
I seek to better understand how abiotic and biotic factors cascade through food webs to shape communities and ecosystems, and the role of spatial scale on these processes. My research primarily focuses on food web theory, but also draws from other areas such as organismal physiology and biogeography, and utilizes a diverse suite of statistical and machine-learning tools to uncover biological mechanisms. I take advantage of the utility of arthropod food webs as realistic model systems, which I study along environmental gradients and in combination with field and laboratory experiments.
Disentangling Abiotic and Biotic Drivers of Species’ Distributions
A grand challenge in understanding the drivers of species distributions – and thus the makeup of ecological communities – is disentangling the relative importance of species’ physiological responses to abiotic conditions (e.g., climatic constraints and physical barriers to dispersal) vs. biotic interactions among species. I combined modeling techniques with observational surveys along environmental gradients to investigate the relative importance of abiotic and biotic processes in driving species distributions at both the geographical scale (Central and South America) and the scale of the landscape (the Monteverde region in Costa Rica). While traditional species distribution models (SDMs) only consider species bioclimatic niches (i.e., abiotic factors), my collaborators and I demonstrated how biotic mechanisms, as well as dispersal limits, can be successfully incorporated into SDMs, and showed that abiotic processes like climate and dispersal barriers are more important at driving the geographical distribution of a Neotropical damselfly than biotic processes (Amundrud et al. 2018, Freshwater Biology). At the smaller scale of the landscape, I demonstrated that the relative importance of abiotic and biotic drivers of insect distributions can be contingent on environmental conditions (Amundrud and Srivastava, in press: Global Ecology and Biogeography), emphasizing that the relative importance of biotic and abiotic drivers of species distributions can shift with climate change.

The Role of Species Interactions for Community and Ecosystem Responses to Global Change
As ecologists hasten to predict how communities and ecosystems respond to global change, most efforts still focus on direct responses of species to altered environmental conditions – ignoring complexities that arise from biotic processes. I study how indirect effects from altered species interactions mediate the ecological outcome of global change. By investigating the effects of overfishing and eutrophication on eelgrass mesograzer communities, I showed that indirect effects from predators on herbivore interactions play major roles in the trophic regulation of communities (Amundrud et al. 2015, Journal of Animal Ecology), shedding light on a potential mechanism of one of the fundamental questions in ecology: how species with similar resources coexist. By exploring the effects of climate change on bromeliad-dwelling insect communities, I demonstrated that disproportionately adverse effects of drought on keystone predators can reshape communities and alter ecosystem functions far beyond any changes resulting from direct effects of drought on individual species (Amundrud and Srivastava 2016, Ecology). In addition, I demonstrated how communities can be altered from species undergoing drought induced trophic niche shifts (Amundrud et al. 2016, Oecologia), highlighting the need to incorporate potential shifts in how species function under altered environmental conditions in climate change predictions. While this research demonstrates the importance of altered species interactions, there are additional aspects of multifaceted climate change that hamper our ability to make accurate predictions, such as multiple climatic variables shifting in concert, and uncertainty over the ability of species to develop in situ tolerance or track environmental change. I demonstrated how we can unravel some of these complexities, by performing controlled experiments that manipulated multiple climatic stressors, species interactions, and prior exposure of species to future climatic conditions, and thus showed how uncertainties arise from the interplay of multiple biotic and abiotic mechanisms of climate change (Amundrud and Srivastava 2019, Global Change Biology).

Mechanistic Underpinnings of Fundamental Ecological Patterns
One of the few general patterns in ecology is the near-universal increase in species richness with habitat size, but the mechanisms driving this pattern are still unclear. For my Masters thesis, I proposed that large habitats may be species rich because their environmental conditions are within the fundamental niche of more species. I tested this hypothesis using bromeliad-dwelling insect communities and found that, since the risk of drought decreases with bromeliad size, drought sensitivity predicts bromeliad size preferences (Amundrud and Srivastava 2015, Ecology). By demonstrating that physiological tolerance to environmental stress can be relevant in explaining why species richness increases with habitat size, this research sheds light on the mechanistic underpinnings of one of the most prominent patterns in ecology, and has far-reaching implications for biodiversity research given that environmental conditions are being altered in habitats around the world.