Quantifying Diets of Wildlife and Fish: Practical and Applied Methods

Quantifying Diets of Wildlife and Fish presents different techniques available to study animal diets. Ecologists determine animal diets to build natural history knowledge, test hypotheses in ecological theory and make informed management decisions for important ecosystems. Many researchers use techniques traditionally applied to the animals they study, rather than techniques with the greatest potential for the aims of each project. In an effort to encourage researchers to consider new approaches, this book focuses on the techniques, rather than on particular groups of organisms or specific environments.

With contributions from leading ecologists, chapters explore experimental design, observational techniques (including new technologies), stomach contents and faecal analysis, eDNA, tracers and stable isotopes. They also cover the latest multivariate methods of analyses suitable for describing animal diets and feeding relationships, as well as testing hypotheses relevant to ecological theory, environmental management and biological conservation. The expert knowledge provided will encourage readers to look beyond the boundaries of their specialties, assist in testing important hypotheses and provide insights into management problems. The examples in this book cover a range of vertebrates and invertebrates, as well as different environments, to open these methods up for novice ecologists and stimulate lateral thinking in more experienced researchers.

• Language: English
• Publisher: CSIRO PUBLISHING
• Release date: May 1, 2024
• ISBN: 9781486315024

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Quantifying Diets of Wildlife and Fish

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Contents

Preface

Michael C. Calver and Neil R. Loneragan

About the editors

List of contributors

1Why and how should we study animal diets?

Michael C. Calver, Neil R. Loneragan, Margaret E. Platell, Matthew W. Hayward and James R. Tweedley

2Applying natural history field observations to describing animal foraging behaviour

Harry F. Recher and Michael C. Calver

3Stomach content analysis

Ronald Baker, Heather M. Crawford and Marcus Sheaves

4Faecal analysis

Patricia A. Fleming and Natalie K. Grassi

5Metabarcoding to assess animal diets

Haruko Ando

6Diet tracers in food webs: fatty acids and their carbon and hydrogen stable isotopes

Martin J. Kainz, Matthias Pilecky and Fen Guo

7Stable isotope analysis

Kátya Abrantes and Marcus Sheaves

8Field experiments on foragers, food and their interactions

Christopher R. Dickman

9Demystifying multivariate approaches for analysing dietary data

Margaret E. Platell, Matthew W. Hayward and James R. Tweedley

10 Where to from here in the study of animal diets?

Michael C. Calver and Neil R. Loneragan

Index of common names

Index of scientific names

Index of topics

Preface

Michael C. Calver and Neil R. Loneragan

Our first scientific publications, in the early 1980s, were on feeding ecology – Mike’s on the foods of small birds in the understorey of Western Australia’s karri forests (a hobby project alongside his main research on grasshoppers), and Neil’s on diet and feeding segregation of atherinid fish in south-western Australian estuaries. At the time very little was known of the foods of either the karri forest birds or the estuarine atherinids, so these were just the topics for beginning research students. Although both studies presented new natural history data, they also developed ecological understanding and had implications for the management of the respective ecosystems. There was debate over the effects of logging and burning on the ecology of karri forest animals, as well as the functioning of estuarine food webs and development of quantitative ecosystem models for the management of estuaries for fishing and biological conservation.

Today, ecologists still need to determine animal diets for reasons that include building natural history knowledge, testing hypotheses in ecological theory and making informed management decisions for important ecosystems, which are goals unchanged from those of our early work. Similarly, some methods of collecting the relevant data have endured, while others have been updated or superseded. Mike determined the foods of the karri birds by examining their droppings and Neil analysed data on the stomach contents of the atherinids collected by a co-author. Those techniques had a long history of use by the time we applied them and they are still applied extensively today. The same is true of the statistical analytical techniques, such as analysis of variance, diet diversity, diet overlap and correlation coefficients, we used in the early 1980s and are still applied in contemporary studies. Not all techniques have endured, though. The immunological techniques Mike applied later in the 1980s went some way to addressing the problem of unidentifiable sludge in stomach contents or the liquid foods ingested by many invertebrates, but the advances in chemical and genetic techniques developed this century have largely supplanted them. Similarly, although many statistical techniques relevant to analysing dietary data have endured, increases in computing power have enabled a wide range of sophisticated multivariate analyses to complement the more traditional univariate tests. In combination, these developments complement traditional dietary studies to understand the structure and function of food webs.

