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Pereira AC, Nardoto GB, Colli GR. Sources of intraspecific variation in the isotopic niche of a semi-aquatic predator in a human-modified landscape. PeerJ 2023; 11:e15915. [PMID: 37663285 PMCID: PMC10474837 DOI: 10.7717/peerj.15915] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2022] [Accepted: 07/26/2023] [Indexed: 09/05/2023] Open
Abstract
Intraspecific variation modulates patterns of resource use by species, potentially affecting the structure and stability of food webs. In human-modified landscapes, habitat disturbance modifies trophic interactions and intraspecific niche variation, impacting population persistence. Here, we investigated the relationship of sex, ontogeny, and habitat factors with the trophic niche of Caiman crocodilus in an agricultural landscape. We evaluated temporal variation in the trophic niche parameters using carbon and nitrogen stable isotope analysis from different body tissues. We found that caimans exploit the same carbon and nitrogen pools through time, with low isotopic variability between seasons, partly due to the slow isotope turnover rates of tissues in crocodilians. Conversely, the trophic niche of caimans varied across habitats, but with no evidence of a difference between natural and anthropogenic habitats. It apparently results from the influence of habitat suitability, connectivity, and caiman movements during the foraging. Our findings highlight the broader niches of juvenile caimans relative to adults, possibly in response of territorialism and opportunistic foraging strategy. Although using similar resources, females had a larger niche than males, probably associated with foraging strategies during nesting. Considering the sex and body size categories, caimans occupied distinct isotopic regions in some habitats, indicating apparent niche segregation. Ontogenetic trophic shifts in the isotopes (δ13C and δ15N) depended on sex, leading to resource partitioning that can potentially reduce intraspecific competition. Decision-makers and stakeholders should consider the trophic dynamics of sex and body size groups for the sustainable management and conservation of caiman populations, which implies in the maintenance of wetland habitats and landscape heterogeneity in the Formoso River floodplain.
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Affiliation(s)
- André Costa Pereira
- Departamento de Zoologia, Instituto de Ciências Biológicas, Universidade de Brasília, Brasilia, Distrito Federal, Brazil
- Departamento de Ecologia, Instituto de Ciências Biológicas, Universidade de Brasília, Brasilia, Distrito Federal, Brazil
| | - Gabriela Bielefeld Nardoto
- Departamento de Ecologia, Instituto de Ciências Biológicas, Universidade de Brasília, Brasilia, Distrito Federal, Brazil
| | - Guarino Rinaldi Colli
- Departamento de Zoologia, Instituto de Ciências Biológicas, Universidade de Brasília, Brasilia, Distrito Federal, Brazil
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Lamar SK, Altobelli JT, Nelson NJ, Ormsby DK. Investigating the link between morphological characteristics and diet in an island population of omnivorous reptiles (Sphenodon punctatus). Biol Open 2022; 11:277379. [PMID: 36239241 PMCID: PMC9581517 DOI: 10.1242/bio.059393] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2022] [Accepted: 09/20/2022] [Indexed: 11/20/2022] Open
Abstract
The morphological characteristics that impact feeding ecology in ectotherms, particularly reptiles, are poorly understood. We used morphometric measures and stable isotope analysis (carbon-13 and nitrogen-15) to assess the link between diet and functional morphology in an island population of an evolutionarily unique reptile, the tuatara (Sphenodon punctatus). First, we established a significant positive correlation between overall body size, gape size, and fat store in tuatara (n=56). Next, we describe the relationship between stable isotope profiles created from whole blood and nail trim samples and demonstrate that nail trims offer a low-impact method of creating a long-term dietary profile in ectotherms. We used nitrogen-15 values to assess trophic level in the population and found that tuatara on Takapourewa forage across multiple trophic levels. Finally, we found a significant relationship between gape size and carbon-13 (linear regression: P<0.001), with tuatara with large gapes showing dietary profiles that suggest a higher intake of marine (seabird) prey. However, whether body size or gape size is the primary adaptive characteristic allowing for more optimal foraging is yet unknown. This article has an associated First Person interview with the first author of the paper.
