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Invasion Rates (invasion + rate)
Selected AbstractsFrom simple rules to cycling in community assemblyOIKOS, Issue 2 2004Sebastian J. Schreiber Simulation studies of community assembly have frequently observed two related phenomena: (1) the humpty dumpty effect in which communities can not be reconstructed by "sequential" invasions (i.e. single species invasions separated by long intervals of time) and (2) cycling between sub-communities. To better understand the mechanisms underlying these phenomena, we analyze a system consisting of two predators and two prey competing for a shared resource. We show how simple dominance rules (i.e. R* and P* rules) lead to cycling between sub-communities consisting of predator,prey pairs; predator and prey invasions alternatively lead to prey displacement via apparent competition and predator displacement via exploitative competition. We also show that these cycles are often dynamically unstable in the population phase space. More specifically, while for too slow invasion rates (i.e. "sequential" invasions) the system cycles indefinitely, faster invasion rates lead to coexistence of all species. In the later case, the assembly dynamics exhibit transient cycling between predator-prey subcommunities and the length of these transients decreases with the invasion rate and increases with habitat productivity. [source] Predicting the number of ecologically harmful exotic species in an aquatic systemDIVERSITY AND DISTRIBUTIONS, Issue 2 2008Anthony Ricciardi ABSTRACT Most introduced species apparently have little impact on native biodiversity, but the proliferation of human vectors that transport species worldwide increases the probability of a region being affected by high-impact invaders , i.e. those that cause severe declines in native species populations. Our study determined whether the number of high-impact invaders can be predicted from the total number of invaders in an area, after controlling for species,area effects. These two variables are positively correlated in a set of 16 invaded freshwater and marine systems from around the world. The relationship is a simple linear function; there is no evidence of synergistic or antagonistic effects of invaders across systems. A similar relationship is found for introduced freshwater fishes across 149 regions. In both data sets, high-impact invaders comprise approximately 10% of the total number of invaders. Although the mechanism driving this correlation is likely a sampling effect, it is not simply the proportional sampling of a constant number of repeat-offenders; in most cases, an invader is not reported to have strong impacts on native species in the majority of regions it invades. These findings link vector activity and the negative impacts of introduced species on biodiversity, and thus justify management efforts to reduce invasion rates even where numerous invasions have already occurred. [source] Effects of resource availability and social parasite invasion on field colonies of Bombus terrestrisECOLOGICAL ENTOMOLOGY, Issue 3 2008CLAIRE CARVELL Abstract 1.,The survival, growth and fecundity of bumblebee colonies are affected by the availability of food resources and presence of natural enemies. Social parasites (cuckoo bumblebees and other bumblebees) can invade colonies and reduce or halt successful reproduction; however, little is known about the frequency of invasion or what environmental factors determine their success in the field. 2.,We used 48 experimental colonies of the bumblebee Bombus terrestris, and manipulated both resource availability at the landscape scale and date of colony founding, to explore invasion rates of social parasites and their effect on the performance of host colonies. 3.,Proximity to abundant forage resources (fields of flowering oilseed rape) and early colony founding significantly increased the probability of parasite invasion and thus offset the potential positive effects of these factors on bumblebee colony performance. 4.,The study concludes that optimal colony location may be among intermediate levels of resources and supports schemes designed to increase the heterogeneity of forage resources for bumblebees across agricultural landscapes. [source] From simple rules to cycling in community assemblyOIKOS, Issue 2 2004Sebastian J. Schreiber Simulation studies of community assembly have frequently observed two related phenomena: (1) the humpty dumpty effect in which communities can not be reconstructed by "sequential" invasions (i.e. single species invasions separated by long intervals of time) and (2) cycling between sub-communities. To better understand the mechanisms underlying these phenomena, we analyze a system consisting of two predators and two prey competing for a shared resource. We show how simple dominance rules (i.e. R* and P* rules) lead to cycling between sub-communities consisting of predator,prey pairs; predator and prey invasions alternatively lead to prey displacement via apparent competition and predator displacement via exploitative competition. We also show that these cycles are often dynamically unstable in the population phase space. More specifically, while for too slow invasion rates (i.e. "sequential" invasions) the system cycles indefinitely, faster invasion rates lead to coexistence of all species. In the later case, the assembly dynamics exhibit transient cycling between predator-prey subcommunities and the length of these transients decreases with the invasion rate and increases with habitat productivity. [source] Control of plant species diversity and community invasibility by species immigration: seed richness versus seed densityOIKOS, Issue 1 2003Rebecca L. Brown Immigration rates of species into communities are widely understood to influence community diversity, which in turn is widely expected to influence the susceptibility of ecosystems to species invasion. For a given community, however, immigration processes may impact diversity by means of two separable components: the number of species represented in seed inputs and the density of seed per species. The independent effects of these components on plant species diversity and consequent rates of invasion are poorly understood. We constructed experimental plant communities through repeated seed additions to independently measure the effects of seed richness and seed density on the trajectory of species diversity during the development of annual plant communities. Because we sowed species not found in the immediate study area, we were able to assess the invasibility of the resulting communities by recording the rate of establishment of species from adjacent vegetation. Early in community development when species only weakly interacted, seed richness had a strong effect on community diversity whereas seed density had little effect. After the plants became established, the effect of seed richness on measured diversity strongly depended on seed density, and disappeared at the highest level of seed density. The ability of surrounding vegetation to invade the experimental communities was decreased by seed density but not by seed richness, primarily because the individual effects of a few sown species could explain the observed invasion rates. These results suggest that seed density is just as important as seed richness in the control of species diversity, and perhaps a more important determinant of community invasibility than seed richness in dynamic plant assemblages. [source] | ||||||||||