Assistant Professor, Biology
PhD, Univ of Tennessee, Knoxville, Ecology & Evol Biology (2003)
Ecological and evolutionary community assembly
I study how ecological communities assemble, with emphasis on historical contingency in community structure, ecosystem functioning, biological invasion and ecological restoration, using various methods (experimental, theoretical and comparative) and organisms (bacteria, protists, fungi, plants and animals) in collaboration with interdisciplinary colleagues.
Community structure often shows non-random relationships with the size, productivity, connectivity and other characteristics of localities. Using computer simulations and microbial experiments, I have found that these relationships depend on the history of community assembly, or the sequence and timing in which species join communities, at multiple spatial scales.
Recently, I am studying how historically derived variation in community structure affects the way ecosystems function. My current focus for this work is wood-decay fungi and their consumers. With New Zealand researchers, I am doing experiments to ask how assembly history interacts with top-down and bottom-up forces to alter fungal communities that drive nutrient cycling in ecosystems.
I am also interested in incorporating evolutionary diversification in community assembly theory, which has focused mainly on ecological, as opposed to evolutionary, dynamics. Our microbial experiments so far have shown that immigration history influences the extent of evolutionary diversification via ecological mechanisms such as competitive neutrality and indirect facilitation.
Although much of my work involves laboratory and theoretical methods, I maintain the same level of interest in conducting field research that addresses both fundamental questions and environmental issues such as biological invasion and ecological restoration. For example, I have been involved in a project on rat-induced community changes on New Zealand islands. Building on this effort, I am now working with collaborators to develop a project that will use numerous forest fragments created by lava flow in Hawaii. With this system, we seek to understand how the response of native plant and animal communities to non-native mammals varies with ecosystem size and landscape context.
Diversity in biological communities is a historical product of immigration, diversification and extinction, but the combined effect of these processes is poorly understood. Here we show that the order and timing of immigration controls the extent of diversification. When an ancestral bacterial genotype was introduced into a spatially structured habitat, it rapidly diversified into multiple niche-specialist types. However, diversification was suppressed when a niche-specialist type was introduced before, or shortly after, introduction of the ancestral genotype. In contrast, little suppression occurred when the same niche specialist was introduced relatively late. The negative impact of early arriving immigrants was attributable to the historically sensitive outcome of interactions involving neutral competition and indirect facilitation. Ultimately, the entire boom-and-bust dynamics of adaptive radiation were altered. These results demonstrate that immigration and diversification are tightly linked processes, with small differences in immigration history greatly affecting the evolutionary emergence of diversity.
View details for DOI 10.1038/nature05629
View details for Web of Science ID 000245079500039
View details for PubMedID 17377582
Many ecological dynamics occur over time-scales that are well beyond the duration of conventional experiments or observations. One useful approach to overcome this problem is extrapolation of temporal dynamics from spatial variation. We review two complementary variants of this approach that have been of late increasingly employed: the use of natural gradients to infer anthropogenic effects and the use of anthropogenic gradients to infer natural dynamics. Recent studies have considered a variety of naturally occurring gradients associated with climate, CO2, disturbance and biodiversity gradients, as well as anthropogenic gradients such as those created by biological invasions, habitat fragmentation and land abandonment. These studies show that natural gradients are useful in predicting long-term consequences of human-induced environmental changes, whereas anthropogenic gradients are helpful in inferring the mechanisms behind natural dynamics because covarying factors are often more clearly understood in anthropogenic gradients than in natural gradients. We classify these studies into several categories, each with different strengths and weaknesses, and outline how the limitations can be overcome by combining the gradient-based approach with other approaches. Overall, studies reviewed here demonstrate that the development of basic ecological concepts and the application of these concepts to environmental problems can be more effective when conducted complementarily than when pursued separately.
View details for DOI 10.1098/rspb.2005.3277
View details for Web of Science ID 000232634600001
View details for PubMedID 16191623
Identification of the causes of productivity-species diversity relationships remains a central topic of ecological research. Different relations have been attributed to the influence of disturbance, consumers, niche specialization and spatial scale. One unexplored cause is the history of community assembly, the partly stochastic sequential arrival of species from a regional pool of potential community members. The sequence of species arrival can greatly affect community structure. If assembly sequence interacts with productivity to influence diversity, different sequences can contribute to variation in productivity-diversity relationships. Here we report a test of this hypothesis by assembling aquatic microbial communities at five productivity levels using four assembly sequences. About 30 generations after assembly, productivity-diversity relationships took various forms, including a positive, a hump-shaped, a U-shaped and a non-significant pattern, depending on assembly sequence. This variation resulted from idiosyncratic joint effects of assembly sequence, productivity and species identity on species abundances. We suggest that the history of community assembly should be added to the growing list of factors that influence productivity-biodiversity patterns.
View details for DOI 10.1038/nature01785
View details for Web of Science ID 000184318400042
View details for PubMedID 12879069