Body Mass Patterns Predict Invasions and Extinctions in Transforming Landscapes

Abstract

Scale-specific patterns of resource distribution on landscapes entrain attributes of resident animal communities such that species body-mass distributions are organized into distinct aggregations. Species within each aggregation respond to resources over the same range of scale. This discontinuous pattern has predictive power: invasive species and extinct or declining species in landscapes subject to human transformation tend to be located at the edge of body-mass aggregations (P Ͻ 0.01), which may be transition zones between distinct ranges of scale. Location at scale breaks affords species great opportunity, but also potential crisis.

Biological invasions, ecological resilience and adaptive governance

“…2) (Allen et al, 1999). In particular, successfully introduced nonindigenous species occur at the edges of body size classes (Allen et al, 1999), which indicate proximity of a species' ecological niche to scale transition zones.…”

“…In particular, successfully introduced nonindigenous species occur at the edges of body size classes (Allen et al, 1999), which indicate proximity of a species' ecological niche to scale transition zones. These zones are highly variable in terms of biotic and abiotic processes (Wiens, 1989;Allen and Holling, 2010), and are also associated with other phenomena reflecting biological variability, for example: species extinctions or turnover in the community (Allen et al, 1999); higher population fluctuations (Wardwell and Allen, 2009); and decreasing fitness of individuals within a population . Species unsuccessful as invaders, alternatively, tend to have body masses that place them in the middle of size classes (Allen, 2006).…”

Functional Group Change within and across Scales following Invasions and Extinctions in the Everglades Ecosystem

“…To determine the richness of ecological functions for each body mass aggregation, we classified species by functional groups using both foraging strata (for example, aquatic, fossorial, terrestrial, arboreal/foliage, bark, and aerial) and diet (herbivorous, omnivorous, insectivorous, and carnivorous) based on published species accounts (see Forys and Allen 1999) (Table 1). Functional group richness for each aggregation was determined by simply counting the number of different foraging strata/diet combinations present in each body mass aggregation.…”

“…To test our hypotheses, we assembled species lists for each taxonomic group before and after European colonization (Forys and Allen 1999;Allen and others 1999). A species was considered to be nonnative if it was introduced to south Florida by humans, or if it had invaded south Florida since European colonization.…”

“…Species declines and extinctions have primarily resulted from habitat transformation, as well as interactions with nonnatives. Successful invasions have been aided by this same habitat transformation (Forys and Allen 1999;Allen and others 1999). For our analyses, we did not assume that all species that interact with the environment at the same scale directly interact themselves, but we did assume that invasions and extinctions are related to changes in landscape structure that result from changes in the processes that structure ecosystems at large scales.…”