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

Abstract

Cross-scale resilience theory predicts that the combination of functional diversity within scales and functional redundancy across scales is an important attribute of ecosystems because it helps these systems resist minor ecological disruptions and regenerate after major disturbances such as hurricanes and fire. Using the vertebrate fauna of south Florida, we quantified how the loss of native species and invasion by nonnatives may alter functional group richness within and across scales. We found that despite large changes in species composition due to potential extinctions and successful invasions by nonnative species, functional group richness will not change significantly within scales, there will not be any significant loss of overall redundancy of ecology function across scales, and overall body mass pattern will not undergo substantial change. However, the types of functions performed will change, and this change may have profound effects on not only the Everglades ecosystem but on the entire landscape of south Florida.

Predictors of Introduction Success in the South Florida Avifauna

“…The body mass distribution of the birds of South Florida was discontinuously distributed (Figure 3; Allen et al 1999;Forys and Allen 2002). The eight variable logistic analysis model was untenable due to quasi complete separation (no maximum likelihood estimate exists) caused by inclusion of the variable congener.…”

“…Edge distance = distance to nearest aggregation defining ''edge'' species in terms of log(10) body mass units. Raffaelli et al (2000), Havlicek and Carpenter (2001) and Forys and Allen (2002) suggest that body mass structure is conservative, robust to perturbations and large turnover in species composition. The association of invasiveness and decline (Allen et al 1999, this paper) and nomadism (Allen and Saunders 2002) with discontinuities in body mass distributions, provides compelling evidence that discontinuities are biologically important.…”

Biological invasions, ecological resilience and adaptive governance

“…An example of this scenario is the vertebrate fauna of the Everglades region in south Florida, USA. Since the 1950s vertebrates in the Everglades have experienced declines in the abundances of native species, with as much as 25% of the vertebrate fauna declining (Forys and Allen, 2002). Declining species span the size range of extant vertebrates (and therefore represent a diversity of functions over multiple scales).…”

“…The species that have successfully invaded south Florida have a great range in body mass (and size classes), and thus are present at multiple scales (and multiple size classes). However, the overall distribution of function within and across scales is largely unchanged despite extinctions and invasions, and therefore it is likely that the resilience of the system is relatively unchanged (Forys and Allen, 2002). Invasions can replace native species, but do not reduce functional group richness within scales or reduce ecological function across scales (Forys and Allen, 2002).…”

“…However, the overall distribution of function within and across scales is largely unchanged despite extinctions and invasions, and therefore it is likely that the resilience of the system is relatively unchanged (Forys and Allen, 2002). Invasions can replace native species, but do not reduce functional group richness within scales or reduce ecological function across scales (Forys and Allen, 2002). Despite a fundamental change in community composition, the pattern of ecological function within and across scales has been conserved in the Everglades vertebrate community.…”