Regional Turnover and Fluctuation in Populations of Five Plants Confined to Serpentine Seeps

Abstract: Spatial patterns in population turnover were analyzed for five plant species confined to a patchy and isolated habitat, serpentine seeps: annuals Helianthus exilis and Mimulus nudatus and perennials Senecio clevelandii , Astragalus clevelandii , and Delphinium uliginosum . A 3-year survey showed that, over a preceding 15-year period, 32 of 132 known populations in a 4200-ha area disappeared, and 65 new populations appeared. Populations that disappeared were significantly more isolated from conspecific populations than were surviving populations. Populations that disappeared were also marginally significantly closer to human-caused disturbances than were populations that survived. Vacant sites in which new populations appeared were significantly less isolated from conspecific populations than sites remaining vacant. Spatial patterns in population density were analyzed for three of the species for 3 years at 50 sites in a 20 × 40 km region. From 1997 to 1998, population densities of each species changed synchronously throughout the region. From 1998 to 1999, one species (   Mimulus nudatus ) again showed synchrony, and populations of the other two species (   Helianthus exilis , Delphinium uliginosum ) remained asynchronous and spatially uncorrelated. The five species we studied all appear to be persisting well at the regional scale, despite recent disturbance to the study region. These results suggest that for rare plants in isolated habitats, the spatial configuration of populations may have an important influence on local population persistence.     

Alternative prey and the dynamics of intraguild predation: theoretical perspectives

A rich body of theoretical literature now exists focused on the three-species module of intraguild predation (IGP), in which a top predator both attacks and competes with an intermediate predator. Simple models of intraguild predation are often unstable, either because one consumer is excluded, or because sustained oscillations emerge from long feedback loops. Yet, many natural IGP systems robustly persist. Standard models of intraguild predation simplify natural systems in crucial ways that could influence persistence; in particular, many empirical IGP systems are embedded in communities with alternative prey species. We briefly review the key conclusions of standard three-species IGP theory, and then present results of theoretical explorations of how alternative prey can influence the persistence and stability of a focal intraguild predation interaction.