208 Manter Hall
My research seeks to understand the diversity of life. In order to understand diversity, we need to describe the ecological processes that determine how species can coexist together in communities, why certain species occur in some habitat types and not in others, and how diversity is generated in the first place. To answer these questions, my lab members and I conduct ecological field research in some of the most species-rich places on Earth, the rain forests of the Amazon and Borneo. We also have projects here in Nebraska, as well as in India.
I am community ecologist who primarily studies forests, although my research has also involved birds and primates. Community ecology is a subdiscipline of ecology that quantifies natural patterns in the distribution, abundance, and interactions between populations in space and time and seeks to explain the important processes generating those patterns.
Community ecology is at an exciting junction: new molecular, modeling, and computational tools allow us to answer questions about the diversity of life that have never before been possible to answer!
Although research interests in my laboratory group are broad, my primary foci have been on two dominant processes that interact in their effects on species diversity and distribution: the causes and consequences of the dispersal of seeds and the functional basis of demographic trade-offs as determinants of tree community assembly in Amazonian and Bornean rain forests.
I approach research by developing models that predict aspects of population and community dynamics from functions that incorporate mechanistic explanations of biological processes. I parameterize these models using large, long-term demographic data sets and quantitative natural history data on species' functional traits. I complement these models with manipulative experiments and information on species' evolutionary relationships to understand the contemporary and historical processes that determine the ecological patterns that we observe.
If you are interested in studying ecology as a graduate or undergraduate student in my lab, please contact me by email.
Below I describe in more detail three of my primary research projects.
Species distributions and niche specialization
A main research focus in the lab is testing hypotheses that explain how species can coexist together without one or a few highly competitive species dominating the community. One explanation is that species coexist by occupying slightly different ecological niches and hence trade-off performance in different habitats. But how are plant species sorted among habitats that they could conceivably occupy in the absence of interspecific competition?
To address this question, I have been working in a large forest dynamics plot in Borneo (Lambir Hills National Park in Malaysian Borneo) with collaborators from the Center for Tropical Forest Science, Harvard University, and Malaysia’s Forest Research Corporation. We have been examining possible demographic and functional mechanisms that may generate the striking soil-correlated tree species distributions observed at Lambir (Figure 1; Russo et al. 2005).
Figure 1. Distributions of five species of Shorea (Dipterocarpaceae) in the 52-ha CTFS-Asia plot in Borneo that specialize on sandy loam (A), loam (B), fine loam (C), or clay (D) soils or are generalists (no soil type specialization) (E). Circles are scaled according to the diameter of the tree, and lines represent elevation. Shading indicates soils on a gradient increasing in fertility and moisture: white, sandy loam; light green, loam; green, fine loam; and dark green, clay.
Our research has shown that these soil-correlated distributions can be explained in part by performance-based ecological sorting of species among soils. Sorting may be partly mediated by an interspecific demographic trade-off between a species' ability to tolerate low-resource conditions by having conservative demographic responses (slow growth and low mortality) vs. its ability to respond quickly to increases in resource availability (fast growth) (Russo et al. 2008). Mortality risk for species with intrinsically fast growth is greater on the poorest soil, which is consistent with the trade-off hypothesis.
This interspecific demographic trade-off can be seen as an emergent property resulting from functional constraints related to physiology, morphology, and resource allocation expressed at the individual level. I am developing models relating this demographic trade-off to the possible functional mechanisms underlying it, by measuring in situ variation in ecophysiological traits of several tree species and relating this variation to plant performance (e.g., Russo et al. 2010 AJB, Russo et al. 2010 Func. Ecol.).
Many hypotheses of plant species diversity involve seed dispersal because it shapes species’ distribution patterns at multiple spatial scales (Figures 2 & 3) and thereby has implicatoins for niche specialization. Seed dispersal, however, can oppose niche specialization, if dispersal is spatially extensive, or reinforce it, if dispersal is spatially clumped. I am interested in understanding which factors determine both large- (between-habitat) and small-scale (within-habitat) distributions of trees and what role contemporary ecological vs. historical evolutionary processes play in creating those distributions.