From our differing perspectives as terrestrial and aquatic ecologists, we have also noted that many researchers specialise in a small group of organisms or a system and, as a result, may be unaware of developments that occur elsewhere that are applicable to their specialist fields. For example, fisheries biologists have grappled with different methods to quantify the stomach contents of animals for dietary work, as well as with multivariate statistical techniques to analyse diets and communities. In our experience, terrestrial ecologists, despite their impressive record of experimental work and associated analyses, have been either unaware of some of these innovations or slow to adapt them to new contexts.

These observations led us to the concept for this book. Ecologists still document natural history as a background to intelligent hypothesis testing and ecosystem management, but we believe there is a need to focus on the different techniques available to study animal diets, rather than on particular groups of organisms or specific environments. If, in the coverage of each technique, examples are given from a range of vertebrates and invertebrates, as well as different environments, ecologists might look beyond the boundaries of their specialties and perhaps consider new approaches that would assist in testing important hypotheses, or providing insights into management problems. Fortunately, many experienced ecologists were keen to contribute to the project and write chapters that focused on a technique, not an environment or a group of animals, and thus open the black boxes of these methods for beginning ecologists and more experienced researchers considering a change of direction.

We are grateful to all the contributing authors for their expertise, patience and sheer hard work in bringing each chapter to completion. We thank Paul Boon, Carla Catterall, Chris Dickman, Hugh Ford, Claire Greenwell, Ric How and Thea Linke for their assistance in reviewing chapters for clarity and accessibility to non-specialist readers; their insights greatly improved editorial feedback to authors. Belinda Cale ably dealt with the challenges of converting several figures prepared originally in colour to greyscale for publication. The people at CSIRO Publishing, including Tracey Kudis, Eloise Moir-Ford, Mark Hamilton and Briana Melideo, and freelance editor Kerry Brown were patient and helpful in guiding us through the editorial process amid the twists and surprises of the COVID and post-COVID eras.

About the editors

MICHAEL C. CALVER

Emeritus Professor Michael Calver is based in the School of Environmental and Conservation Sciences, as well as the Centre for Terrestrial Ecosystem Science and Sustainability in the Harry Butler Institute at Murdoch University. He is best described as a frustrated entomologist, because after studying grasshoppers for his PhD he discovered quickly that prospective research students wanted to study mainly mammals, with birds as a reluctant second choice. Thus, he became a de facto wildlife biologist, with insects only entering the picture as food for ‘real’ animals. The feeding connection led to an interest in describing animal diets, which in turn led to the conception of this book.

NEIL R. LONERAGAN

Emeritus Professor Neil Loneragan is also based in the School of Environmental and Conservation Sciences and the Harry Butler Institute at Murdoch University and is an adjunct Professor at IBP University in Indonesia. He is best described as a fish ecologist, with interests in understanding marine and estuarine food webs, fisheries dynamics and the application of ecological principles to evaluating fish stock enhancement and marine ranching. Characterising diets and the food assimilated by species in different aquatic systems is a core part of his research interests and those of his students, which has led to collaborative research on stomach contents, stable isotopes, fatty acids and ecosystem modelling. The central role of understanding diet and feeding meant he leapt at the chance to develop this book with MC.

