Figure 45.15 The Theory of Island Biogeography Can Be Tested
In the late 1960s, Daniel Simberloff and Edward O. Wilson were the first to test the theory of island biogeography experimentally. Specifically, the ecologists tested the theory that there is an equilibrium of species on islands, determined by the rate of immigration of new species and rate of extinction of already-established species. To test this idea experimentally, they needed islands that lacked species; as this was not possible naturally, they first needed to remove the fauna on several islands. They selected for defaunation seven islands in Florida Bay, each of varying distances and direction from larger islands. The larger islands could serve as immigration sources. The islands were small, ranging only 11 to 18 meters in diameter, and consisted solely of red mangrove trees. Prior to defaunation, they identified and counted the resident arthropods, which encompassed between 20 and 50 species. The research team then erected scaffolding and tents to enclose each island. They fumigated the islands with methyl bromide, a chemical that kills arthropods, but does not harm plants. After eradication of the islands’ arthropods by this method, they periodically monitored the recolonization of arthropods. Although species turnover rates were high, arthropods rapidly recolonized the defaunated islands, and after less than a year all but the island farthest from the mainland had approximately the same number of species as before defaunation. Note, however, that the islands returned to the same number of species, not necessarily the same species themselves. Based on these results, Simberloff and Wilson concluded that the islands supported an equilibrium number species, a result consistent with the theory of island biogeography. Simberloff and Wilson’s colonization experiment was conducted over a time period of around one year. Further, the researchers focused their efforts only on arthropod populations. These experimental conditions were sufficient to study recolonization following defaunation for a limited number of species, but not long enough to assess the full impact of additions and extinctions on species richness.
Original Papers
Simberloff, D. S., and E. O. Wilson. 1969. Experimental zoogeography of islands: The colonization of empty islands. Ecology 50: 278–296.
http://www.jstor.org/stable/1934856
Wilson, E. O., and D. S. Simberloff. 1969. Experimental zoogeography of islands: Defaunation and monitoring techniques. Ecology 50: 267–278.
http://www.jstor.org/stable/1934855
Links
Holt, R. D. 2006. Making a virtue out of a necessity: Hurricanes and the resilience of community organization. Proceedings of the National Academy of Sciences 103: 2005–2006.
http://dx.doi.org/10.1073/pnas.0600289103
Schoener, T. W., and D. A. Spiller. 2006. Nonsynchronous recovery of community characteristics in island spiders after a catastrophic hurricane. Proceedings of the National Academy of Sciences 103: 2220–2225.
http://dx.doi.org/10.1073/pnas.0510355103
University of Arizona: Ecology 438: Island Biogeography
http://www.geo.arizona.edu/Antevs/ecol438/lect13.html
Stanford University: Island Biogeography
http://www.stanford.edu/group/stanfordbirds/text/essays/Island_Biogeography.html
McGlynn, T. 2010. Effects of Biogeography on Community Diversity. Nature Education Knowledge 1(8): 32.
http://www.nature.com/scitable/knowledge/library/effects-of-biogeography-on-community-diversity-13260138
Harpole, W. 2010. Neutral Theory of Species Diversity. Nature Education Knowledge 1(8): 31.
http://www.nature.com/scitable/knowledge/library/neutral-theory-of-species-diversity-13259703
Figure 45.18 Species Richness Can Enhance Wetland Restoration
Joy Zedler and colleagues working in the Tijuana Estuary in southern California tested the hypothesis that, with regard to wetland restoration, plant biomass and nitrogen accumulation would increase more rapidly in species-rich plantings than in species-poor plantings. To test this hypothesis, some plots were planted with only one of each of the eight plant species typical of wetlands in the area, while other plots were planted with randomly chosen assemblages of either three or six species. The investigators planted the same density of seedlings in all plots, and replanted and weeded as necessary to compensate for early death of young seedlings. Results of the study showed that individual species differed in their capacity to increase biomass and nitrogen accumulation depending on whether they were planted alone or with other species. For example, Salicornia virginica and Jaumea carnosa contributed the greatest biomass when planted alone, while Triglochin concinna exhibited the highest nitrogen concentrations. Overall, however, the results showed a positive correlation between the percentage of vegetation cover and the number of species within the plots. Similarly, there was a positive correlation between the number of canopy layers and the number of species within the plots. Finally, the results also demonstrated that stored nitrogen was higher in plots with more species as opposed to plots with fewer species. Together, these findings indicated that vegetation cover, canopy complexity, and nitrogen accumulation are enhanced by species richness. Thus, this study suggested that for wetland restoration attempts, a rich mixture of species should be planted. Wetlands restoration research is particularly relevant in Louisiana, especially in the aftermath of hurricanes Katrina and Rita. These 2005 hurricanes demolished miles of coastal wetlands in the state. Given that approximately 40 percent of the total coastal wetlands of the lower 48 U.S. states are located in Louisiana, it is essential that we work to restore this important coastal ecosystem. To do so, it is vital that we not only provide the funding necessary to accomplish this enormous task, but also implement restoration techniques garnered from current research findings, such as those described above.
Original Paper
Callaway, J. C., G. Sullivan, and J. B. Zedler. 2003. Species-rich plantings increase biomass and nitrogen accumulation in a wetland restoration experiment. Ecological Applications 13: 1626–1639.
http://dx.doi.org/10.1890/02-5144
Links
Zedler, J. B. 2005. Restoring Wetland Plant Diversity: A Comparison of Existing and Adaptive Approaches. Wetlands Ecology and Management 13: 5–14.
http://dx.doi.org/10.1007/s11273-003-5014-y
University of Wisconsin: Department of Botany: The Zedler Lab: Wetland Plant Ecology
http://www.botany.wisc.edu/zedler/
Tijuana Estuary Tidal Restoration Program
http://trnerr.org/tijuana-estuary-tidal-restoration-program/
Environmental Protection Agency: River Corridor and Wetland Restoration
http://www.epa.gov/owow/wetlands/restore/
USGS: National Wetlands Research Center: Native Plants for Effective Coastal Wetland Restoration
http://www.nwrc.usgs.gov/factshts/090-03.pdf
USGS: National Wetlands Research Center
http://www.nwrc.usgs.gov/
Science Daily: Wetlands Restoration Not A Panacea For Louisiana Coast
http://www.sciencedaily.com/releases/2008/09/080924190637.htm
PBS NewsHour: Louisiana Struggles to Maintain, Improve Wetlands
http://www.pbs.org/newshour/bb/science/jan-june06/wetlands_4-3.html
Original Papers for Apply the Concept, p. 886
Simberloff, D. S. and E. O. Wilson. 1969. Experimental zoogeography of islands: The colonization of empty islands. Ecology 50: 278–296.
http://www.jstor.org/pss/1934856
Simberloff, D. S. 1976. Species turnover and equilibrium island biogeography. Science 194(4265):572-578.
http://www.jstor.org/pss/1742997
Glasser, J. W. 1982. On the causes of temporal change in communities: Modification of the biotic environment. The American Naturalist 119(3):375-390. (See Figure 7)
http://www.jstor.org/stable/2460935