Abstract
ABSTRACTVery small islands, on the order of a few hundred square metres in area, have rarely been the focus of ecological investigations. I sampled nine such islands in the central Exumas, Bahamas for arthropod species abundance and diversity using a combination of pitfall traps, pan traps and sticky traps. Three islands had no terrestrial vegetation, three islands contained only Sesuvium portulacastrum L., a salt‐tolerant perennial that had been experimentally introduced 10 years ago, and three islands supported one or two naturally occurring plant species. A relatively diverse arthropod assemblage was discovered, including representatives of 10 different orders of Crustacea and Insecta. Land hermit crabs were the most abundant crustaceans, and dipterans were the most abundant and speciose insects. Two of the most common insects were previously undescribed species. Measures of arthropod species abundance and diversity were not significantly different for vegetated vs. non‐vegetated islands. All 10 orders were present on bare islands, and nine of them were present on vegetated islands. Measures of arthropod species abundance and diversity were positively associated with island area, and negatively associated with distance from the nearest large island. Hypothesized food webs consist of several trophic levels and have strong allochthonous inputs. Tiny islands such as these hold insights into early successional processes and the base of insular food webs.
Highlights
The Bahamas Archipelago contains hundreds of islands, many are no more than mere ‘rocks’
One pitfall trap was inadvertently placed below the high tide line on an island, and the day was filled with seawater and thimble jellyfish, Linuche unguiculata (Schwartz)! Yet a surprising diversity of arthropod life was found on these tiny islands
All 10 orders of arthropods were present on bare islands, and nine of the 10 were present on vegetated islands, indicating that all could survive on islands lacking terrestrial vegetation
Summary
Oceanic islands represent excellent model systems for the study of many ecological patterns and processes, such as population persistence and turnover (Schoener, 1991; Morrison, 2002a, 2003; Schoener et al, 2003), food web ecology (Schoener, 1989; Polis & Winemiller, 1996; Polis et al, 2004), succession (Bush & Whittaker, 1991; Thornton, 1996) and resistance and resilience of populations to disturbance (Whittaker, 1995; Spiller et al, 1998; Schoener et al, 2001, 2004). Many studies have addressed various ecological questions on oceanic islands, few investigators have focused on very small islands (on the order of a few hundred square metres in area). Such islands may be overlooked because they appear to harbour few or no terrestrial species, or because they are difficult to access by boat (i.e. no protected harbour). Represent some of the simplest and least disturbed (by humans) ecosystems on the planet These islands hold insights into early successional processes and the base of insular food webs. The following questions were addressed: (1) What are the arthropod species abundances and diversities on these tiny islands? (2) How do arthropod species abundances and diversities vary with the presence or absence of terrestrial plant species? (3) Are standard island variables (i.e. area, distance and elevation) good predictors of arthropod species abundance and diversity on tiny islands? and (4) What is the basic structure of food webs on these islands?
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