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Affiliation(s)
- Sarah K Lamar
- School of Biological Sciences, Victoria University of Wellington, Wellington 6012, New Zealand.,Center for Biodiversity and Restoration Ecology, Victoria University of Wellington, Wellington 6012, New Zealand
| | | | - Nicola J Nelson
- School of Biological Sciences, Victoria University of Wellington, Wellington 6012, New Zealand.,Center for Biodiversity and Restoration Ecology, Victoria University of Wellington, Wellington 6012, New Zealand
| | - Diane K Ormsby
- School of Biological Sciences, Victoria University of Wellington, Wellington 6012, New Zealand
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Woodborne S, Botha H, Huchzermeyer D, Myburgh J, Hall G, Myburgh A. Ontogenetic dependence of Nile crocodile (Crocodylus niloticus) isotope diet-to-tissue discrimination factors. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2021; 35:e9159. [PMID: 34224610 DOI: 10.1002/rcm.9159] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/20/2021] [Revised: 06/25/2021] [Accepted: 06/27/2021] [Indexed: 06/13/2023]
Abstract
RATIONALE The diet of wild Nile crocodiles (Crocodylus niloticus) is difficult to assess because they are cryptic and nocturnal predators that are extremely sensitive to disturbance by observers, and stomach content analysis is challenging, especially in large specimens. Stable light isotope analysis provides a means of assessing their diet, but diet-to-tissue discrimination factors have yet to be established for the species. METHODS Isotope ratio (15 N/14 N and 13 C/12 C expressed as δ15 N and δ13 C) analyses of scutes, claws, and blood of farmed crocodiles of different sizes were compared with the isotope values of their lifelong diet, which comprises chickens from a single supplier. RESULTS Systematic size dependence in the diet-to-tissue discrimination factors for scute collagen, scute keratin, and claw keratin is described in regression relationships against the snout to vent length. Fixed values are presented for erythrocytes and blood plasma because blood was not sampled from juveniles. CONCLUSIONS The diet-to-tissue discrimination factors help assess the diet of wild crocodiles. The diet of crocodiles from Lake Flag Boshielo shows a clear ontogenic shift, as has been seen in other studies, and the results strongly indicate a dependence on the terrestrial food web rather than a fish diet. That this population may exploit a terrestrial diet highlights potential conflicts for conserving Nile crocodiles outside protected areas.
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Affiliation(s)
- Stephan Woodborne
- Tandem & AMS Laboratory, iThemba LABS, Johannesburg, South Africa
- Stable Isotope Laboratory, Mammal Research Institute, University of Pretoria, Pretoria, South Africa
| | - Hannes Botha
- Mpumalanga Tourism and Parks Agency, Scientific Services, Nelspruit, South Africa
- Department of Biodiversity, University of Limpopo, Sovenga, South Africa
| | | | - Jan Myburgh
- Department of Paraclinical Sciences, Faculty of Veterinary Science, University of Pretoria, Onderstepoort, South Africa
| | - Grant Hall
- Stable Isotope Laboratory, Mammal Research Institute, University of Pretoria, Pretoria, South Africa
| | - Albert Myburgh
- Department of Zoology and Entomology, University of Pretoria, Pretoria, South Africa
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Hamilton MT, Finger JW, Elsey RM, Mastromonaco GF, Tuberville TD. Corticosterone in American alligator (Alligator mississippiensis) tail scutes: Evaluating the feasibility of using unconventional samples for investigating environmental stressors. Gen Comp Endocrinol 2018; 268:7-13. [PMID: 30031024 DOI: 10.1016/j.ygcen.2018.07.008] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/09/2018] [Revised: 06/23/2018] [Accepted: 07/13/2018] [Indexed: 12/31/2022]
Abstract
Baseline plasma corticosterone (CORT) concentrations have been widely used to investigate the effects of stressors in wild and captive crocodilians. However, collecting baseline plasma CORT samples from wild crocodilians may be particularly difficult due to the capture and handling protocols used for large individuals. Thus, it may prove beneficial to use recently modified techniques for extracting CORT deposited in keratinized and non-keratinized tissues to better quantify the effects of long-term stress in crocodilians. In this study, we investigated the feasibility of using American alligator (Alligator mississippiensis) tail scute tissues to quantify CORT by collecting blood and tail scutes from 40 alligators before and after a short-term handling stressor. The objective of the current study was to better understand CORT deposition in crocodilian scutes and whether short-term increases in CORT could be detected. We found that CORT can be reliably extracted from alligator scute tissue and quantified using a commercially available enzyme immunoassay. However, there was a significant increase in scute CORT concentrations following an alligator being exposed to a short-term stressor (p = 0.017), although the magnitude of change was less than observed in plasma samples from the same individuals (p = 0.002). Furthermore, our results indicate that there was a significant effect of body condition on an alligator's post-stressor CORT concentration (p = 0.02). While our study is among the first to experimentally examine the usefulness of tissue CORT in crocodilians, a combination of field and laboratory experiments are needed to better understand deposition rates of CORT in scute tissues and to further validate the usefulness of tissue glucocorticoids for evaluating the effects of stress.
