Anushika Herath: Animal personality drives individual dietary specialisation across multiple dimensions in a mammalian herbivore

In this new post, Anushika. P.H.M. Herath, a post-doctoral research associate from The University of Sydney presents her work on the influence of animal personality of individual diet specialisation and the describes her experience working with Australian native fauna.

Anushika with her daughter in Ku-ring-gai Chase National Park, NSW, Australia
Anushika with her daughter in Ku-ring-gai Chase National Park, NSW, Australia

About the paper

Within a species, individuals vary in numerous traits including their sex, personality, and physiology. These traits affect how individuals interact with the environment around them including what they eat, where they go and the risks they face from predators, with important ecological and evolutionary implications. In our paper in functional ecology, we focus on testing the link between two important facets of individual trait variation: Individual dietary specialisation (i.e. consistent individual variation in diet) and animal personality (i.e. consistent individual variation in behaviour). Much is known about animal personality and — separately — individual dietary specialisation in a variety of taxa. But, whether animal personality can explain the variation in dietary niche among individuals of the same population or species is, until now, unknown. Our paper addresses this knowledge gap by demonstrating an important association between animal personality and individual dietary specialisation in multiple dimensions. To do this, we used free-ranging common brushtail possums (Trichosurus vulpecula), a dietary generalist herbivore at the species level, in an urban-native habitat context.

What is the background behind your paper?

Anushika holding a possum in a hessian bag during her field work in Ku-ring-gai Chase National Park
Anushika holding a possum in a hessian bag during her field work in Ku-ring-gai Chase National Park

This research addresses a broader question of how animal personality influences variation in ecologically important features such as diet, foraging behaviour, parasitic load and gut microbiome among individuals of the same population. This study was part of a larger effort to investigate influence of animal personality on such important ecological traits. For example our previous work shows that animal personality influences space use and the problem solving ability of common brushtail possums.

What are the key messages of your article?

Our article demonstrates animal personality as a major driver of individual realised diet and dietary specialisation in multiple dimensions. Proactive possums (more exploratory, more active and bold) had a broad and high quality diet. In contrast, reactive possums (less exploratory, less active and shy) ate a narrow and low quality diet. This personality-mediated dietary specialisation has a range of significant applied and fundamental implications that we discuss in the paper in detail.

How is your paper new or different from other work in this area?

There is a vast array of literature on how animal personality influences individual trait variation and responses to the environment including space use, exposure to parasites as well as how animals react to the dual costs of food and fear. Similarly, many studies have focused on extrinsic drivers of individual specialisation including inter and intra competition, predation and ecological opportunity. Our paper is unique because it is the first empirical study to show animal personality as an important intrinsic driver of diet and dietary specialisation among individuals within the same species. By uniting animal personality and individual specialisation, our work helps fill a major knowledge gap in individual variation studies and helps us understand the implications of personality and diet syndromes.

About the research

What is the broader impact of your paper (outside of your specific species/study system?)

We discuss the ecological implications of personality-driven individual dietary specialisation beyond our study species. Fundamentally, personality-mediated individual dietary specialisation can lead to niche partitioning, which in turn, we predict leads to greater coexistence of individuals within a population, less intraspecific competition and higher carrying capacities of populations.

Why is it important?

Demonstrating and understanding personality-driven individual dietary specialisation provides an important basis for improving biodiversity conservation and pest management. Our findings are relevant to the management of both threatened and invasive species, by identifying behavioural-dietary phenotypes that will disproportionately affect different ecological interactions such as food web dynamics. For example, proactive–generalist possums are likely to be super pests that cause damage to pastures, crops, vegetables and home garden species due to their high tendency to eat for high-quality foods found on the ground  . Our results also highlight the importance of catering for diverse dietary motivations of individuals, as a function of personality, for conservation programs to succeed.

Did you have any problems setting up the experiment/gathering your data?

Anushika releasing a possum after conducting behavioural tests at 2.30 am in Ku-ring-gai Chase National Park.
Anushika releasing a possum after conducting behavioural tests at 2.30 am in Ku-ring-gai Chase National Park.

The biggest hurdle I faced during this research was to capture enough possums to obtain both behavioural and diet data. Brushtail possums are nocturnal solitary mammals, so studying possums means that you have to work at night in a national park. We set traps in the late afternoon just before the sunset and began to conduct behavioural tests from midnight, giving possums enough time to actively forage. It was hard to trap and conduct behavioural tests at night; it was even harder to capture the same possums every season to get repeat measures of diet and behaviour (roughly 50% of the possums were caught only once). It took more than two years and countless sleepless nights to get a sample size to satisfy reviewers, even with a few of us working together!