Figure 2. Plants produce seeds with a diversity of shapes, sizes, and colors. These variable seed traits may be important determinants of dispersal and early establishment.
Figure 3. Spatially aggregated seed dispersal may be important for patterns of tree species recruitment. Here are crowded seedlings and saplings of Shorea laxa, a gravity-dispersed tree, from two recruitment events in Bornean rain forest.
To address these questions, I have been using comparative phylogenetic analyses of ecological and evolutionary covariation in seed dispersal mode, seed size, and niche specialization of tree species. With collaborators at the University of Miami and the Center for Tropical Forest Science, I am evaluating whether evolutionary divergences in dispersal mode and seed size of tree species are associated with divergences in their ecological niches and whether interspecific variation in tree species’ small-scale distribution could be explained by these three traits (Russo et al. 2007).
I have also been examining the role of seed dispersal in determining species distribution in a neotropical nutmeg tree, Virola calophylla (Myristicaceae) in the Peruvian Amazon. Along with collaborators at the University of Illinois, I have developed a mechanistic model of seed dispersal that predicts the spatial distribution pattern of V. calophylla seeds at the forest-stand scale, based on the behavior and movement patterns of its most important dispersal agent, the spider monkey (Ateles paniscus) (Russo et al. 2006).
Our results suggest that the clumped seed dispersal patterns often generated by vertebrate dispersers, such as the spider monkey (Russo & Augspurger 2004), can influence the spatial structuring of some tropical tree populations more so than even strong density-dependent mortality. Understanding how dispersers affect the demography of tropical trees is vitally important, given global losses of vertebrate dispersers from forests due to poaching.
My lab will continue to study the ecological and evolutionary consequences of seed dispersal at multiple spatial and temporal scales. Future research will use our mechanistic model of seed dispersal, demographic models, and population genetic approaches to estimate gene flow by seed dispersal and how it influences the spatial structure of demographic and population genetic variation at different life stages and at different spatial scales.
Competition along environmental gradients
Competitive dynamics between tree species is an important factor determining forest diversity. The outcome of competition, however, varies depending on the availability of resources in the environment and the competitors’ ecological strategies. I originally began testing models of competition in forests along environmental gradients in New Zealand with collaborators at the University of Cambridge, U.K., Landcare Research, New Zealand, and Columbia University. New Zealand is classically considered a cradle of ancient diversity because its forests contain species from relatively old lineages with Gondwanan distributions, such as the conifer family Podocarpaceae. Not only are podocarps now largely restricted to South-temperate forests, but where they do occur, it is often on low-fertility soils. One hypothesis to explain their restricted distribution is that they are inferior competitors to angiosperms, such as beeches in the genus Nothofagus, which have come to dominate much of New Zealand’s forests. We are parameterizing neighborhood models of tree species competition and quantify the extent to which Angiosperms may exclude podocarps from preferred, nutrient-rich habitats in New Zealand. We are also examining how individual performance varies along climatic (temperature) ranges to predict potential range shifts that may accompany future climate change.
Members of the Russo lab are also developing neighborhood competition models in Borneo to investigate whether competitive dynamics shift along soil resource gradients. Thus far, our modeling work shows that tree height growth rates are faster on more nutrient-rich, moist soil, where understory light levels are lower (Russo et al., in press), suggesting that competition for light is more intense here compared to the less fertile, drier soil type (Heineman et al. 2011).
Russo, S.E., R. Legge, K. Weber, E. Brodie, K.C. Goldfarb, A. Benson, and S. Tan. 2012. Bacterial community structure of contrasting soils underlying Bornean rain forests: inferences from microarray and next-generation sequencing methods. Soil Biology and Biochemistry, In press.
Russo, S.E.,L. Zhang, and S. Tan. 2012. Covariation between understorey light environments and soil resources in Bornean mixed dipterocarp rain forest. Journal of Tropical Ecology 28:33–44.
