Environmental variation

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The environment experienced by individual organisms varies on multiple spatial and temporal scales, resulting in complex effects on population ecology and evolution. Such environmental variation can be anthropogenic in origin, through climate change, land management decisions, or species introductions, for example. Alternatively, variation may result from "natural" processes, or a combination of natural and anthropogenic causes. The net result is variation in habitat quality across space and/or time, including differences in abiotic factors such as rainfall and temperature, and differences in biotic factors such as prey, predators, competitors and parasites.

The ecological and evolutionary effects of habitat variation will depend on how individual organisms and populations respond to that variation. The degree to which fitness is buffered against variation or to which variation can be exploited to increase fitness will influence effects that humans have on local populations and hence biodiversity as a whole.

The spatial and/or temporal scale over which variation occurs is also an important determinant of the ecological and evolutionary effects of habitat. Large- and small-scale effects may be associated with different probabilities of population persistence. Understanding these effects will facilitate development of conservation priorities and triage of resource expenditure on conservation issues.

Center research addresses these issues with a mixture of long- and short-term studies aimed at both ecological and evolutionary questions using a variety of species. 

• For example, Carol Boggs is using several different butterfly species to ask how variation in the nutritional environment affects life history traits of reproduction, survival and foraging, and how those then combine to affect individual fitness and population dynamics.  Boggs uses a combination of modeling and empirical field and lab studies to address this issue. 
  
  
• In a separate study, Boggs is exploring the role of climate variation as a driver of the population dynamics of an introduced butterfly in Colorad o , Euphydryas gillettii.  This analysis will aid our understanding of the effects on populations of on-going and future changes in variance in climate parameters, not just changes in the mean.
  
  
• Boggs' work parallels CCB’s long-term study of Euphydryas editha bayensis, the bay checkerspot butterfly, led by Paul Ehrlich and a series of collaborators. We understand a great deal about the role of environmental variation in determining the population dynamics of the sub-species. Future work may include further analyses of the effects of spatial habitat heterogeneity in the remaining large population in the East Bay hills, including factors determining the distribution of the population through time and across space, and effects of habitat heterogeneity on genetic structure of the population.
  
  
• Erica Fleishman, John Fay, Ralph Mac Nally and collaborators are examining whether environmental variables including vegetation, topography, and climate can explain and predict species richness and the distributions of individual species of birds and butterflies. Their research typically incorporates field data, spatial analysis, and Bayesian modeling approaches. This work allows managers to anticipate the effect of different environmental changes and land-use policies on ecological communities.
  
  
• With colleagues at the Rocky Mountain Research Station, High Desert Ecological Research Institute, Colorado State University, and other institutions, Fleishman also is examining the response of wildlife and vegetation to prescribed fire and wildfire in pinyon-juniper and riparian woodlands in the Great Basin. Documentation and interpretation of the effects of fuel reduction treatments on natural resources plays an important role in evaluating the costs and benefits of management alternatives in ecological and financial terms. As one component of this work, remote sensing is being integrated with field research to examine changes in the distribution of birds and bird habitats during the past 20–25 years. Observed changes will provide a benchmark against which the effects of future management actions can be measured.

Participants

• Carol Boggs
• Jeanne Chambers
• Brett Dickson
• David Dobkin
• Paul Ehrlich
• John Fay
• Erica Fleishman
• Jessica Hellmann
• Ralph Mac Nally
• Barry Noon
• Diane O’Brien
• Karen Seto
• Jim Thomson

Publications

Boggs, C. L., and D. D. Murphy. 1997. Community composition in mountain ecosystems: climatic determinants of montane butterfly distributions. Global Ecology & Biogeography Letters 6: 39-48.

Boggs, C. L. 1997. Resource allocation in variable environments: Comparing insects and plants. Pages 73-92 in F. Bazzaz and J. Grace, eds. Plant Resource Allocation. Academic Press.

—. 1997. Reproductive allocation from reserves and income in butterfly species with differing adult diets. Ecology 78: 181-191.

Boggs, C. L., W. B. Watt, and P. R. Ehrlich, eds. 2003. Butterflies: Evolution and Ecology Taking Flight. University of Chicago Press.

Boggs, C. L., R. S. Niell, V. O. Ezenwa, S. Simmers, K. White, and A. Leidner. In review. Introduced hosts and native herbivores: a case of maladaptation. Evolution.

Fleishman, E., G.T. Austin, and A.D. Weiss. 1998. An empirical test of Rapoport’s rule: elevational gradients in montane butterfly communities. Ecology 79:2482–2493.

Fleishman, E., G.T. Austin, and D.D. Murphy. 2001. Biogeography of Great Basin butterflies: revisiting patterns, paradigms, and climate change scenarios. Biological Journal of the Linnean Society 74:501–515.

Fleishman, E., C.J. Betrus, R.B. Blair, R. Mac Nally, and D.D. Murphy. 2002. Nestedness analysis and conservation planning: the importance of place, environment, and life history across taxonomic groups. Oecologia 133:78–89.

Fleishman, E. and R. Mac Nally. 2003. Distinguishing between signal and noise in faunal responses to environmental change. Global Ecology and Biogeography 12:395–402.

Fleishman, E., R. Mac Nally, and J.P. Fay. 2003. Validation tests of predictive models of butterfly occurrence based on environmental variables. Conservation Biology 17:806–817.

Mac Nally, R. and E. Fleishman. 2004. A successful predictive model of species richness based on indicator species. Conservation Biology 18:646–634.

Seto, K.C., E. Fleishman, J.P. Fay, and C.J. Betrus. 2004. Linking spatial patterns of butterfly and bird species richness with Landsat TM derived NDVI. International Journal of Remote Sensing 25:4309–4324.