ALBERT

Beschreibung: Somatic growth dynamics are an integrated response to environmental conditions. Hawksbill sea turtles ( Eretmochelys imbricata ) are long-lived, major consumers in coral reef habitats that move over broad geographic areas (hundreds to thousands of kilometers). We evaluated spatio-temporal effects on hawksbill growth dynamics over a 33-yr period and 24 study sites throughout the West Atlantic and explored relationships between growth dynamics and climate indices. We compiled the largest ever data set on somatic growth rates for hawksbills – 3541 growth increments from 1980 to 2013. Using generalized additive mixed model analyses, we evaluated 10 covariates, including spatial and temporal variation, that could affect growth rates. Growth rates throughout the region responded similarly over space and time. The lack of a spatial effect or spatio-temporal interaction and the very strong temporal effect reveal that growth rates in West Atlantic hawksbills are likely driven by region-wide forces. Between 1997 and 2013, mean growth rates declined significantly and steadily by 18%. Regional climate indices have significant relationships with annual growth rates with 0- or 1-yr lags: positive with the Multivariate El Niño Southern Oscillation Index (correlation = 0.99) and negative with Caribbean sea surface temperature (correlation = −0.85). Declines in growth rates between 1997 and 2013 throughout the West Atlantic most likely resulted from warming waters through indirect negative effects on foraging resources of hawksbills. These climatic influences are complex. With increasing temperatures, trajectories of decline of coral cover and availability in reef habitats of major prey species of hawksbills are not parallel. Knowledge of how choice of foraging habitats, prey selection, and prey abundance are affected by warming water temperatures is needed to understand how climate change will affect productivity of consumers that live in association with coral reefs.

Beschreibung: Plant and animal diversity generally increases with increasing environmental heterogeneity. Here, we test whether this relationship also holds for bacterial communities in soil. Specifically, we investigate whether invasive annual grasslands have reduced soil heterogeneity and, thereby, decreased bacterial alpha- and beta-diversity. Soils were sampled at nine sites within a 5-km stretch of Southern California, at five depths in three habitats, including non-native invasive annual grassland, native oak woodland, and native coastal sage scrub. We characterized soil heterogeneity as well as bacterial alpha- and beta-diversity by 16S ribosomal RNA sequencing. We found that invasive annual grasslands harbored less soil heterogeneity and reduced bacterial alpha-diversity relative to the two native woody habitats. Further, across all habitats and depths, bacterial alpha- and beta-diversity was positively related to soil heterogeneity. These results suggest that plant invasions associated with soil homogenization may lead to reduced microbial diversity.