Progress 10/01/00 to 09/30/05
Outputs
Our work is directed at mitigating the negative effects of habitat loss and fragmentation on the conservation of biological diversity. This project successfully tested the effects of habitat corridors, or habitats that connect otherwise isolated areas, on plant and animal dispersal, and on their populations and biodiversity. Corridors are created to promote movement between otherwise unconnected habitat patches. Our work has provided the most comprehensive test to date of this function of corridors. We have shown that corridors increase movement rates of many different plant and animal species, and promote interactions such as pollination and seed dispersal by birds. Our experimental work at large scales has shown that corridors can be generally effective at accomplishing their intended function. A second advance we have made is to identify the mechanisms by which corridors increase movement rates among populations. In particular, his group showed that local movement
behaviors of birds, particularly along habitat edges, can be used to predict the landscape level dispersal of seeds they consume. Because local behaviors are much easier to measure than dispersal, this result suggests a promising approach to assess effects of habitat fragmentation on many species. A third advance we have made is to demonstrate the population level impacts of corridors. Our experimental research also cautioned that there may be negative effects of corridors. Because corridors create edges, they attract species that like edge habitat. However, our group found that they also attract predators, creating ecological traps for nesting bird species. Finally, we provided the first evidence that corridors function as conceived and increase plant diversity. Furthermore, we found that the causes of higher diversity vary. In particular, plants that are dispersed by animals move more frequently between connected patches. Yet, for wind dispersed species, corridors increase diversity
simply because they increase the amount of habitat edge.
Impacts
Our work has demonstrated that habitat corridors serve as animal highways for many species, restoring their ability to move through landscapes that have been heavily modified by human activities. We have shown that corridors increase dispersal by plants and animals, and increase biodiversity. Our work provides the strongest support to date that corridors may be successfully applied to conserve habitat and biodiversity in fragmented landscapes.
Publications
- Levey, D.J., B.M. Bolker, J.J. Tewksbury, S. Sargent, and N.M. Haddad. 2005. Effects of landscape corridors on seed dispersal by birds. Science 309:146-148.
- Levey, D.J., B.M. Bolker, J.J. Tewksbury, S. Sargent, and N.M. Haddad. 2005. Landscape corridors: Possible dangers? (response). Science 310:779-783.
- Brinkerhoff, R.J., N.M. Haddad, and J.L. Orrock. 2005. Corridors and olfactory predator cues affect small mammal behavior. Journal of Mammalogy 86:662-669.
- Weldon, A.J. and N.M. Haddad. 2005. The effects of patch shape on Indigo Buntings: evidence for an ecological trap. Ecology 86:1422-1431.
- Bradley, K.L., E.I. Damschen, L.M. Young, D. Kuefler, S. Went, G. Wray, N.M. Haddad, J.M.H. Knops, and S.M. Louda. 2003. Spatial heterogeneity, not visitation bias, dominates variation in herbivory. Ecology 84:2214-2221.
- Hudgens, B.R. and N.M. Haddad. 2003. Predicting which species will benefit from corridors in fragmented landscapes from population growth models. The American Naturalist 161:808-820.
- Tewksbury, J.J., D.J. Levey, N.M. Haddad, S. Sargent, J.L. Orrock, A. Weldon, B.J. Danielson, J. Brinkerhoff, E.I. Damschen, and P. Townsend. 2002. Corridors affect plants, animals, and their interactions in fragmented landscapes. Proceedings of the National Academy of Sciences 99:12923-12926.
- Sisk, T.D., and N.M. Haddad. 2002. Incorporating the effects of habitat edges into landscape models: Effective area models for management. Pp. 208-240 in J. Liu and W.W. Taylor, Integrating landscape ecology into natural resource management, Cambridge University Press, Cambridge, UK.
- Haddad, N.M., D. Tilman, and J.M.H. Knops. 2002. Long-term oscillations in grassland productivity induced by drought. Ecology Letters 5:110-120.
- Haddad, N.M., D. Tilman, J. Haarstad, M. Ritchie, and J. Knops. 2001. Contrasting effects of plant richness and composition on insect communities: a field experiment. The American Naturalist 158:17-35.
- Damschen, E.I., K.M. Rosenfeld, M. Wyer, D. Murphy-Medley, T.R. Wentworth, and N.M. Haddad. 2005. Visibility matters: increasing knowledge of women's contributions to ecology. Frontiers in Ecology and the Environment 3:212-219.
- Haddad, N.M. and J.J. Tewksbury. 2005. Low quality habitat corridors as movement conduits for two butterfly species. Ecological Applications 15:250-257.
