Patterns and processes in insular floras affected by hurricanes

Abstract

Aim: To investigate species compositions, rates of species turnover, species-area and species-distance relationships and patterns of nestedness in the floras of small Bahamian islands, by comparing two groups of islands that had been differentially affected by two hurricanes.

Location: Small islands occurring on either side of Great Exuma near Georgetown, Bahamas.

Methods: We surveyed the plant species of 44 small islands over a 5-year period from 1998 to 2002. Hurricanes Lili and Michelle occurred in 1996 and 2001, respectively; both storms affected small islands on the more exposed south-west side of Great Exuma to a greater degree than small islands on the more protected north-east side. A set of 27 islands was surveyed in 1998 and 2002 to evaluate species turnover. Stepwise multiple linear regression analyses and an information-theoretic approach (the Akaike information criterion) were used to elucidate the importance of area and distance as predictors of plant species number. We compared a piecewise linear regression model with a simple linear regression of species number against area to determine whether a small island effect existed. Nestedness patterns were evaluated by Wilcoxon two-sample tests to analyse occurrence sequences.

Results: Species turnover was low in an absolute sense (overall = 0.74% year-1), yet was over three times higher than that documented in a nearby archipelago in the absence of hurricanes. Both vegetated area and distance were important predictor variables for exposed islands but not for protected islands. Some support was found for a small island effect for the exposed islands based on a piecewise linear regression model. Both island groups revealed significant nestedness at the level of the assemblage (both P < 0.001). On exposed islands, 65-79% (depending upon the method of calculation) of all species were significantly nested, but only 47% of all species were significantly nested on protected islands.

Main conclusions: Overall, these insular floras seem highly resistant to hurricane-force disturbances. Species turnover was low (< 1% year -1) in an absolute sense, particularly in comparison with rates for other taxa. Higher degrees of nestedness and significant species-area and species-distance relationships for exposed islands indicated stronger patterns of community assembly. It is likely that disturbance is a major structuring force for the exposed islands, although the type of disturbances that mediate these patterns may not be primarily hurricane-force storms.

Department(s)

Biology

Document Type

Article

DOI

https://doi.org/10.1111/j.1365-2699.2008.01910.x

Keywords

Akaike information criterion, Bahamas, Disturbance, Hurricane, Insular floras, Island biogeography, Nestedness, Plants, Small island effect, Species-area relationship

Publication Date

9-1-2008

Journal Title

Journal of Biogeography

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