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Affiliation(s)
- Matthew T Hamilton
- Savannah River Ecology Laboratory, University of Georgia, Aiken, SC 29802, USA.
| | - John W Finger
- Savannah River Ecology Laboratory, University of Georgia, Aiken, SC 29802, USA; Department of Environmental Health Science, University of Georgia, Athens, GA 30602, USA
| | - Ruth M Elsey
- Louisiana Department of Wildlife and Fisheries, Rockefeller Wildlife Refuge, Grand Chenier, LA 70643, USA
| | | | - Tracey D Tuberville
- Savannah River Ecology Laboratory, University of Georgia, Aiken, SC 29802, USA
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Estuarine crocodiles in a tropical coastal floodplain obtain nutrition from terrestrial prey. PLoS One 2018; 13:e0197159. [PMID: 29874276 PMCID: PMC5991389 DOI: 10.1371/journal.pone.0197159] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2017] [Accepted: 04/27/2018] [Indexed: 11/23/2022] Open
Abstract
The estuarine crocodile (Crocodylus porosus) is one of the largest and most widespread crocodilians in the world. Although considered an apex species, the role of the estuarine crocodile in aquatic foodwebs is poorly understood; we know what crocodiles ingest, but not what nourishes them. In this study, we used a combination of stable isotope measurements (δ13C, δ15N, and δ34S) and direct feeding observations to identify the source of nutrition of estuarine crocodiles in Kakadu National Park, Northern Australia. Our results show that most crocodiles sampled (size 850 – 4200mm, with 76% of them being > 2.5 m) consume a large variety of prey, however a large proportion of their nutrition is derived from terrestrial prey. Introduced species such as water buffaloes (Bubalus bubalis) and pigs (Sus scrofa) could contribute between 53 and 84% to the nutrition of the sampled crocodiles. The isotopic composition of large crocodiles (total length > 3 m) suggested possible increase in marine prey consumption with size (R2 = 0.30; p = 0.005). Additionally, we found crocodiles sampled in the dry season had on average higher terrestrial contributions compared to crocodiles sampled during the wet season (84.1 ± 2.4% versus 55.4 ± 7.0%). Overall, we found that terrestrial prey are important source of nutrition for many crocodiles in this region where introduced herbivorous mammals are abundant.
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Villamarín F, Jardine TD, Bunn SE, Marioni B, Magnusson WE. Body size is more important than diet in determining stable-isotope estimates of trophic position in crocodilians. Sci Rep 2018; 8:2020. [PMID: 29386654 PMCID: PMC5792559 DOI: 10.1038/s41598-018-19918-6] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2017] [Accepted: 01/04/2018] [Indexed: 11/25/2022] Open
Abstract
The trophic position of a top predator, synonymous with food-chain length, is one of the most fundamental attributes of ecosystems. Stable isotope ratios of nitrogen (δ15N) have been used to estimate trophic position of organisms due to the predictable enrichment of 15N in consumer tissues relative to their diet. Previous studies in crocodilians have found upward ontogenetic shifts in their 'trophic position'. However, such increases are not expected from what is known about crocodilian diets because ontogenetic shifts in diet relate to taxonomic categories of prey rather than shifts to prey from higher trophic levels. When we analysed dietary information from the literature on the four Amazonian crocodilians, ontogenetic shifts in dietary-based trophic position (TPdiet) were minimal, and differed from those estimated using δ15N data (TPSIA). Thus, ontogenetic shifts in TPSIA may result not only from dietary assimilation but also from trophic discrimination factors (TDF or Δ 15N) associated with body size. Using a unique TDF value to estimate trophic position of crocodilians of all sizes might obscure conclusions about ontogenetic shifts in trophic position. Our findings may change the way that researchers estimate trophic position of organisms that show orders of magnitude differences in size across their life span.
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Affiliation(s)
- Francisco Villamarín
- Coordenação de Pesquisas em Biodiversidade, Instituto Nacional de Pesquisas da Amazônia - INPA, Manaus, Brazil.