List of contributors

Abrantes, Kátya. Research Fellow, Biopixel Oceans Foundation, Cairns; College of Science and Engineering, James Cook University. [e-mail]

Ando, Haruko. Senior Researcher, Biodiversity Division, National Institute for Environmental Studies, Japan. [e-mail]

Baker, Ronald. Assistant Professor, School of Marine and Environmental Sciences, University of South Alabama; Dauphin Island Sea Lab, Alabama. [e-mail]

Calver, Michael. Emeritus Professor, School of Environmental and Conservation Sciences, Murdoch University. [e-mail]

Crawford, Heather. Animal Biology Laboratory Technician, School of Environmental and Conservation Sciences, Murdoch University. [e-mail]

Dickman, Christopher. Professor in Ecology, Desert Ecology Research Group, School of Life and Environmental Sciences, The University of Sydney. [e-mail]

Fleming, Patricia (Trish). Professor in Wildlife Conservation, Centre for Terrestrial Ecosystem Science and Sustainability, Harry Butler Institute, Murdoch University. [e-mail]

Grassi, Natalie. PhD candidate, School of Environmental and Conservation Sciences, Murdoch University. [e-mail]

Guo, Fen. Professor, School of Ecology, Environment and Resources, Guangdong University of Technology, China. [e-mail]

Hayward, Matthew. Professor, School of Environmental and Life Sciences, University of Newcastle, Australia; Centre for African Conservation Ecology, Nelson Mandela University, South Africa. [e-mail]

Kainz, Martin. Professor, WasserCluster – Biologische Station Lunz, Austria. [e-mail]

Loneragan, Neil. Professor Emeritus, School of Environmental and Conservation Sciences and Harry Butler Institute, Murdoch University. [e-mail]

Pilecky, Matthias. Postdoctoral Researcher, WasserCluster – Biologische Station Lunz, Austria; Danube University Krems. [e-mail]

Platell, Margaret. Lecturer, School of Environmental and Life Sciences, University of Newcastle, Australia. [e-mail]

Recher, Harry. Senior Fellow, Australian Museum Research Institute; Adjunct, School of Environmental and Conservation Sciences, Murdoch University. [e-mail]

Sheaves, Marcus. Professor, College of Science and Engineering, James Cook University; Marine Data Technology Hub, James Cook University. [e-mail]

Tweedley, James. Senior Lecturer, Centre for Sustainable Aquatic Ecosystems, Harry Butler Institute, Murdoch University; Environmental and Conservation Sciences, Murdoch University. [e-mail]

1Why and how should we study animal diets?

Michael C. Calver, Neil R. Loneragan, Margaret E. Platell, Matthew W. Hayward and James R. Tweedley

INTRODUCTION

Over 100 years ago, McAtee (1912) set out to settle once and for all the debate on whether data on the contents of animal stomachs should be presented as percentage-by-bulk (the volume of each prey type; percentage volume or volumetric percentage) or numerically (based on counts of the number of individuals in each food type; numerical percentage). He didn’t succeed, with numerous other authors, including Pinkas et al. (1971) and Hart et al. (2002), also considering the question many years later. Indices combining multiple methods were proposed, while others argued strongly for presentation of the different methods individually to facilitate combining data across multiple studies in meta-analyses (Buckland et al. 2017). The story continues in Chapter 3, where the authors wrestle with the practical problems of identifying foods from stomach contents and quantifying the findings.

The persistence of the debate confirms the ongoing interest in animal diets, acknowledging that there is still much discussion on how best to describe and quantify their important features. In this chapter we first outline the compelling reasons why it is important to study animal diets, grouping them under the themes of natural history, ecosystem function, food selection behaviour and practical applications. We then turn to the question of how to study animal diets, which is the primary focus of the book, explaining how the remaining chapters are structured to answer this question.

WHY STUDY ANIMAL DIETS?

Natural history

Natural history is the study of organisms in their natural environment (Tewksbury et al. 2014). It is sometimes criticised by those who believe that true understanding arises from experimentation (Hairston 1989), although even committed experimentalists must concede that detailed knowledge of natural history is needed to choose the correct subjects and provide context for interpreting experimental results (McKeon et al. 2020). Furthermore, the breeding of animals in captivity, often with the aim of reintroducing them into the wild, benefits from understanding their particular food and nutrition (Hume 2005; Stannard and Old 2011; Lorenzen et al. 2021; Stannard et al. 2021). Insights on natural history come most commonly from studies of animals in the field, although much useful information is contained in museum collections and the associated notes, including collectors’ and explorers’ diaries (Meineke et al. 2019). All of these sources are integral to the correct application and interpretation of all methods used to study animal diets.

