Showing papers by "Earl E. Werner published in 2003"

A review of trait-mediated indirect interactions in ecological communities

Abstract: In this paper we review the empirical studies documenting trait-mediated indirect interactions (TMIIs) in food webs. Basic models and empirical approaches that form the foundation of our conceptualization of species interactions generally assume that interactions are an intrinsic property of the two interacting species and therefore are governed by their respective densities. However, if a species reacts to the presence of a second species by altering its phenotype, then the trait changes in the reacting species can alter the per capita effect of the reacting species on other species and, consequently, population density or fitness of the other species. Such trait-mediated indirect interactions can reinforce or oppose density-mediated effects and have been largely overlooked by community ecologists. We first briefly develop the case for the broad mechanistic basis for TMIIs and then review the direct evidence for TMIIs in various permutations of simple three- to four-species food webs. We find strong evid...

Estimating Decline and Distributional Change in Amphibians

Abstract: Concern over species declines has prompted researchers to use historical data as a basis for com- parison with present-day information from the same sites to assess changes in presence/absence distribu- tions. A review of the literature revealed that these resurveys typically lasted for 1 or 2 years, and many were based on museum records or other data relying on known historical presences. Using data on nine amphib- ian species from a set of 32 ponds at the E. S. George Reserve (ESGR) in Michigan, we evaluated the impor- tance of the duration of a resurvey and the type of historical data used (information on historical presences and absences vs. historical presences only). We compared data we collected between 1996 and 2000 with in- formation from the same ponds collected between 1967 and 1974. By systematically degrading the 1996- 2000 data, we determined that a resurvey lasting 1 year would yield an estimated 45% decline in the number of presences, whereas a resurvey lasting 2 years would yield an estimated 28% decline. In contrast, a 5-year resurvey would yield an estimated 3% decline in the number of presences. In addition, when our historical data were limited to known presences in the past, even a 5-year resurvey yielded an estimated 30% decline in the number of presences. Our results suggest that estimates of decline and distributional change can be ex- tremely sensitive to the duration of resurvey effort and the type of historical data used. The pattern we found in analyses of ESGR data is echoed in published studies in which multiple-year resurveys tended to yield smaller estimates of decline than single-year resurveys. Based on our findings, we suggest that future resur- veys extend for long enough to estimate the value of additional data and that geographic scales of inference be chosen based on the amount and quality of historical information.