• Eutrophication homogenizes shallow lake macrophyte assemblages over space and time

      Salgado, J; Sayer, CD; Brooks, SJ; Davidson, TA; Goldsmith, B; Patmore, IR; Baker, AG; Okamura, B (Ecological Society of America, 2018-09-11)
      Eutrophication is commonly implicated in the reduction in macrophyte species richness in shallow lakes. However, the extent to which other more nuanced measures of macrophyte diversity, such as assemblage heterogeneity, are impacted concurrently by eutrophication over space and time and the joint influences of other factors (e.g., species invasions and connectivity) remains relatively poorly documented. Using a combination of contemporary and paleoecological data, we examine how eutrophication influences macrophyte assemblage heterogeneity and how nutrient enrichment interacts with watercourse connectivity, lake surface area, and relative zebra mussel abundance over space (within and among lakes) and time (decades to centuries) at the landscape scale. The study system is the Upper Lough Erne, Northern Ireland, UK, which is composed of a large main lake and several smaller satellite lakes that vary in their hydrological connectivity to the main lake. By applying homogeneity analysis of multivariate dispersions and partial redundancy analysis, we demonstrate that contemporary lake macrophyte heterogeneity and species richness are reduced in lakes with intensified eutrophication but are increased in lakes with greater zebra mussel abundance and lake surface area. Watercourse connectivity positively influenced assemblage heterogeneity and explained larger proportions of the variation in assemblage heterogeneity than local environmental factors, whereas variation in species richness was better related to local abiotic factors. Macrophyte fossil data revealed within- and among-lake assemblage homogenization post-1960, with the main lake and connected sites showing the highest rates of homogenization due to progressive eutrophication. The long-term and contemporary data collectively indicate that eutrophication reduces assemblage heterogeneity over time by overriding the importance of regional processes (e.g., connectivity) and exerts stronger pressure on isolated lakes. Our results suggest further that in connected lake systems, assemblage heterogeneity may be impacted more rapidly by eutrophication than species richness. This means that early effects of eutrophication in many systems may be underestimated by monitoring that focuses solely on species richness and is not performed at adequate landscape scales.
    • Mammalian tolerance to humans is predicted by body mass: evidence from long-term archives.

      Crees, JJ; Turvey, ST; Freeman, R; Carbone, C (Ecological Society of America, 2019-06-08)
      Humans are implicated as a major driver of species extinctions from the Late Pleistocene to the present. However, our predictive understanding of human-caused extinction remains poor due to the restricted temporal and spatial scales at which this process is typically assessed, and the risks of bias due to "extinction filters" resulting from a poor understanding of past species declines. We develop a novel continent-wide dataset containing country-level last-occurrence records for 30 European terrestrial mammals across the Holocene (c.11,500 years to present), an epoch of relative climatic stability that captures major transitions in human demography. We analyze regional extirpations against a high-resolution database of human population density (HPD) estimates to identify species-specific tolerances to changing HPD through the Holocene. Mammalian thresholds to HPD scale strongly with body mass, with larger-bodied mammals experiencing regional population losses at lower HPDs than smaller-bodied mammals. Our analysis enables us to identify levels of tolerance to HPD for different species, and therefore has wide applicability for determining biotic vulnerability to human impacts. This ecological pattern is confirmed across wide spatiotemporal scales, providing insights into the dynamics of prehistoric extinctions and the modern biodiversity crisis, and emphasizing the role of long-term archives in understanding human-caused biodiversity loss. This article is protected by copyright. All rights reserved.
    • Parasites lost: using natural history collections to track disease change across deep time

      Harmon, A; Littlewood, DTJ; Wood, CL (Ecological Society of America, 2019-03-04)
      Recent decades have brought countless outbreaks of infectious disease among wildlife. These events appear to be increasing in frequency and magnitude, but to objectively evaluate whether ecosystems are experiencing rising rates of disease, scientists require historical data on disease abundance. Specimens held in natural history collections represent a chronological archive of life on Earth and may, in many cases, be the only available source of data on historical disease patterns. It is possible to extract information on past disease rates by studying trace fossils (indirect fossilized evidence of an organism's presence or activity, including coprolites or feces), sequencing ancient DNA of parasites, and examining sediment samples, mummified remains, study skins (preserved animal skins prepared by taxidermy for research purposes), liquid‐preserved hosts, and hosts preserved in amber. Such use of natural history collections could expand scientific understanding of parasite responses to environmental change across deep time (that is, over the past several centuries), facilitating the development of baselines for managing contemporary wildlife disease.