Classifying animal diets by the taxa of prey eaten or the diversity of foods consumed

For convenience, animals are often categorised broadly as carnivores, herbivores, omnivores and parasites, with specific subcategories recognised (Table 1.1, Fig. 1.1). This neatness obscures reality. For example, the red fox Vulpes vulpes is regarded as a carnivore and more specifically a faunivore (i.e. generally taken to mean ‘eats vertebrates’, although invertebrates are also fauna), yet it scavenges carcasses, eats invertebrates and even feeds extensively on plant material (Klieve et al. 2015; Castañeda et al. 2022). Similarly, in Australia the common brushtail possum Trichosurus vulpecula is regarded as a herbivore and folivore (i.e. a plant-eater specialising in leaves), yet individuals may eat meat baits intended for introduced predators, reducing the success of baiting intended to protect the possums (Hohnen et al. 2020).

Table 1.1. A natural history classification of animal diets following Hume (2005) , Krebs (2014) and Klieve et al . (2015)

Fig. 1.1. Examples of animal feeding classifications. (a) Carnivores: (left to right) grey heron Ardea cinerea ¹ , Tasmanian devil Sarcophilus harrisi ² , harlequin fish Othos dentex ⁵ . (b) Herbivores: (left to right) greater kudu Tragelaphus strepsiceros ¹ , white rhinoceros Ceratotherium simum ¹ , koala Phascolarctos cinereus ² , luderick Girella tricuspidata ⁶ . (c) Omnivores: (left to right) baboon Papio sp. ¹ , brushtail possum Trichosurus vulpecula (commonly considered a herbivore but known to eat animals as well) ² , tarwhine Rhabdosargus sarba ⁶ . (d) Parasites: (left to right) louse Pediculus humanus ³ , Taenia taeniformis cysticercus in a Rattus rattus liver ⁴ (i.e. an endoparasite), sea lamprey Petromyzon marinus ⁷ (i.e. an ectoparasite). Image credits: ¹ Matt Hayward, ² Jiri Lochman (Lochman Transparencies; https://www.lochmantransparencies.com ), ³ Llewellyn Lloyd under a public domain licence, ⁴ Dr Narelle Amanda Dybing, ⁵ Peter Southwood under a CC BY-SA 3.0 licence, ⁶ Richard Ling under a CC BY-SA 2.0 licence, ⁷ US Fish and Wildlife Service under a public domain licence.

Alternatively, animals may be categorised into generalists (a wide range of food species), specialists (a particular type of food) or opportunists, whose diet closely reflects food availability. Once again, the distinctions between these groupings of convenience may be grey. For example, within the African large predator guild, lions Panthera leo were considered generalist predators of larger prey and cheetahs Acinonyx jubatus as specialists on gazelles (Schaller 1968, 1972). A more nuanced understanding is that all large predators, except the spotted hyaena Crocuta crocuta, preferentially prey on a few species (Hayward and Kerley 2008). Individual studies missed this because of the opportunism inherent within optimal foraging (Charnov 1976; Pyke et al. 1977; Pyke 1984) – individual researchers studying one species at one site observed predators taking a broader suite of prey, simply because an optimally foraging predator opportunistically captures prey outside its preferred/optimal range when capture and handling are energetically beneficial with minimal risk.

Generalist, specialist and opportunist predators are also prevalent within coastal marine and estuarine environments (Greenwell et al. 2019; Ibáñez et al. 2021; Whitfield et al. 2022). All 18 demersal marine fish predators in south-western Australia ingest many prey species and are considered generalists (e.g. Platell and Potter 2001). However, significant dietary differences exist between species, implying that some generalists specialise on particular prey within the broad suite ingested.

Developmental changes in diet and relationships between morphology and feeding

Developmental (ontogenetic) changes in diets occur in fish and aquatic reptile predators, typically associated with increases in the mouth size and swimming ability of the predator as it grows and reflected in shifts from smaller, soft-bodied to larger, more hard-bodied or mobile prey (Werner and Gilliam 1984; Platell and Potter 1998; Sánchez-Hernández et al. 2019). These developmental dietary changes also occur in herbivores (Yiu et al. 2019). Species may specialise on certain foods with increasing body size or perhaps become more generalist, with these changes in diet often linked to specific habitat characteristics. This is also apparent among terrestrial predators. Subadult lions, for example, rely on warthogs Phacochoerus africanus during their nomadic phase, but prefer larger prey as adult members of a territory-holding pride (Hayward and Kerley 2005; Hayward et al. 2007a).

