|STEPHEN B. HEARD B.Sc. (Waterloo), Ph.D. (Pennsylvania).
Evolutionary and community ecology; ecological controls on biodiversity.
My research interests are broad, but are centred on ecological controls on the evolution of biodiversity. My students and I seek to understand how ecological interactions and ecological circumstances have influenced patterns in speciation and extinction rates among lineages - and therefore have shaped the modern diversity of life. Why, for instance, might beetles have diversified so much, but penguins so little? How can we test ideas about ecological controls on speciation rates when we can't observe the past directly? We are currently taking two major approaches to questions like these.
First, we are studying the evolutionary ecology of insect herbivores of goldenrods (and of their parasitoids). We are particularly interested in the ecology and evolution of diet specialization, including the evolution of host-specialist races, because host-race formation and sympatric speciation may play an important role in generating the astounding diversity of phytophagous insects. We have demonstrated repeated, parallel evolution of specialist host-race pairs in several gallmaking insects associated with the goldenrods Solidago altissima and S. gigantea, and we have also found that differentiation beginning with herbivores can cascade to drive differentiation of parasitoids too. In a new twist to this project, we are now assessing the impact of host-specialist and host-generalist herbivores on the endangered Saint Laurence Aster (Symphiotrichum laurentianum), an annual that appears to be under substantial population pressure from insect herbivores.
Second, we are examining patterns in the shapes of evolutionary trees (phylogenies), both real and computer-simulated, with an eye to understanding how features of individual and population ecology shape macroevolutionary patterns like among-lineage variation in speciation rates. For instance, we have used tree shape to test for ancestor-descendent heritability of diversification rates; we have asked whether tree shape can reveal patterns of ecological selectivity in past mass extinctions; and we continue to seek connections between plausible models of macroevolution and patterns of diversity among modern-day lineages. This work has led us most recently to examining the phylogenetic structure of biodiversity in worldwide clades, regional faunas, and local (community) assemblages.
Other recent projects include:
- studies of interspecific interactions among benthic stream invertebrates; and
- studies of geographic pattern in allocation to anti-herbivore defenses in milkweeds
Some Recent Publications:
Heard, S.B. and E.K. Kitts. 2012. Impact of attack by Gnorimoschema gallmakers on their ancestral and novel Solidago hosts. Evolutionary Ecology 26:879-892 (pdf)
Woods, E.C., A.P. Hastings, N.E. Turley, S.B. Heard, and A.A. Agrawal. 2012. Adaptive geographical clines in the growth and defense of a native plant. Ecological Monographs 82:149-168 (pdf).
Heard, S.B. 2012. Use of host-plant trait space by phytophagous insects during host-associated differentiation: the gape-and-pinch model. International Journal of Ecology 2012:ID192345 (pdf).
Ancheta, J. and Heard, S.B. 2011. Impacts of insect herbivores on rare plant populations. Biological Conservation 144:2395-2402 (pdf).
Ancheta, J., S.B. Heard, and J.W. Lyons. 2010. Impacts of salinity and simulated herbivory on survival and reproduction of the threatened Gulf of St. Lawrence Aster, Symphyotrichum laurentianum. Botany 88: 737-744 (pdf).
Vamosi, S.M., S.B. Heard, J.C. Vamosi, and C.O. Webb. 2009. Emerging patterns in the comparative analysis of phylogenetic community structure. Molecular Ecology 18:572-592 (pdf).
Heard, S.B. and L.C. Remer. 2008. Travel costs, oviposition behaviour,and the dynamics of insect-plant systems. Theoretical Ecology 1:179-188 (pdf).
Halverson, K., S.B. Heard, J.D. Nason, and J.O. Stireman III. 2008. Origins, distribution and local co-occurrence of polyploid cytotypes in Solidago altissima (Asteraceae). American Journal of Botany 95:50-58 (pdf).
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Last Update: 11 April 2013
This document: http://www.unb.ca/departs/science/biology/Faculty/Heard.html