Habitat corridors alter relative trophic position of fire ants

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 (delta-N-15) 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 delta-N-15
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 delta-N-15 were positively correlated with plant
richness, suggesting that increased plant richness may influence the
observed responses in fire ant delta-N-15. 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.