RESEARCH INTERESTS AND GOALS, Donald Winslow, September 2013
Habitat and landscape structure affect demographic parameters of biological populations. Spatial and temporal patterns of climate, topography, and vegetation are inherently dynamic. This is as true as ever today, as human industry alters all of these aspects of our world and the patterns and pace of change itself. Environmental change, in turn, feeds back to influence human society.
Patterns of natural and anthropogenic disturbance affect vegetation structure over fine and broad spatial scales. The quality of an animal's habitat depends on the structure, community composition, and age of plants both near and far from its home range. We must understand how biological populations respond to various environmental factors and disturbance regimes if we wish to maximize the conservation of diversity through the current transition period. Future populations and communities (ecological and human) depend on the taxonomic, genetic, and cultural diversity that we can maintain today.
Prescribed fire and succession of grassland-breeding birds
Fire and grazing have influenced Great Plains prairie communities since the last glacial retreat. European colonists changed the timing, frequency, intensity, and quality of these disturbances (Reinking, 2005). These changes may pose problems for grassland bird populations.
Several years ago I employed an experimental approach to observe the effects of fire on grassland bird populations in west-central Oklahoma (Winslow, 2008). In 2006 and 2007 I surveyed breeding bird communities at 24 points at the Grazinglands Research Laboratory at Ft. Reno where fields are burned every few years to promote cattle forage. Six of these points were in fields that were burned in April 2007. I compared counts of three obligate grassland-breeding species in burned and unburned fields. For burned and unburned groups of points, I calculated the ratio of the mean abundance per point for each of these three species in 2007 to the mean abundance per point in 2006. If fire affects the abundance of a species in the succeeding breeding season, we would expect this ratio to differ between burned and unburned fields for that species.
Although mean abundance of Dickcissels (Spiza americana) declined from 2006 to 2007 at unburned points, mean abundance increased between these two years in burned fields. As a result, the between-year ratio for this species was higher in burned fields than in unburned fields. A bootstrapping analysis reveals this difference is statistically significant. In general, counts for Eastern Meadowlarks (Sturnella magna) and Northern Bobwhite (Colinus virginianus) were lower the second year. This trend may simply reflect that the survey dates were later in the breeding season during 2007, as a result of flooding and other logistical constraints. For both of these species, between-year ratios were lower in burned sites than in unburned sites.
These data suggest frequent burns may increase abundances of some grassland-obligate bird species in the year following a fire. Other species (such as the Eastern Meadowlark and the Northern Bobwhite) may decline in the season following a fire. More data are needed to draw firm conclusions.
I completed counts at the same survey points in 2008, after more fields had been burned.
Short-term goal: Compare results of grassland bird surveys from 2008 with those of earlier years to more fully understand avian community dynamics over the course of a fire cycle.
Long-term goal: Continue to monitor bird populations before and after prescribed burns and throughout the fire cycle in order to understand how fire and grazing affect grassland bird populations.
Factors responsible for population declines of grassland-breeding birds
Wilcove and coworkers (1998) examined factors affecting populations of species federally listed in the USA as threatened or endangered. They concluded that habitat loss and degradation constitute the greatest threat for imperiled species. This conclusion has been widely cited and broadly applied. It has been widely assumed, for instance, that habitat loss and alteration has been responsible for declines in populations of grassland-breeding birds.
Mineau and Whiteside (2013), however, recently published evidence suggesting that poisoning from pesticides better explains population declines of grassland-breeding birds in the USA than does intensity of agricultural land use. Other variables that may influence grassland bird populations include reforestation, fire suppression, habitat fragmentation, cattle grazing, changes in food supply resulting from pesticide use, nest predation, and brood parasitism by Brown-headed Cowbirds (Molothrus ater).
Long-term goal: Develop a research program to distinguish among the various factors that may be responsible for declines of North American grassland-breeding bird populations.
Forest fragmentation and demography of breeding birds
In 2003 I completed a doctorate in ecology at Indiana University. My dissertation research addressed effects of forestry practices on the breeding success of songbirds in south-central Indiana. Our research group observed substantial variation in breeding success across forest contexts (Winslow et al., 2000), but these patterns were not always consistent among years. This uncertainty was exacerbated by a lack of theoretical guidance.
Although many published studies examine effects of habitat edges on avian nest success (whether edge effects occur), few address mechanisms underlying such edge effects (why edge effects occur). It is thus risky to apply results from one setting to other landscapes characterized by different ecological communities and types of anthropogenic disturbance.
