Changing species interaction networks

cheetahs_impalaNetworks are everywhere, and our ability to understand how they respond to change and to control them is critical for everything from developing medical therapies to managing endangered pollinators. My work focuses on the processes that govern the response of ecological communities to altered species interaction networks, and how these processes shape novel ecological communities. This works addresses the grand predictive challenge for ecology in an era of global environmental change, to predict how the development of novel interactions, alteration of existing interactions, and the extinction of interactions influence broad patterns in biodiversity and evolutionary change.

Global change drivers, by causing profound impacts on species’ abiotic and biotic environments, threaten the capacity of ecosystems to sustain biological diversity and ecosystem functions that are important for people. My research works to understand how global change drivers affect ecological networks—and in turn how to conserve and manage these networks—by synthesizing empirical data and advancing theory in evolutionary ecology to explain variation among species in their responses to altered species interactions. Theory on species coexistence is critical for making these links because it explains why species vary in their ecological roles and how traits of species reflect these differences. Knowledge of the links between these traits and the strategies most affected by global change can help predict the winners and losers under anthropogenic change.

I am pursuing these interests with research on the consequences of defaunation following the introduction of the invasive brown treesnake on Guam with Haldre Rogers, with field projects identifying the plant traits that mediate interactions with antagonists in Panama, and with synthesis of global mutualistic interaction and trait databases to understand the species most vulnerable to mutualism disruption. This work has implications for range dynamics in the context of climate change, persistence of animal-dispersed tree species important for tropical forest carbon storage, and regeneration of deforested areas and secondary forest.


The seed dispersal mutualism

PrintMutualistic interactions between plants and their seed dispersers generate and sustain
plant diversity, and mutualisms provide compelling systems to understand the evolution of nature’s impressive diversity of plant and animal traits. My research in this area has focused on the breadth of mechanisms by which frugivores benefit plants, the ecological contexts where these benefits occur, and variation among species in the magnitude of these benefits. These projects have focused on detailed studies of wild chilies with Josh Tewksbury and Doug Levey and community-scale studies of dispersal benefits in the Mariana Islands working with Haldre Rogers. In particular, I am interested in the reasons why species vary in their demographic dependence on seed dispersal and how diversifying processes cause differentiation in mutualistic strategies among species.

Mutualistic network approaches offer useful tools for understanding the dynamics of mutualistic communities. The promise of this approach is its capacity to use simple interaction data to understand the assembly and disassembly of mutualistic communities. My ongoing work suggests that including other axes of variation among species—in addition to interaction frequency data—can reorient our understanding of the stability of mutualistic networks and their responses to change.


Maintenance of species and trait diversity

IMG_1699Understanding the processes that allow species to coexist is a central goal of ecology, and species interactions are at the core of the diversity-maintaining processes that shape ecological communities. A key coexistence mechanism caused by interactions between plants and their predators and pathogens is conspecific negative density dependence. My research has addressed the role of conspecific density dependence in tropical forest dynamics, working to identify the agents that cause this phenomenon and to assess how variation in the strength of density dependence influences species abundance and diversity.

My research also focuses on the causes and consequences of variation in traits among and within species. Recent interest among ecologists has focused on links between functional traits and coexistence, particularly with coexistence mechanisms involving competitive interactions among plants. Extending these concepts to interactions with mutualists and antagonists, my ongoing projects assess how physical and chemical defense traits influence interactions with antagonists, how traits of mutualists determine the diversity and identity of their partners, and how tradeoffs operating within species underlie intraspecific trait variation. These projects point toward a broader importance of traits for plant coexistence: traits mediate differentiation among plant species in their interactions with the abiotic environment, competitors, natural enemies, and mutualists. My major collaborators on these projects include Joe Wright and Sofia Gripenberg for work on Barro Colorado Island and Haldre Rogers in the Mariana Islands.


This work supported by: