stochasticity or selection because of its parametric structure. In addition, it reveals that the distributions of ARS are often multimodal and skewed, with implications for extinction risk and evolution in small populations.
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Affiliation(s)
- Bruce E Kendall
- Donald Bren School of Environmental Science and Management, University of California, Santa Barbara, CA 93106, USA.
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Péron G, Crochet PA, Choquet R, Pradel R, Lebreton JD, Gimenez O. Capture-recapture models with heterogeneity to study survival senescence in the wild. OIKOS 2010. [DOI: 10.1111/j.1600-1706.2009.17882.x] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Reid JM, Bignal EM, Bignal S, McCracken DI, Bogdanova MI, Monaghan P. Parent age, lifespan and offspring survival: structured variation in life history in a wild population. J Anim Ecol 2010; 79:851-62. [PMID: 20202008 DOI: 10.1111/j.1365-2656.2010.01669.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
1. Understanding the degree to which reproductive success varies with an individual's age and lifespan, and the degree to which population-level variation mirrors individual-level variation, is central to understanding life-history evolution and the dynamics of age-structured populations. We quantified variation in the survival probability of offspring, one key component of reproductive success and fitness, in relation to parent age and lifespan in a wild population of red-billed choughs (Pyrrhocorax pyrrhocorax). 2. On average across the study population, the first-year survival probability of offspring decreased with increasing parent age and lifespan; offspring of old parents were less likely to survive than offspring of young parents, and offspring of long-lived parents were less likely to survive than offspring of short-lived parents. 3. However, survival did not vary with parent age across offspring produced by groups of parents that ultimately had similar lifespans. 4. Rather, across offspring produced by young parents, offspring survival decreased with increasing parent lifespan; parents that ultimately had long lifespans produced offspring that survived poorly, even when these parents were breeding at young ages. 5. The average decrease in offspring survival with increasing parent age observed across the population therefore reflected the gradual disappearance of short-lived parents that produced offspring that survived well, not age-specific variation in offspring survival within individual parents. 6. The negative correlation between offspring survival and maternal lifespan was strongest when environmental conditions meant that offspring survival was low across the population. 7. These data suggest an environment-dependent trade-off between parent and offspring survival, show consistent individual variation in the resolution of this trade-off that is set early in a parent's life, and demonstrate that such structured life-history variation can generate spurious evidence of senescence in key fitness components when measured across a population.
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Affiliation(s)
- Jane M Reid
- Institute of Biological & Environmental Sciences, Zoology Building, University of Aberdeen, Tillydrone Avenue, Aberdeen, UK
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Wasser DE, Sherman PW. Avian longevities and their interpretation under evolutionary theories of senescence. J Zool (1987) 2010. [DOI: 10.1111/j.1469-7998.2009.00671.x] [Citation(s) in RCA: 74] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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Goheen JR, Palmer TM, Keesing F, Riginos C, Young TP. Large herbivores facilitate savanna tree establishment via diverse and indirect pathways. J Anim Ecol 2009; 79:372-82. [PMID: 20039982 DOI: 10.1111/j.1365-2656.2009.01644.x] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
1. Savanna ecosystems are defined largely by tree-grass mixtures, and tree establishment is a key driver of community structure and ecosystem function in these systems. The factors controlling savanna tree establishment are understudied, but likely involve some combination of seed, microsite and predator/fire limitation. In African savannas, suppression and killing of adult trees by large mammals like elephants (Loxodonta africana Blumenbach, 1797) and giraffes (Giraffa camelopardalis Linnaeus, 1758) can maintain tree-grass co-dominance, although the impacts of even these conspicuous herbivores on tree establishment also are poorly understood. 2. We combined seed addition and predator exclusion experiments with a large-scale, long-term field manipulation of large herbivores to investigate the relative importance of seeds, microsites and predators in limiting establishment of a monodominant tree (Acacia drepanolobium Sjostedt) in a Kenyan savanna. 3. Both wild and domestic (i.e. cattle; Bos taurus Linnaeus, 1758) large herbivores facilitated tree establishment by suppressing abundances of rodents, the most important seed and seedling predators. However, this indirect, positive effect of wild herbivores was negated by wild herbivores' suppression of seed production. Cattle did not have this direct, negative impact; rather, they further assisted tree establishment by reducing cover of understorey grasses. Thus, the impacts of both groups of large herbivores on tree establishment were largely routed through other taxa, with a negligible net effect of wild herbivores and a positive net effect of cattle on tree establishment. 4. The distinction between the (positive) net effect of cattle and (neutral) net effect of wild herbivores is due to the inclusion of browsers and mixed feeders within the assemblage of wild herbivores. Browsing by wild herbivores limited seed production, which reduced tree recruitment; grazing by cattle was more pronounced than that by wild herbivores, and thus promoted germination and subsequent establishment of small trees. 5. Our study is the first to link seed fates to tree establishment in savanna ecosystems in experimentally-manipulated herbivore communities. Further, our results highlight how large herbivores can modify a suite of independent factors - seed production, competition with understorey species, and seed and seedling predation - to collectively drive tree establishment.
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Affiliation(s)
- Jacob R Goheen
- Department of Zoology and Biodiversity Research Centre, University of British Columbia, Vancouver, BC V6T 1Z4, Canada.
