Biological Invasions
Biological invasions have dramatically altered the natural world and continue to do so, threatening native species and communities and affecting human well being. At the same time, they offer unique opportunities to probe questions such as the nature of range limits and the speed of evolutionary change on unprecedented spatial and temporal scales. I have worked on both experimental and conceptual approaches to better understanding biological invasions, particularly in plant communities. Current work (with Norma Fowler and Catherine Graham) concerns studying the demography of the incipient invasion of Centaurea stoebe in the eastern U.S. at a range of spatial scales, across a large number of populations. We predicted that the growth of different populations would vary greatly at landscape levels, and preliminary results seem to be confirming those predictions. We are also investigating the environmental factors associated most closely with rapid population growth.
Experimental work in the past (with Manuel Lerdau and others) included field manipulations in which species introductions and manipulation of environmental variables (light and soil resources) tested which factors are most important in facilitating or hindering invasion. The work has already confirmed some suspected relationships and presented a number of surprises. Invasion is positively associated with native species diversity, and with soil nitrogen and calcium. Poor soil resources (but not light or disturbance) exclude invasive species from pine barrens communities, but light availability combined with soil resources are critical in allowing or blocking invasives in mixed hardwood forests. We also examined the ties between the community effects of invasion and the effects at the ecosystem level by evaluating plant nutrient uptake, storage and recycling in leaf litter.
Conceptual and theoretical work on invasions has concerned several different approaches and questions. In some highly controversial work, Dr. Dianna Padilla and I examined the evidence for the effects of invasive species in causing the decline of native species at continental and global scales, and found that the story was more complex than many had believed, and that the evidence in some cases for claims that invasive species are one of the major causes of native declines and extinctions is very limited. Other work, with Drs. Gordon Fox, Glenda Wardle, Inderjit and Daniel (Max) Taub, has attempted to integrate the many hypotheses and theories attempting to explain biological invasions. Invasion biology is clearly ripe for conceptual synthesis and integration. Rapid advances in understanding and managing biological invasions depend upon developing a broadly applicable conceptual framework for a discipline that has until recently focused largely on case studies and single factor hypotheses to explain invasions. As in the experimental work on invasions, a central issue is the need to consider multiple causal factors and interactions among hypothesized causal factors. Novel insights that emerge from our synthesis include a new look at the importance of lags at each stage of invasion, rather than just at the initial stages, and an emphasis on how explicit consideration of demographic processes will facilitate quantitative and testable evaluation of causal factors.
Experimental work in the past (with Manuel Lerdau and others) included field manipulations in which species introductions and manipulation of environmental variables (light and soil resources) tested which factors are most important in facilitating or hindering invasion. The work has already confirmed some suspected relationships and presented a number of surprises. Invasion is positively associated with native species diversity, and with soil nitrogen and calcium. Poor soil resources (but not light or disturbance) exclude invasive species from pine barrens communities, but light availability combined with soil resources are critical in allowing or blocking invasives in mixed hardwood forests. We also examined the ties between the community effects of invasion and the effects at the ecosystem level by evaluating plant nutrient uptake, storage and recycling in leaf litter.
Conceptual and theoretical work on invasions has concerned several different approaches and questions. In some highly controversial work, Dr. Dianna Padilla and I examined the evidence for the effects of invasive species in causing the decline of native species at continental and global scales, and found that the story was more complex than many had believed, and that the evidence in some cases for claims that invasive species are one of the major causes of native declines and extinctions is very limited. Other work, with Drs. Gordon Fox, Glenda Wardle, Inderjit and Daniel (Max) Taub, has attempted to integrate the many hypotheses and theories attempting to explain biological invasions. Invasion biology is clearly ripe for conceptual synthesis and integration. Rapid advances in understanding and managing biological invasions depend upon developing a broadly applicable conceptual framework for a discipline that has until recently focused largely on case studies and single factor hypotheses to explain invasions. As in the experimental work on invasions, a central issue is the need to consider multiple causal factors and interactions among hypothesized causal factors. Novel insights that emerge from our synthesis include a new look at the importance of lags at each stage of invasion, rather than just at the initial stages, and an emphasis on how explicit consideration of demographic processes will facilitate quantitative and testable evaluation of causal factors.
Research Synthesis, Meta-analysis and Systematic Reviews
My early work in meta-analysis in ecology made contemporary quantitative research synthesis and meta-analysis better known and accessible in the fields of ecology and evolution, changing the way we conceptualize and review scientific data in these fields. In addition to scientific publications on methodology and application of research synthesis in these areas, I have collaborated on software to make these techniques easier to implement with ecological questions and ecological data (MetaWin and OpenMEE software). This work has been controversial and highly influential, and grew out of my interests in applying rigorous statistical methodology to the analysis of ecological data and the design of ecological experiments. I have offered meta-analysis workshops across the U.S. and in many different countries. I am a co-editor of the Handbook of Meta-analysis in Ecology and Evolution (Koricheva, Gurevitch and Mengersen 2013).
OpenMEE software is free, open access--you can download the program by clicking on the link.
OpenMEE software is free, open access--you can download the program by clicking on the link.