- Haddad, N.M., D.R. Bowne, A. Cunningham, B. Danielson, D. Levey, S. Sargent, and T. Spira. 2003. Corridor use by diverse taxa. Ecology 84:609-615.
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Progress 10/01/03 to 09/30/04
Outputs
Our work is directed at mitigating the negative effects of habitat loss and fragmentation on the conservation of biological diversity. Our research program concentrates on two complementary study systems, one that is highly controlled and experimental in a managed pine forest, and the other that is more realistic to conservation because it focuses on endangered species in more natural ecosystems. Our experimental study concentrates specifically on how habitat corridors, or habitats that connect otherwise isolated areas, influence populations and biodiversity. In the past year, we have made progress in two areas. First, we investigated the effects of habitat edges and corridors on plant diversity. Expanding on previous work, we provided the first evidence that corridors function as conceived and increase plant diversity. Furthermore, we found that the causes of higher diversity vary. In particular, plants that are dispersed by animals move more frequently between
connected patches. Yet, for wind dispersed species, corridors increase diversity simply because they increase the amount of habitat edge. In another study in the same experiment, we have learned how habitat fragmentation may create ecological traps, whereby animals are attracted to habitats that actually reduce their reproductive success. We worked with Indigo Buntings, where are birds that are attracted to forest edges. In our study, we found that buntings chose habitat patches with more edge, but fledged fewer young there. One implication of this study is that human habitat alteration may trick birds into selecting bad habitat, and may accelerate population decline after habitat loss. Another implications is that corridors, that, because of their shape increase the amount of edge, may have some negative consequences for bird population success. In our studies in natural system, we ultimately hope to determine the impacts of corridors on populations of an endangered butterfly that
occurs only at Ft. Bragg. Our work would then be useful in habitat restoration for this species. To get to that point, we must work out methods for sampling populations of this rare species in a sensitive wetland habitat. To that end, we have been developing new methods for monitoring butterfly populations.
Impacts
Our work provides the most comprehensive support to date from large-scale experiments that corridors function as intended in conservation. They promote movement rates of many species of plants and animals, and may affect population sizes and dynamics. Importantly, our work demonstrates that corridors promote biodiversity in fragmented landscapes.
Publications
- No publications reported this period
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Progress 10/01/02 to 09/30/03
Outputs
Our work focuses on the effects of habitat fragmentation, and the role of habitat corridors in overcoming the negative effects of fragmentation. Our work this year has made several advances in synthesizing the effects of corridors on movement and dispersal of different species of plants and animals. We have shown that corridors positively influence dispersal of a number of species of plants and animals, and increase interactions between plants and animals, including pollination, seed dispersal, and seed predation. Importantly, we are making inroads into the consequences of corridor use for plant and animal populations, and for biodiversity. One way that we have begun to understand population responses to corridors is through analytical models. We have based our analyses on simple population models that have been enhanced to allow for dispersal between patches and mortality during dispersal. Our work has confirmed the main intuitive expectation for corridors: that by
increasing movements between habitat patches they will increase population sizes. In addition, we have found that understanding which species depend on corridors depends on a number of factors that are currently overlooked in management, including the time scale of corridor use, the nature of population dynamics, and the relative importance of corridors on increasing movement rates v. increasing survival during dispersal. We have also made some empirical progress on corridor effects on populations and communities. In work on populations of the endangered St. Francis Satyr butterfly, we are beginning to accumulate evidence to evaluate the effects of riparian corridors in promoting dispersal and population success within open wetlands that they connect. We have also found that nest success in a neotropical migrant bird, the indigo bunting, is much lower in connected patches, probably due to their shape. This highlights the need to seperate the role of corridors in increasing movement
from their role in altering edge effects, which we are able to do with our study. Finally, we have found that corridors increase plant species diversity. Corridors do this by promoting seed dispersal by birds and by wind (but not by mammals or gravity). Combined, our work provides comprehensive empirical support for the positive role of corridors in conservation.
Impacts
Our work provides the most comprehensive support to date from large-scale experiments that corridors function as intended in conservation. They promote movement rates of many species of plants and animals, and may affect population sizes and dynamics. Importantly, our work demonstrates that corridors promote biodiversity in fragmented landscapes.
Publications
- Hudgens, B.R. and N.M. Haddad. 2003. Predicting which species will benefit from corridors in fragmented landscapes from population growth models. The American Naturalist 161:808-820.