- Universidad Regional Amazónica - Ikiam, Tena, Ecuador.
| | - Timothy D Jardine
- School of Environment and Sustainability, University of Saskatchewan, Saskatoon, Canada
| | - Stuart E Bunn
- Australian Rivers Institute, Griffith University, Brisbane, Australia
| | - Boris Marioni
- Programa de Pós-Graduação em Biologia de Água Doce e Pesca Interior - INPA, Manaus, Brazil
| | - William E Magnusson
- Coordenação de Pesquisas em Biodiversidade, Instituto Nacional de Pesquisas da Amazônia - INPA, Manaus, Brazil
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Holá M, Ježek M, Kušta T, Košatová M. Trophic discrimination factors of stable carbon and nitrogen isotopes in hair of corn fed wild boar. PLoS One 2015; 10:e0125042. [PMID: 25915400 PMCID: PMC4411150 DOI: 10.1371/journal.pone.0125042] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2014] [Accepted: 03/09/2015] [Indexed: 11/24/2022] Open
Abstract
Stable isotope measurements are increasingly being used to gain insights into the nutritional ecology of many wildlife species and their role in ecosystem structure and function. Such studies require estimations of trophic discrimination factors (i.e. differences in the isotopic ratio between the consumer and its diet). Although trophic discrimination factors are tissue- and species- specific, researchers often rely on generalized, and fixed trophic discrimination factors that have not been experimentally derived. In this experimental study, captive wild boar (Sus scrofa) were fed a controlled diet of corn (Zea mays), a popular and increasingly dominant food source for wild boar in the Czech Republic and elsewhere in Europe, and trophic discrimination factors for stable carbon (Δ13C) and nitrogen (Δ15N) isotopes were determined from hair samples. The mean Δ13C and Δ15N in wild boar hair were –2.3 ‰ and +3.5 ‰, respectively. Also, in order to facilitate future derivations of isotopic measurements along wild boar hair, we calculated the average hair growth rate to be 1.1 mm d-1. Our results serve as a baseline for interpreting isotopic patterns of free-ranging wild boar in current European agricultural landscapes. However, future research is needed in order to provide a broader understanding of the processes underlying the variation in trophic discrimination factors of carbon and nitrogen across of variety of diet types.
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Affiliation(s)
- Michaela Holá
- Department of Game Management and Wildlife Biology, Faculty of Forestry and Wood Sciences, Czech University of Life Sciences Prague, Prague, Czech Republic
- * E-mail:
| | - Miloš Ježek
- Department of Game Management and Wildlife Biology, Faculty of Forestry and Wood Sciences, Czech University of Life Sciences Prague, Prague, Czech Republic
| | - Tomáš Kušta
- Department of Game Management and Wildlife Biology, Faculty of Forestry and Wood Sciences, Czech University of Life Sciences Prague, Prague, Czech Republic
| | - Michaela Košatová
- Department of Ecology, Faculty of Environmental Sciences, Czech University of Life Sciences Prague, Prague, Czech Republic
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Nifong JC, Layman CA, Silliman BR. Size, sex and individual-level behaviour drive intrapopulation variation in cross-ecosystem foraging of a top-predator. J Anim Ecol 2014; 84:35-48. [PMID: 25327480 DOI: 10.1111/1365-2656.12306] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2014] [Accepted: 10/07/2014] [Indexed: 11/28/2022]
Abstract
Large-bodied, top-predators are often highly mobile, with the potential to provide important linkages between spatially distinct food webs. What biological factors contribute to variation in cross-ecosystem movements, however, have rarely been examined. Here, we investigated how ontogeny (body size), sex and individual-level behaviour impacts intrapopulation variation in cross-ecosystem foraging (i.e. between freshwater and marine systems), by the top-predator Alligator mississippiensis. Field surveys revealed A. mississippiensis uses marine ecosystems regularly and are abundant in estuarine tidal creeks (from 0·3 to 6·3 individuals per km of creek, n = 45 surveys). Alligator mississippiensis captured in marine/estuarine habitats were significantly larger than individuals captured in freshwater and intermediate habitats. Stomach content analysis (SCA) showed that small juveniles consumed marine/estuarine prey less frequently (6·7% of individuals) than did large juveniles (57·8%), subadult (73%), and adult (78%) size classes. Isotopic mixing model analysis (SIAR) also suggests substantial variation in use of marine/estuarine prey resources with differences among and within size classes between sexes and individuals (range of median estimates for marine/estuarine diet contribution = 0·05-0·76). These results demonstrate the importance of intrapopulation characteristics (body size, sex and individual specialization) as key determinants of the strength of predator-driven ecosystem connectivity resulting from cross-ecosystem foraging behaviours. Understanding the factors, which contribute to variation in cross-ecosystem foraging behaviours, will improve our predictive understanding of the effects of top-predators on community structure and ecosystem function.
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Affiliation(s)
- James C Nifong
- Department of Biology, University of Florida, Gainesville, FL, USA
| | - Craig A Layman
- Department of Applied Ecology, North Carolina State University, Chapel Hill, NC, USA
| | - Brian R Silliman
- Division of Marine Sciences and Conservation, Nicholas School of the Environment, Duke University, Beaufort, NC, USA
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