The influence of food availability

Although opportunism in diets of aquatic organisms can be inferred from dietary composition data (e.g. Pedreschi et al. 2015), other studies link temporal dietary changes to prey availability. Thus, there may be a superabundance of prey providing feeding opportunities or there may be an absence of the usual prey (see Fennessy et al. 2010 and Schafer et al. 2002 for marine examples, and Schaller 1972 and Hilderbrand et al. 1999 for terrestrial ones). Herbivores may follow vegetation succession, such as changes in quokka Setonix brachyurus diet following the fire history of the area (Hayward 2005).

Ecosystem function

Animals’ food choices influence nutrient cycling (Ellis et al. 1976), energy transfer between trophic levels (McMahon et al. 2021) and the dispersal of plant or fungal propagules (Dundas et al. 2018; Hopkins et al. 2021). They also drive the structure and function of communities (Peinetti et al. 2009) and underpin key concepts such as optimal foraging (French et al. 2013; Meehan et al. 2022) and niche structure and resource partitioning (Blubaugh et al. 2022), as well as community stability (Pimm 1982; Mougi 2022). Bioturbation, the disturbance of soil by organisms while feeding or burrowing, is a significant example in terrestrial systems (Valentine et al. 2017, 2018). In aquatic systems, the feeding of sea cucumbers (holothurians) has a similar role, which is exploited in polyculture systems of sea cucumbers and other organisms to enhance sustainable aquaculture production (Purcell et al. 2006; Jiang et al. 2017).

Food selection behaviour

Much ecological research seeks to describe or explain how animals choose their food. Hess and Swartz (1940) proposed the forage ratio as the ‘ratio of the percentage which a given kind of organism makes up of the total contents to the percentage which this same organism makes up of the total population of food organisms’ to indicate preference or aversion for different foods depending on their availability in the environment. It remained the primary method of measuring preference until partially refined by Ivlev (1961), but more robust measures took precedence when Manly (1973) developed an intuitive preference index for two or three prey situations (Chesson 1978). This followed advances by Jacobs (1974) and Strauss (1979), who recognised that the forage ratio and Ivlev’s index are biased to rare foods, non-linear, exhibit increasing confidence intervals with increasing heterogeneity, lack symmetry between selected and avoided values, and exhibit increasing error at small proportions (Norbury and Sanson 1992). Jacobs’ index was used to determine the prey preferences of large African predators throughout their distribution by comparing the preference value for each species at each site against a mean of zero, using known weights of likely prey (Hayward and Kerley 2005; Hayward et al. 2006a, b, c; Clements et al. 2014). This research was extended to Eurasian and American predators (Hayward et al. 2012, 2014, 2017; Niedzialkowska et al. 2019) More recently, Nams and Hayward (2022) derived a method of iterative preference averaging for determining prey selection when data on the full community of prey at some sites are incomplete. Although none of the selectivity indices is clearly ‘best’, recent equations minimise biases (Krebs 1989).

Practical applications

Responses to anthropogenic change

Dietary compositions are used to infer changes in response to anthropogenic factors such as climate change (Atlantic cod Gadus morhua over nearly a century – Townhill et al. 2021), habitat loss/change (spiny lobsters in the Caribbean – Briones-Fourzán et al. 2019), farming activities (the Maugean skate Zearaja maugeana in Tasmania – Weltz et al. 2019), introduced species (invasive fish, frogs and freshwater crayfish vs endemic water snakes and frogs – Bissattini et al. 2021) and understanding predators’ responses to management (interactions with other fisheries of G. morhua – Townhill et al. 2021). In terrestrial systems of Africa, the relationship between preferred prey availability and predator densities can be used to identify poaching of those predators, keeping predator populations below carrying capacity when predator densities are below expectations based on the available prey abundances (Hayward et al. 2007b).

