Publications from earlier studies of the original experimental landscape project on the Savannah River Site (SRS). These studies are by the PI's or other cooperators that used the experimental system for experiments with other species. Also included are landscape ecology studies of a related nature done by the PI's elsewhere on the SRS.

Haddad, N.M. 1999. Corridor use predicted from behaviors at habitat boundaries. American Naturalist 153:215-227.

Abstract - Through empirical studies and simulation, I demonstrate how simple behaviors can be used in lieu of detailed dispersal studies to predict the effects of corridors on interpatch movements. Movement paths of three butterfly species were measured in large (1.64 ha) experimental patches of open habitat, some of which were connected by corridors. Butterflies that "reflected" off boundaries between open patches and the surrounding forest also emigrated from patches through corridors at rates higher than expected from random movement. This was observed for two open-habitat species, Eurema nicippe and Phoebis sennae; however, edges and corridors had no effect on a habitat generalist, Papilio troilus. Behaviorally-based simulation models, which departed from correlated random walks only at habitat boundaries, predicted that corridors increase interpatch movement rates of both open-habitat species. Models also predicted that corridors have proportionately greater effects as corridor length increases, that movement rates increase before leveling off as corridor width increases, and that corridor effects decrease as patch size increases. This study suggests that corridors direct movements of habitat-restricted species and that local behaviors may be used to predict the conservation potential of corridors in fragmented landscapes.

Haddad, N.M. 1999. Corridor and distance effects on interpatch movements: a landscape experiment with butterflies. Ecological Applications 9:612-622.

Abstract - The hypothesis that corridors increase animal movement between habitat fragments, a central tenet of conservation biology, has been virtually untested. This study demonstrates that corridors increase interpatch movement rates of two butterfly species. The hypothesis was tested in a large-scale, replicated experiment, where 27 equal-sized (1.64 ha), patches of early successional habitat were created within large areas of pine forest. Patches varied in whether of not they were connected to another patch by a corridor, and in their distance from other patches (64-384 m). The results of mark-release-recapture studies showed that two open-habitat butterfly species, Junonia coenia and Euptoieta claudia, moved more frequently between patches connected by corridors than between unconnected patches. Interpatch movement was significantly, negatively related to interpatch distance. Interpatch movement rates of J. coenia were significantly, positively related to the density of its host and nectar resource, Linaria canadensis. Corridor effects were stronger for males than females, and were most pronounced within three days after butterflies were marked. Pine forest was not a complete barrier to butterfly movement; both species moved between unconnected patches, even at the longest distances. However, the results of this study suggest that corridors will increase long distance movements of habitat-restricted species.

Haddad, N.M. and K. Baum. 1999. An experimental test of corridor effects on butterfly densities. Ecological Applications 9:623-633.

Abstract - In a large-scale experiment, we found that three habitat-restricted butterfly species reached higher densities in patches connected by corridors than in similar, isolated patches. We conducted our study in 27 equal-sized (1.64 ha) patches that varied in whether or not they were connected to another patch by a corridor. Patches and corridors were open, early-successional habitat that contrasted strongly with the surrounding pine forest. Of four butterfly species studied, three open-habitat specialists (Junonia coenia, Euptoieta claudia, and Phoebis sennae) reached higher densities in patches connected by corridors than in isolated patches. A fourth species, Papilio troilus, showed no preference for open habitat or pine forest, and its density did not differ in connected or isolated patches. While butterfly densities were often significantly, positively associated with densities of host plant or flower resources, plant densities did not confound corridor effects on butterfly densities.

Higher densities in patches connected by corridors may have been caused by three different factors. First, species with higher densities in connected patches also moved more frequently between connected patches, and higher interpatch rates may have helped to sustain higher population sizes. Second, species with higher densities in connected patches also had higher densities further from the forest edge. Corridors increased the area of a patch that was further from the forest edge, which increased the "effective area" of connected patches, and may have increased butterfly densities. Third, corridors may have acted as "drift fences," intercepting dispersers from the surrounding forest and directing them to connected patches. We could not determine the relative contribution of each factor, and it is possible that all three contributed to higher densities of habitat-restricted butterflies in patches connected by corridors.

Bowne, D.R., J.D. Peles, and G.W. Barrett. 1999. Effects of landscape spatial structure on movement patterns of the hispid cotton rat (Sigmodon hispidus). Landscape Ecology 14:53-65.

