Using multiple spatial scales to understand community responses to spatially and structurally shifting ecological landscapes

Background/Question/Methods

To evaluate habitat complexity as a facilitator of biodiversity, we must consider its importance relative to other factors shaping ecological communities. Natural landscapes are rarely contiguous, so even if organisms recruit to preferred habitats, their establishment also depends on regional geographic context, habitat availability, and local interactions with co-occurring species. As changing climate rearranges foundation species (e.g. mangroves displacing marshes), the relative influences of local habitat and geographic context will affect inhabitant assembly in fluctuating ecosystems. Here, I characterize marine crustacean communities inhabiting a structurally-shifting wetland ecotone along 250km (~4° of latitude) of Florida’s Atlantic coast. I used plankton tows and passive traps in spatially-nested comparisons of larval supply and settlement in mangrove and marsh habitats. I estimated species composition and distributions to evaluate the relative influences of local habitat complexity and regional geographic context on community assembly. Strong local effects could prevent functional equivalence of alternative habitats in new geographic ranges. Mixed influences of local and regional processes would likely generate novel assemblages in areas of mangrove expansion. This study evaluates the multi-scale influences of habitat complexity for the formation of communities to better understand and predict how ecological communities respond to global change.

Results/Conclusions

At least 20 marine decapod crustacean species were collected across sites with comparable salinity from 27-30°N latitude. Water temperatures decreased with latitude and sampling date. Despite differences in settlement, species supply was comparable across sites except for occasional singletons. Across sites and dates, settling species represented a subset of species supply documented in adjacent plankton tows. At southern sites, where mangroves are dominant, more species were found in mangroves (s=12; 6 unshared) than in adjacent marsh patches (s=8; 2 unshared). Along the expanding mangrove frontier, communities did not differ by habitat (s=3 [2 unshared] in mangroves, s=3 [1 unshared] in marshes). Northern frontier mangroves also hosted fewer species than in their dominant southern range (s=3 north vs. s=12 south). Widely dispersed species indicate minimal dispersal limitation and regional effects, while variation in settlement within sites and by habitat type indicates strong local structuring. Reduced habitat-based differences along the shifting frontier suggest that encroaching mangrove habitat may still be insufficient to elicit mangrove community formation. The lower diversity of mangrove inhabitants along the frontier also indicates that combined multi-scale influences will likely produce novel communities where habitat-forming species shift ranges in response to changing climate.