Were you surprised by anything when working on it?

During this study, I spent many hours collecting and studying leaf material from more than 100 plant species to determine diet of possums. I was amazed to see how different and unique each plant species was, not only in observable features such as leaf shape and size but in microscopic level features (epidermal cell arrangement) and in genetic level (difference in DNA sequences) features. Looking at a possum scat sample though a microscope felt like as if I was looking at the forest patches possums were foraging – just at the microscopic level.

What are the big questions still to answer?

We still don’t know whether the different diet-personality phenotypes we observed also have different physiological capacity to confront plant defences (digestive physiology) and predation risk (stress physiology). Answering this question will bring together the suite of characteristics that may together help us understand how and why animals have different ways of solving the fundamental problem of living in a varied world.

What is the next step in this field going to be?

Now what we know there is an association between animal personality and their diet differences, we can test whether these behavioural-diet syndromes affect other individual variation traits: for example, variation in pathogenic disease occurrence in urban-adapted animals, or how behavioural-diet syndromes are associated with variation in gut microbiome

What would you like to do next?

I’m currently working on a project that tests the links between host individual trait variation and parasitic diseases that human and animals share. My work aims to find the links between individual variation of gut parasite infections and individual host heterogeneities including animal personality, diet, gut microbiome and physiology using common brushtail possum hosts. This project is looking at reverse zoonoses: diseases that our wildlife may be picking up from humans and transferring — as another form of anthropogenic pollution — from cities to natural ecosystems.

About the author

How did you get involved in ecology?

Anushika extracting DNA from common brushtail possum faecal samples
Anushika extracting DNA from common brushtail possum faecal samples

Even since I was a little girl I was intrigued by the natural world. Growing up in a Sri Lanka, which is a tropical island and a biodiversity hotspot, helped me to embrace and appreciate nature. In Sri Lanka I completed my honours degree and my master’s degree in ecology, where I had the opportunity to conduct research on herbivore behaviour and medical parasitology. During my honours research I studied the diversity and distribution of medicinal plants in Mihinthale, a wildlife sanctuary in Sri Lanka, from which I gained an in-depth knowledge on how to identify plant species. My passion to study unique Australian ecosystems and marsupials lead me to move to Australia where I completed my PhD at the University of Sydney. During my candidature, I explored the links between personality, individual dietary specialisation and parasite occurrence in common brushtail possums. I was very lucky to be a part of two wonderful research lab groups, the McArthur Behavioural Ecology Lab led by Prof. Clare McArthur, and the Behavioural Ecology and Conservation Lab lead by Prof. Peter Banks. Working with such experts in my field and gaining experience has been one of the highlights of my PhD career.

At present I work as a postdoctoral research associate in the School of Life and Environmental Science, at the The University of Sydney. I’m currently, working on a Discovery Project funded by the Australian Research Council, which explores how individual trait variation including animal personality, space use, and gut microbiome, sex, and diet are associated with parasitic infections that humans and urban-adapted wildlife share.

What project/article are you most proud of?

I’m most proud of the project that I am currently working on. This project links both my experience in the field of medical parasitology and ecology as well as addressing a pressing issue how disease spreads between humans and wildlife. This project will help to enhance our understanding of whether, and how, variation in traits among individuals within a population may influence pathogenic disease spread between humans and animals.

What is the best thing about being an ecologist?

You get to spend time in nature and answer important questions and also as an ecologist, you can play an active role in conserving nature.

What is the worst thing about being an ecologist?

I can’t think of anything bad, but more funds for ecological research would be good.

What do you do in your spare time?

My love for nature as well as my family is deep rooted in me. So I spend most of my spare time going on bush walks  in national parks with my family. I love taking pictures of wildlife during these walks.

One piece of advice for someone in your field

A misconception about becoming a scientist is that you miss out on your normal life. For those who think is it hard to balance every facet of your life while focusing on your research, my advice is that, “yes you can”. While following my dream of becoming an ecologist, I migrated from Sri Lanka to Australia, and lead a happy married life raising a lovely daughter and taking care of my father before he passed away due to cancer. So don’t be afraid to leave your comfort zone and follow your dreams, because the world needs ecologists now more than ever.

Read the article in full here.

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