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Zuidema PA, Brienen RJW, During HJ, Güneralp B. Do persistently fast-growing juveniles contribute disproportionately to population growth? A new analysis tool for matrix models and its application to rainforest trees. Am Nat 2009; 174:709-19. [PMID: 19778168 DOI: 10.1086/605981] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Plants and animals often exhibit strong and persistent growth variation among individuals within a species. Persistently fast-growing individuals have a higher chance of reaching reproductive size, do so at a younger age, and therefore contribute disproportionately to population growth (lambda). Here we introduce a new approach to quantify this "fast-growth effect." We propose using age-size-structured matrix models in which persistently fast and slow growers are distinguished as they occur in relatively young and old age classes for a given size category. Life-cycle pathways involving fast growth can then be identified, and their contribution to lambda is quantified through loop analysis. We applied this approach to an example species, the tropical rainforest tree Cedrela odorata, that shows persistent growth variation among individuals. Loop analysis showed that juvenile trees reaching the 10-cm diameter class at below-median age contributed twice as much to lambda as slow juvenile growers. Fast growth to larger-diameter categories also contributed disproportionately to lambda. The results were robust to changes in parameter values and life-history trade-offs. These results show that the fast-growth effect can be strong in long-lived species. Persistent growth differences among individuals should therefore be accommodated for in demographic models and life-history studies.
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Affiliation(s)
- Pieter A Zuidema
- Ecology and Biodiversity, Institute of Environmental Biology, Utrecht University, P.O. Box 80084, 3508 TB Utrecht, The Netherlands.
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Aubry LM, Koons DN, Monnat JY, Cam E. Consequences of recruitment decisions and heterogeneity on age-specific breeding success in a long-lived seabird. Ecology 2009; 90:2491-502. [PMID: 19769127 DOI: 10.1890/08-1475.1] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
An individual's age at first reproduction and investment in successive reproductive attempts are involved in mechanisms that can impede somatic repair, resulting in a decline in reproductive abilities with age (reproductive senescence). We used long-term data from the Black-legged Kittiwake, a long-lived seabird, to address the relationship between recruitment age, age-specific breeding success (BS), and reproductive senescence, while accounting for breeding experience and temporal variation in BS. We first detected late-life improvement in BS across all recruitment groups, which we recognized as "within-generation selection" or the selective disappearance of "frail" phenotypes. When such heterogeneity was accurately accounted for, we showed that all individuals suffered reproductive senescence. We first highlighted how different combinations of pre- and post-recruitment experience across recruitment groups resulted in maximal BS at intermediate ages. BS increased in early recruits as they gained post-recruitment experience, whereas late recruits gained pre-recruitment experience that led to high BS at recruitment. Only individuals recruiting at intermediate ages balanced their pre- and post-recruitment experience. Consistent with the "cumulative reproductive cost hypothesis," we also observed a faster decline in BS in early recruits at advanced ages, whereas individuals delaying recruitment experienced the slowest decline in BS with age. Early recruits, however, reached the highest levels of BS at intermediate ages, sensus stricto (10-13 years old), whereas individuals delaying recruitment experienced the lowest at similar ages. These divergent trajectories may reflect a "delayed trade-off" balancing a maximization of midlife BS against reproductive senescence at advanced ages. Additionally, annual variation in BS had a greater effect on individuals early in life, suggesting that experienced individuals were able to buffer out the effects of temporal variation on BS, which can ultimately improve fitness in stochastic environments. Our findings stress that (1) both observed and unobserved heterogeneity are important in detecting within-individual senescence, and (2) short-term trade-offs may be rare in long-lived species; thus, cumulated reproductive costs should be invoked as an alternative mechanism underlying reproductive senescence.
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Affiliation(s)
- Lise M Aubry
- Max Planck Institute for Demographic Research, Konrad-Zuse Str. 1, D-18057 Rostock, Germany.
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Ma Z(S, Bechinski EJ. A survival-analysis-based simulation model for Russian wheat aphid population dynamics. Ecol Modell 2008. [DOI: 10.1016/j.ecolmodel.2008.04.011] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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Melbourne BA, Hastings A. Extinction risk depends strongly on factors contributing to stochasticity. Nature 2008; 454:100-3. [PMID: 18596809 DOI: 10.1038/nature06922] [Citation(s) in RCA: 278] [Impact Index Per Article: 17.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2007] [Accepted: 03/13/2008] [Indexed: 11/09/2022]
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35
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Nussey DH, Coulson T, Festa-Bianchet M, Gaillard JM. Measuring senescence in wild animal populations: towards a longitudinal approach. Funct Ecol 2008. [DOI: 10.1111/j.1365-2435.2008.01408.x] [Citation(s) in RCA: 308] [Impact Index Per Article: 19.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Pettorelli N, Durant SM. Family effects on early survival and variance in long-term reproductive success of female cheetahs. J Anim Ecol 2007; 76:908-14. [PMID: 17714269 DOI: 10.1111/j.1365-2656.2007.01266.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
1. While it is generally accepted that the survival of offspring within families may be correlated, the extent of correlation has been largely untested. Furthermore, the impact of such correlation on the estimated variance in females' reproductive success has rarely been quantified. 2. Here we use an exceptional data set from a long-term study of individually recognized cheetahs from the Serengeti National Park in Tanzania to formally quantify family effects in carnivores. 3. We show (i) that cubs from the same litter exhibit more similar fates than unrelated cubs when it comes to first-year survival; and (ii) that the observed variance of the long-term reproductive success of females is twice the variance expected under the assumption of complete independence of fates between cubs. 4. We suggest that family effects are likely to be widespread in vertebrates with average litter sizes > 1, and could have important consequences for population dynamics and population viability analyses.
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Affiliation(s)
- Nathalie Pettorelli
- The Zoological Society of London, Institute of Zoology, Regent's Park, London NW1 4RY, UK.
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