Determinants of Species Abundance
Determinants of Species Abundance Distribution in Insect Communities and Assemblages
Using a theoretical model to describe species abundance distribution is an effective tool for both characterizing and comparing the structure of plant and animal assemblages. The logseries and the lognormal distributions are among the most common theoretical distributions used in studies of communities and assemblages. Although the logseries distribution is considered by some to be the best model for depicting species abundance distribution and thus relatively widespread, others have questioned whether it is an accurate and widespread depiction of species abundance, compared to the lognormal distribution. Some contends that often the logseries is observed because of sampling biases produced by small sample size and underrepresentation of scarce species. Previous research in our lab has characterized and compared two macrolepidopteran assemblages, on two riparian tree species, black willow Salix nigra (Marsh) and box elder Acer negundo L., that are comprised of scarce species. The structure of these assemblages parallels that of an assemblage described by a logseries distribution. However, since the characterization of the assemblages was based on relative sampling of larval abundance rather than absolute sampling, it was still subject to the criticism that the fit to the logseries was a consequence of sampling bias. Such unbiased (absolute sampling) data on the abundance of larvae of species on box elder and black willow were provided by fogging tree canopies (Barbosa et al., submitted) and demonstrated that the logseries best described species abundance distribution.
Theoretically, a lognormal distribution is assumed to arise when multiple factors determine species abundance distribution in natural communities or assemblages, even though the factors may be, and usually are, unknown. In contrast, a logseries distribution presumes that single factors determine abundance distribution. The two that are most obvious broad sense factors are the influence of natural enemies (top-down forces) or plant quality (bottom-up forces). Thus, the critical question in this research project is, Do top-down, bottom-up, or both factors influence species abundance distribution? Specifically, we focus on the box elder macrolepidopteran assemblage in order to test three alternative hypotheses, i.e., that (1) The presence and impact of natural enemies on an array of species in the macrolepidopteran assemblage on Acer negundo (box elder) determines survival and abundance and thus species abundance distribution (i.e., the structure) of the assemblage, (2) Resource quality (in the form of host plant quality) determines growth and survival and thus species abundance distribution (i.e., the structure) of the assemblage on box elder, or (3) Both natural enemies and host plant quality jointly determine the levels of survival and abundance and, thus, the species abundance distribution (i.e., the structure) of the assemblage on box elder.
Participants: P. Barbosa/A. Caldas
Using a theoretical model to describe species abundance distribution is an effective tool for both characterizing and comparing the structure of plant and animal assemblages. The logseries and the lognormal distributions are among the most common theoretical distributions used in studies of communities and assemblages. Although the logseries distribution is considered by some to be the best model for depicting species abundance distribution and thus relatively widespread, others have questioned whether it is an accurate and widespread depiction of species abundance, compared to the lognormal distribution. Some contends that often the logseries is observed because of sampling biases produced by small sample size and underrepresentation of scarce species. Previous research in our lab has characterized and compared two macrolepidopteran assemblages, on two riparian tree species, black willow Salix nigra (Marsh) and box elder Acer negundo L., that are comprised of scarce species. The structure of these assemblages parallels that of an assemblage described by a logseries distribution. However, since the characterization of the assemblages was based on relative sampling of larval abundance rather than absolute sampling, it was still subject to the criticism that the fit to the logseries was a consequence of sampling bias. Such unbiased (absolute sampling) data on the abundance of larvae of species on box elder and black willow were provided by fogging tree canopies (Barbosa et al., submitted) and demonstrated that the logseries best described species abundance distribution.
Theoretically, a lognormal distribution is assumed to arise when multiple factors determine species abundance distribution in natural communities or assemblages, even though the factors may be, and usually are, unknown. In contrast, a logseries distribution presumes that single factors determine abundance distribution. The two that are most obvious broad sense factors are the influence of natural enemies (top-down forces) or plant quality (bottom-up forces). Thus, the critical question in this research project is, Do top-down, bottom-up, or both factors influence species abundance distribution? Specifically, we focus on the box elder macrolepidopteran assemblage in order to test three alternative hypotheses, i.e., that (1) The presence and impact of natural enemies on an array of species in the macrolepidopteran assemblage on Acer negundo (box elder) determines survival and abundance and thus species abundance distribution (i.e., the structure) of the assemblage, (2) Resource quality (in the form of host plant quality) determines growth and survival and thus species abundance distribution (i.e., the structure) of the assemblage on box elder, or (3) Both natural enemies and host plant quality jointly determine the levels of survival and abundance and, thus, the species abundance distribution (i.e., the structure) of the assemblage on box elder.
Participants: P. Barbosa/A. Caldas
