Aaron M. Ellison | bioRxiv Science

bioRxiv2016

Morphological structure of ant assemblages in tropical and temperate forests

Morphological variation in co-occurring species often is used to infer species assembly rules and other processes structuring ecological assemblages. We compared the morphological structure of ant assemblages in two biogeographic regions along two extensive latitudinal gradients to examine common patterns and unique characteristics of trait distribution. We sampled ant assemblages along extensive latitudinal gradients in Tropical Atlantic Forest in eastern Brazil and temperate forests in the eastern United States. We quantified 14 morphological traits related to the ecology and life history of each of 599 ant species and defined the morphological space occupied by different ant assemblages. Null models were used to test whether tropical and temperate ant assemblages differed from random expectation in morphological structure. Correlations between traits and climate were used to infer associations between habitat characteristics and morphological space occupied by ant assemblages. Tropical ant assemblages had higher morphological diversity and variation in the space of occupied morphospace, whereas temperate assemblages had higher variance in size. Although tropical ant assemblages had smaller morphological distances among species, species packing (i.e., mean nearest-neighbor distance) did not differ between regions. Null model analysis revealed scant evidence of habitat filtering or niche differentiation within assemblages. Different traits had different means, variances, skewness, and kurtosis values along each environmental gradient. Mean trait values within assemblages were associated mainly with region and correlated with temperature but trait variances had more complex responses to climate, including interactions between temperature and precipitation in the models. The higher functional diversity in tropical ant assemblages occurs by expansion of the morphospace rather than through an increase in species packing. Different traits vary independently along environmental gradients. Analysis of individual traits together with categorization of the moments of trait distributions (statistical central tendencies) provide new directions for quantifying morphological diversity in ant assemblages.

Ecology↗

bioRxiv2016

Metaproteomics reveals biomarkers of system collapse in a dynamic aquatic ecosystem

Forecasting and preventing rapid ecosystem state changes is important but hard to achieve without functionally relevant early warning indicators. Here we use metaproteomic analysis to identify protein biomarkers indicating a state change in an aquatic ecosystem resulting from detrital enrichment. In a 14-day field experiment, we used detritus (arthropod prey) to enrich replicate aquatic ecosystems formed in the water-filled pitcher-shaped leaves of the northern pitcher plant, Sarracenia purpurea. Shotgun metaproteomics using a translated, custom metagenomic database identified proteins, molecular pathways, and microbial taxa that differentiated control oligotrophic ecosystems that captured only ambient prey from eutrophic ecosystems that were experimentally enriched. The number of microbial taxa was comparable between treatments; however, taxonomic evenness was higher in the oligotrophic controls. Aerobic and facultatively anaerobic bacteria dominated control and enriched ecosystems, respectively. The molecular pathways and taxa identified in the enriched treatments were similar to those found in a wide range of enriched or polluted aquatic ecosystems and are derived from microbial processes that occur at the base of most detrital food webs. We encourage the use of metaproteomic pipelines to identify better early-warning indicators of impending changes from oligotrophic to eutrophic states in aquatic and other detrital-based ecosystems.

Ecology↗