Habitat corridors alter relative trophic position of fire ants

摘要

Habitat fragmentation disrupts species movement, leading to local extinctions and altered community structure. Habitat corridors, which connect isolated patches of habitat and facilitate movement between patches, provide a potential solution to these negative impacts. However, most studies to date have examined the movement of species alone without considering emergent effects on the community (e.g., altered trophic structure). We use large‐scale, experimental landscapes and nitrogen stable isotopes ratios (δ~(15)N) of a common generalist consumer (the fire ant, Solenopsis invicta ) to determine how corridors affect trophic structure. Thus, because the fire ant is a species whose trophic position is flexible and whose diet typically reflects local prey availability, we assume that shifts in fire ants' trophic position between connected and isolated patches are likely to reflect shifts in patch trophic structure. We found that colonies in isolated patches had lower means and ranges of δ~(15)N than colonies in otherwise similar connected patches, suggesting that corridors may increase fire ants' trophic position and breadth, respectively. Previous work in our landscapes documented higher species richness of plants in connected than unconnected patches. Patch means of ant δ~(15)N were positively correlated with plant richness, suggesting that increased plant richness may influence the observed responses in fire ant δ~(15)N. Together these results suggest that fragmentation may reduce trophic position and narrow trophic breadth of dietary generalists such as the fire ant. These shifts likely reflect an alteration of food webs in isolated patches. Our results suggest that corridors may be effective in preventing or reducing such alterations.