Danielson, B.J. and Anderson, G.S. 1998. Habitat selection in geographically complex landscapes. Chapter in The Ecology of Small Mammals at the Landscape Level. Barrett, G.W. and Peles, J.D. (eds.). Springer-Verlag Press, in press. - No abstract

Danielson, B.J. and Hubbard, M.J. in press. The influence of corridors on the movement behavior of individual Peromyscus polionotus in experimental landscapes. Landscape Ecology

Abstract - To assess corridor effects on movement in Peromyscus polionotus (old-field mice), we used a set of three experimental landscapes that contained multiple patches (1.64 ha) of usable, open habitat embedded in a loblolly pine (Pinus taeda) forest matrix. Some patches were connected by corridors and others were isolated (unconnected). We introduced mice to nest boxes in experimental patches and followed them through the landscapes via trapping. We found weak evidence that the presence of corridors decreased the probability that P. polionotus (particularly females) would disperse or disappear from a patch. In the process of live trapping the patches, we also encountered "feral" P. polionotus, Sigmodon hispidus (cotton rats), and Peromyscus gossypinus (cotton mice). The average number of feral animals did not differ between isolated and connected patches. This suggests that corridors do not act as drift fences that "sieve" individuals out of the matrix and into the patches. However, more male than female P. polionotus and S. hispidus were trapped in isolated patches. This intersexual difference did not exist in connected patches.

Anderson, G.S. and Danielson, B.J. 1997. The effects of landscape composition and physiognomy on metapopulation size: the role of corridors. Landscape Ecology 12: 261-271.

Abstract - We develop and analyze a model that examines the effects of corridor quality, quantity, and arrangement on metapopulation sizes. These ideas were formerly investigated by Lefkovitch and Fahrig (1985) and Henein and Merriam (1990). Our simulations provide results similar to the Henein and Merriam model, indicating that the quality of corridors in a landscape and their arrangement will influence the size of a metapopulation. We then go one step further, describing how corridor arrangement alters the metapopulation, and provide a method for predicting which corridor arrangements should support larger metapopulations. In contrast to the Henein and Merriam model, we find that the number of corridor connections has no influence on the size of a metapopulation in a landscape unless there is an accompanying change in the uniformity of the distribution of corridor connections among patches.

Bird studies on the experimental landscapes or elsewhere on the SRS

Levey, D. J. and Sargent, S. 1999. A simple method for tracking vertebrate-dispersed seeds. Ecology (in press).

Abstract - Tracking vertebrate-dispersed seeds from parent plant to deposition site remains a primary obstacle to understanding the ecological and evolutionary consequences of seed dispersal. We evaluate a new and simple technique for tracking seeds. Fluorescent microspheres (15µm diameter) are applied to fruits and later recovered in fecal material associated with the fruits' seeds. Trials with captive Cedar Waxwings (Bombycilla cedrorum) demonstrated that percent recovery of microspheres is high, all defecations containing seeds also contain microspheres, relatively few microspheres are recovered in defecations not containing seeds, and presence of microspheres on fruits does not affect fruit choice. Field trials with five species of fruits demonstrated that after approximately 30 d under full sun and high temperatures, photodegradation limits one's ability to detect microspheres, that an anti-transpirant applied with the microspheres allows them to adhere to fruits without deterring fruit consumption or damaging fruits, and that microspheres can be found in fecal samples of wild birds. Our technique is likely applicable to any study in which it is necessary to link fecal material with a particular source of food or an individual animal.

Dunning, J.B., Danielson, B.J., Watts, B.D., Liu, J., and Kremetz, D.G. In press. Studying wildlife at local and landscape scales: Bachman's Sparrows at the Savannah River Site, South Carolina. Studies in Avian Biology.

Abstract - In the lat 1980s and early 1990s, mutual research interests between land managers at the Savannah River Site and biologist at the University of Georgia resulted in a landscape-ecology study of the Bachman's Sparrow (Aimophila aestivalis). This species had been declining throughout its range for several decades and was considered a species of management concern by the U.S. Forest Service. The reasons for its decline were obscure, but the distribution of suitable habitat across complex landscape was a a possible factor. Thus, the species seemed well suited for a pioneer study on landscape influences on avian population dynamics. A cooperative research program developed from these mutual interest, including quantifying the landscape and local habitat patterns shown by the sparrow, spatially explicit modeling of population response to landscape change and demographic field studies of reproductive success, survivorship, and dispersal. These studies are summarized, and the value of the research to both management and research interests is discussed.

15 June 1999