Conservation planning

Data on prey preferences can estimate how many predators can be sustained at a site based on the known abundance of prey (carrying capacity – Hayward et al. 2007b); to predict the diet and home range of translocated predators (Hayward 2009). Moreover, such data determine appropriate stocking densities for releasing aquacultured fish into the wild (termed aquaculture-based enhancement) to restore or enhance predator populations (Taylor and Suthers 2008; Taylor et al. 2013). In animal management, knowing species’ prey preferences predicts the likely fate of reintroduced populations, such as large terrestrial African carnivores (Hayward 2009; Louw et al. 2012), or the spatial behaviour of prey following fencing of protected areas (Hayward et al. 2009).

Biological control

Biological control reduces pest numbers using predators, parasites, parasitoids and diseases (Fischbein and Corley 2022). Most commonly, the pests were introduced into the ecosystem, so natural enemies of the pests are identified in their native environment and imported to the new location to contain the pest’s numbers (Zachariades et al. 2022). Biological control has achieved some spectacular successes, such as the introduction of the moth Cactoblastis cactorum and the cochineal insect Dactylopius opuntiae to control prickly pear Opuntia stricta in Queensland, Australia, and also South Africa (Hoffmann et al. 2020) (but see Hunter et al. 2021 for some habitats where biocontrol agents do not establish well). In contrast, there are equally spectacular disasters, such as introducing the cane toad Rhinella marina to control cane beetle in Queensland sugar cane crops, leading to the spread of the toad across Australia where it poisons indigenous predators and competes with native amphibians (Shine et al. 2020).

Ecosystem modelling

Understanding ecosystem function and trophic flows is essential for developing models for determining how systems might change under environmental or anthropogenic impacts. Model development is particularly important in understanding the impacts of fishing, climate change and marine protected areas (e.g. Christensen 1998; Pauly et al. 2002; Fulton et al. 2011; Lozano-Montes et al. 2011, 2012), often using specialist software such as Ecopath with Ecosim (Christensen and Walters 2004).

PURPOSE AND STRUCTURE OF THE BOOK

To address any of the reasons to study animal diets that we have raised requires facility with technical approaches to determine what foods are eaten. Nevertheless, as ecologists working across aquatic and terrestrial systems, we find that researchers of particular taxa or communities often focus on the literature covering only their special interests, delaying the exchange of techniques and innovations that are not intrinsically restricted to particular organisms, ecosystems or situations. In the interests of good communication that crosses taxonomic, disciplinary and community boundaries, this book provides a single-volume introduction to the range of techniques available, synthesising information currently scattered across diverse primary and secondary sources. Each chapter covers a specific technique, with aquatic and terrestrial examples, giving research students and experienced researchers a single source that assesses the merits of different options for their studies from planning, data collection and data processing through to statistical analyses.

Chapter 2 describes observational approaches to studying diets, progressing from general principles to ecological insights gathered from specific examples, concluding with descriptions of the application of new technologies that are greatly extending the range of observations collected and the research questions that can be addressed. Chapter 3 covers another method with a long history in ecology, the analysis of stomach contents from animals to describe their diets. The optimal way to present such data has stimulated much discussion, so the Chapter 3 authors offer suggestions for standardisation that should benefit meta-analyses. Chapter 4 completes the coverage of traditional methods by discussing the use of droppings to determine foods eaten by study animals. Analysis of droppings is often done with little disturbance to the study animals, but offers challenges in relation to the differential digestibility of foods eaten – a point addressed with examples in this chapter.