Heineman, K., E. Jensen, B. Bogenrief, A. Shapland, S. Tan, R. Rebarber, S.E. Russo. 2011. The effect of belowground resources on aboveground growth and allometry in six Bornean tree species. Forest Ecology and Management 261:1820-1832.
Russo, S.E., W.L. Cannon, C. Elowsky, S. Tan, S.J. Davies. 2010. Variation in leaf stomatal traits of 28 tree species in relation to water-use efficiency along an edaphic gradient in Bornean rain forest. American Journal of Botany 97: 1109–1120.
Russo, S.E., K. Jenkins, S. Wiser, D.A. Coomes. 2010. Relationships between wood traits and growth and mortality rates of New Zealand tree species. Functional Ecology 24: 253–262.
Russo, S.E., P. Brown, S. Tan, S.J. Davies. 2008. Interspecific demographic trade-offs and soil-related habitat associations of tree species along resource gradients. Journal of Ecology 96:192–203.
Russo, S.E, S.K. Wiser, and D.A. Coomes. 2007. Growth-size scaling relationships of woody plant species differ from productions of the metabolic Ecology Model. Ecology letters, 10: 889–901
Russo, S.E., Potts, M.D., Davies, S.J. & S.Tan. 2007. Determinants of tree species distributions: Comparing the roles of dispersal, seed size, and soil specialization in a Bornean rain forest. In: Seed Dispersal: Theory and its Application in a Changing World (eds. Dennis, A., Schupp, E.W., Green, R. & Wescott, D.). CAB International, New York.
Russo, S.E.,S. Portnoy, C.K. Augspurger. 2006. Incorporating animal behavior into seed dispersal models: Implications for seed shadows and an example for a primate-dispersed tree. Ecology 87:3160-3174.
Chapman, C.A. and S.E. Russo. 2006. Primate seed dispersal: Linking behavioral ecology with forest community structure. In Primates in Perspective (eds. C.J. Campbell, A.F. Fuentes, K.C. MacKinnon, M. Panger, and S. Bearder). Oxford University Press.
Condit, R., P. Ashton, S. Bunyavejchewin, H. S. Dattaraja, S. Davies, S. Esufali, C. Ewango, R. Foster, I. A. U. N. Gunatilleke, C. V. S. Gunatilleke, P. Hall, K. E. Harms, T. Hart, C. Hernandez, S. Hubbell, A. Itoh, S. Kiratiprayoon, J. LaFrankie, S. L. d. Lao, J. Makana, M. N. S. Noor, A. R. Kassim, S. Russo, R. Sukumar, C. Samper, H. S. Suresh, S. Tan, S. Thomas, R. Valencia, M. Vallejo, G. Villa, and T. Zillio. 2006. Importance of demographic niches to tree diversity. Science 313:98-101.
Russo, S. E., S. J. Davies, D. A. King, and S. Tan. 2005. Soil-related performance variation and distributions of tree species in a Bornean rain forest. Journal of Ecology 93:879-889.
Russo, S., C. Campbell, J. Dew, P. Stevenson, and S. Suarez. 2005. A multi-forest comparison of dietary preferences and seed dispersal by Ateles spp. International Journal of Primatology 26:1017-1037.
Russo, S. E. 2005. Linking seed fate to dispersal patterns: identifying factors affecting predation and scatter-hoarding of seeds of Virola calophylla in Peru. Journal of Tropical Ecology 21:243-253.
Russo, S. E., and C. K. Augspurger. 2004. Aggregated seed dispersal by spider monkeys limits recruitment to clumped patterns in Virola calophylla. Ecology Letters 7:1058-1067.
Russo, S. E. 2003. Responses of dispersal agents to tree and fruit traits in Virola calophylla (Myristicaceae): Implications for selection. Oecologia 136:80-87.
Russo, S. E., S. K. Robinson, and J. Terborgh. 2003. Size-abundance relationships in an Amazonian bird community: Implications for the energetic equivalence rule. The American Naturalist 161:267-283.