Colonization and extinction of ant communities in a fragmented landscape

Abstract

In this paper we tested the assumption that smaller and more isolated remnants receive fewer ant colonizers and lose more species. We also tested hypotheses to explain such a pattern. We sampled ants in Brazil for 3 years in 18 forest remnants and in 10 grasslands between them. We tested the influence of remnant area and isolation on colonization rate, as well as the effect of remnant area on extinction rate. We tested the correlation between remnant area and isolation to verify the landscape design. Colonization rate was not affected by remnant area or isolation. Extinction rate, however, was smaller in larger remnants. Remnant area and isolation were negatively correlated. We tested two hypotheses related to the decrease in ant species extinction rate with increased remnant area: (i) small remnants support smaller and more extinction‐prone populations; and (ii) small remnants are more often invaded by generalist species, which suffer higher extinction inside remnants. The density of ant populations significantly increased with area. Generalist species presented a lower colonization rate in larger remnants, contrary to the pattern observed in forest species. Generalist species suffered more extinction than expected inside remnants. The lack of response of colonization rate to remnant area can be explained by the differential colonization by generalist and forest species. The decrease of ant population density in smaller remnants could be related to loss of habitat quality or quantity. The higher colonization by generalist ant species in the smaller remnants could be related to landscape design, because smaller remnants are more similar to the matrix than larger ones. Our results have important implications for conservation strategies because small remnants seem to be more affected by secondary effects of fragmentation, losing more forest species and being invaded more often by generalist species. Studies that compare only species richness between remnants cannot detect such patterns in species composition.

Effect of fragmentation, habitat loss and within-patch habitat characteristics on ant assemblages in semi-arid woodlands of eastern Australia

“…Thus, previously reported fragmentation effects on ant species (e.g. Suarez et al 1998;Sobrinho et al 2003;Schoereder et al 2004) may largely be demonstrating independent and joint effects of within-patch habitat characteristics associated with fragmented states, rather than the sole effects of fragmentation per se. Indeed, our findings support Abensperg-Traun et al 's (1996) conclusions that habitat characteristics were stronger predictors of arthropod communities than landscape structure in E. salubris woodlands in southwestern Australia.…”

Canopy cover negatively affects arboreal ant species richness in a tropical open habitat

“…In some places in the candeial (some of our plots), e.g. in those microhabitats with high canopy cover, generalist and opportunistic ant species are reduced or excluded, as they are better adapted to the incidence of high sunlight and high temperature of open areas (Schoereder et al, 2004;Binckley and Resentarits, 2009;Pike et al, 2011). Some of the negative relationships between environmental heterogeneity and species richness may also occur due to increases in energy costs in the mobility of animals in denser habitats.…”

Confounding factors in the detection of species responses to habitat fragmentation

“…1 A ; Fahrig, 2003). Reduced habitat area in a landscape leads to a decrease in the size of fragments and an increase in fragment isolation (Andrén, 1994), with consequent reductions in population size and colonisation rates that directly increase the risk of local extinctions (Bowers & Matter, 1997 ;Bender, Contreras & Fahrig, 1998 ;Hanski, 1998 ;Crooks et al, 2001 ;Hames et al, 2001 ;Schoereder et al, 2004). Furthermore, in a recent review, Fahrig (2003) demonstrated the impact of habitat loss on several measures of community structure including species richness, the strength of species interactions and trophic chain length in food webs, as well as on several measures of population structure, including population distribution and abundance, dispersal, reproductive output, foraging success and genetic diversity.…”