Chapters 5–7 break new ground in dietary analysis using technical advances in molecular biology over recent decades. Chapter 5 gives a brief history of the development of molecular-based diet analyses, before describing how analyses based on DNA metabarcoding of faecal samples provide a non-invasive and accurate method of determining animal diets. Chapter 6 explores another recent method, the use of fatty acids and carbon and hydrogen stable isotopes, to trace food sources and their conversion within animals after ingestion. In Chapter 7 the work on stable isotopes is expanded, explaining how they provide time- and space-integrated information on the material assimilated by organisms, unlike traditional methods such as direct observation, gut contents and faecal analysis, which provide a snapshot of the material recently ingested (which might not be the same as what is assimilated). Chapter 8 explains how the techniques described in Chapters 2–7 can be incorporated within experimental manipulations of natural systems to answer questions about how animals locate and process food, why they show particular preferences and how these choices influence community structure through the food webs they underpin. In Chapter 9, the question of statistical analyses of the results of dietary studies is explored, with a strong focus on the application of multivariate techniques developed and applied in recent decades. Finally, Chapter 10 explores how techniques to study animal diets may develop in the future.

REFERENCES

Bissattini AM, Haubrock PJ, Buono V, Balzani P, Borgianni N, et al. (2021) Trophic structure of a pond community dominated by an invasive alien species: insights from stomach content and stable isotope analyses. Aquatic Conservation: Marine and Freshwater Ecosystems 31, 948–963. doi:10.1002/aqc.3530

Blubaugh CK, McElvenny AE, Widick IV (2022) Habitat complexity mediates spatiotemporal niche partitioning among native and invasive seed predators. Food Webs 32, e00243. doi:10.1016/j.fooweb.2022.e00243

Briones-Fourzán P, Álvarez-Filip L, Barradas-Ortíz C, Morillo-Velarde PS, Negrete-Soto F, et al. (2019) Coral reef degradation differentially alters feeding ecology of co-occurring congeneric spiny lobsters. Frontiers in Marine Science 5, 516. doi:10.3389/fmars.2018.00516

Buckland A, Baker R, Loneragan N, Sheaves M (2017) Standardising fish stomach content analysis: the importance of prey condition. Fisheries Research 196, 126–140. doi:10.1016/j.fishres.2017.08.003

Castañeda I, Doherty TS, Fleming PA, Stobo-Wilson AM, Woinarski JCZ, Newsome TM (2022) Variation in red fox Vulpes vulpes diet in five continents. Mammal Review 52, 328–342. doi:10.1111/mam.12292

Charnov EL (1976) Optimal foraging: the marginal value theorem. Theoretical Population Biology 9, 129–136. doi:10.1016/0040-5809(76)90040-x

Chesson J (1978) Measuring preference in selective predation. Ecology 59, 211–215. doi:10.2307/1936364

Christensen V (1998) Fishery-induced changes in a marine ecosystem: insight from models of the Gulf of Thailand. Journal of Fish Biology 53, 128–142. doi:10.1111/j.1095-8649.1998.tb01023.x

Christensen V, Walters CJ (2004) Ecopath with Ecosim: methods, capabilities and limitations. Ecological Modelling 172, 109–139. doi:10.1016/j.ecolmodel.2003.09.003

Clements HS, Tambling CJ, Hayward MW, Kerley GIH (2014) An objective approach to determining the weight ranges of prey preferred by and accessible to the five large African carnivores. PLoS One 9, e101054. doi:10.1371/journal.pone.0101054

Dundas SJ, Hopkins AJM, Ruthrof KX, Tay NE, Burgess TI, et al. (2018) Digging mammals contribute to rhizosphere fungal community composition and seedling growth. Biodiversity and Conservation 27, 3071–3086. doi:10.1007/s10531-018-1575-1

Ellis JE, Wiens JA, Rodell CF, Anway JC (1976) A conceptual model of diet selection as an ecosystem process. Journal of Theoretical Biology 60, 93–108. doi:10.1016/0022-5193(76)90157-0

Fennessy ST, Pradervand P, de Bruyn PA (2010) Influence of the sardine run on selected nearshore predatory teleosts in Kwazulu-Natal. African Journal of Marine Science 32, 375–382. doi:10.2989/1814232x.2010.506988

Fischbein D, Corley JC (2022) Population ecology and classical biological control of forest insect pests in a changing world. Forest Ecology and Management 520, 120400. doi:10.1016/j.foreco.2022.120400

French B, Clarke KR, Platell ME, Potter IC (2013) An innovative statistical approach to constructing a readily comprehensible food