My dissertation project, funded principally by the National Fish and Wildlife Foundation, addressed these weaknesses in the understanding of edge effects on avian productivity by (1) presenting a series of simple analytic models to describe possible mechanisms explaining edge effects (Winslow, 1999), (2) using experimental techniques to evaluate the effects of forest management practices on numbers and nest success of various species of breeding birds, and (3) developing statistical approaches to test mechanistic hypotheses about edge effects.
We need to understand the bases for observed patterns, so we must design studies to test mechanistic hypotheses and analyze data using statistical models that are appropriate for the questions at hand.
Short-term goal--Develop a robust and unbiased bootstrap approach to contrast avian nest success rates. Use the bootstrapping approach to re-examine data from my experimental investigation of forestry impacts on breeding birds. Revise the manuscript from this study and submit it for publication.
Long-term goal: Initiate a program to study forestry impacts on boreal forest breeding birds.
Effects of forest pests on breeding bird habitat
In 2004 I contributed to a research project addressing the potential effects of a novel tree disease, sudden oak death, on faunal populations in California coastal oak woodland. Policy decisions concerning commerce can have important consequences for the spread of forest pathogens and other invasive organisms. Tree diseases can affect forest community composition and structure over broad areas. These changes may cascade to influence faunal communities.
Sudden oak death, a tree disease caused by the oomycete Phytophthora ramorum, has caused high levels of adult tree mortality in western coastal ecosystems. This disease may spread to near and distant regions and dramatically alter vegetation structure in multiple forest communities. The apparent increase in the frequency of El Niño events may help P. ramorum to expand its range south along the coast. Resulting changes in vegetation structure and tree community composition could influence vertebrate community composition and other ecosystem attributes.
My colleagues and I evaluated candidate models of habitat association for species of mammals, birds, reptiles, and amphibians in order to predict effects of sudden oak death on vertebrate communities. I developed generalized linear mixed models of cavity-nesting bird habitat association to simulate future avian community trajectories in diseased coast live oak woodland.
Renewable energy impacts on avian populations
There is a broadly recognized need for society to move from non-renewable energy sources to sustainable alternatives. However, increasing energy supply enables humans to engage in destructive behaviors on a larger scale. How do we build renewable technology while maintaining biodiversity?
There are technical and cultural components to this problem. On the technical side, development of alternative energy industries often has direct impacts on biological populations. Large-scale wind farms fragment habitat for sensitive grassland-breeding birds and contribute directly to mortality through avian collisions. Bioenergy development has the potential to transform broad regions of functional forest habitat to biologically depauperate plantations.
Culturally, without a shift in values the expansion of our energy supply will continue to increase consumption of resources and degradation of habitat. Increasingly, ecological economists have argued that we should shift from a culture of consumption-driven growth to a stable economy. Otherwise, we stand poised to undermine the resources and services with which our Earth sustains us.
Long-term goal: Extend my investigation of habitat disturbance to address the impacts of renewable energy sources on bird populations.
Mineau, P.; and M. Whiteside. 2013. Pesticide acute toxicity is a better correlate of U.S. grassland bird declines than agricultural intensification. PLoS ONE 8(2):e57457, doi:10.1371/journal.pone.0057457, http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0057457.
Reinking, D. L. 2005. Fire regimes and avian responses in the central tallgrass prairie. Studies in Avian Biology 30:116-126.
Wilcove, D. S.; D. Rothstein; J. Dubow; A. Phillips; and E. Losos. 1998. Quantifying threats to imperiled species in the United States. BioScience 48(8):607-615.
Winslow, D.E. 1999. Mechanistic approaches to the investigation of edge effects on avian productivity. Current Ornithology 15:262-309.
Winslow, D. E. 2003. The effects of forest management practices on reproductive success of Neotropical migrant birds in south-central Indiana, Ph.D. dissertation, Indiana University, Bloomington, IN.
Winslow, D. E. 2008. Grassland bird response to fire in fields managed for cattle forage. 93rd Ecological Society of America Annual Meeting, Milwaukee, WI (abstract), http://esameetings.allenpress.com/2008/P14698.HTM.
Winslow, D. E.; D. R. Whitehead; C. Frazer Whyte; M. A. Koukol; G. M. Greenberg; and T. B. Ford. 2000. Within-landscape variation in patterns of cowbird parasitism in the forests of south-central Indiana. In Smith, J.N.M.; T.L. Cook; S.I. Rothstein; S.K. Robinson; and S.G. Sealy (eds). The Ecology and Management of Cowbirds and their Hosts: Studies in the Conservation of North American Passerine Birds. University of Texas Press, Austin.