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Progress 10/01/01 to 09/30/02
Outputs
My research includes two components that together test for effects of habitat corridors on animal and plant populations. The first, an experimental corridor study at Savannah River Site, SC, included two major accomplishements. First, we completed research on studies of butterfly population responses to habitat corridors. Second, we published a major study investigating the effects of corridors on plants, animals, and their interactions. We found that corridors increase movements of insect pollinators (particularly butterflies), and that this caused higher pollination success in connected patches. In addition, seeds of fruiting plants were more likely to be dispersed to connected patches. In the second major study in my lab, we initiated work on the endangered St. Francis Satyr butterfly at Ft. Bragg, NC. Ultimately, the goal of the study is to learn how corridors and other landscape factors affect butterfly population success. Initially, however, our work must focus
on techniques for monitoring and population estimation for the butterfly.
Impacts
Our work demonstrates that corridors affect movements of plants and animals, and important interactions between plants and animals, such as seed dispersal and pollination, that are necessary to maintain healthy ecosystems. These results provide rigorous scientific support for the use of corridors in conservation within fragmented landscapes.
Publications
- Haddad, N.M., D.R. Bowne, A. Cunningham, B. Danielson, D. Levey, S. Sargent, and T. Spira. 2003. Corridor use by diverse taxa. Ecology, in press.
- Bradley, K.L., E.I. Damschen, L.M. Young, D. Kuefler, S. Went, G. Wray, N.M. Haddad, J.M.H. Knops, and S.M. Louda. 2003. Spatial heterogeneity, not visitation bias, dominates variation in herbivory. Ecology, in press.
- Hudgens, B.R. and N.M. Haddad. 2003. Which species benefit from corridors in fragmented landscapes? Predictions from population growth models. The American Naturalist, in press.
- Tewksbury, J.J., D.J. Levey, N.M. Haddad, S. Sargent, J.L. Orrock, A. Weldon, B.J. Danielson, J. Brinkerhoff, E.I. Damschen, and P. Townsend. 2002. Corridors affect plants, animals, and their interactions in fragmented landscapes. Proceedings of the National Academy of Sciences 99:12923-12926.
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Progress 10/01/00 to 09/30/01
Outputs
My work investigates the most population strategy for local and regional conservation in fragmented landscapes. Corridors are long, thin strips of habitat that connect otherwise isolated patches. They are designed to increase animal movement between the patches they connect, thus increasing population sizes and increasing biodiversity. My work provides the first large scale, experimental demonstration that corridors do increase movement rates and increase population sizes of some species. In the past year, we have made progress in five specific areas. First, we continued mark recapture studies of two butterfly species. Results from these studies allow us to estimate corridor effects on butterfly movement rates and population sizes. Specifically, we have found that corridors increase movement rates, and have effects above and beyond the effects of adding area alone. Second, my graduate students and postdocs have begun work on other insects, plants, birds, and small
mammals. Combined, this work will provide the most panoramic view to date regarding the conservation value of habitat corridors. Third, we have begun investigating the application of our experimental results to real world landscapes. At Savannah River Site, we have started investigations abundances and distributions of butterflies in openings in large landscapes, covering 80,000 ha, that are created by forest management. We are investigating whether natural corridors affect butterflies in otherwise isolated habitat areas. Fourth, and in another investigation of our results to the real world, we have begun work on an endangered butterfly, the St. Francis Satyr, at Ft. Bragg, NC. This butterfly lives in opening along streams, and we are investigating the importance of riparian areas along streams in directing movements and maintaining populations of this butterfly. Fifth, together with a postdoc, we are creating mathematical models to determine what characteristics of a species
predispose it to use corridors. In particular, we are interested in the types of behavioral, demographic, and life history characteristics might make corridors beneficial. Together with experimental results, we are developing the most comprehensive assessment of corridor effects on individuals, populations, communities, and ecosystems.
Impacts
I specifically demonstrated that many different types of species, including insects, mammals, and plants, are affected by corridors. By promoting movement of theses species between otherwise isolated patches, corridors have direct benefits on populations in fragmented landscapes. Not only did corridors affect individual species, but they affected critical interactions between plants and animals, such as pollination and seed dispersal. These results suggest that corridors should be an important part of biodiversity conservation in fragmented landscapes.
Publications
- Haddad, N.M., D. Tilman, J. Haarstad, M. Ritchie, and J. Knops. 2001. Contrasting effects of plant richness and composition on insect communities: a field experiment. The American Naturalist 158:17-35.
- Sisk, T.D., and N.M. Haddad. 2002. Incorporating the effects of habitat edges into landscape models: Effective Area Models for management. In J. Liu and W.W. Taylor, Integrating landscape ecology into natural resource management. Cambridge University Press, Cambridge, England.
- Haddad, N.M., D. Tilman, and J.M.H. Knops. 2002. Long-term oscillations in grassland productivity induced by drought. Ecology Letters 5:110-120.
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Progress 10/01/99 to 09/30/00
Outputs
no report, new project
Impacts
(N/A)
Publications
- No publications reported this period
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