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Disease emergence and biodiversity loss are two of the most pressing environmental challenges of the modern era. Each is driven predominantly by human-mediated alterations in the environment. Although changes in biodiversity and infectious diseases have often been studied separately, the importance of interactions between them has received comparatively little attention. Under what circumstances will disease epidemics drive species losses? And, reciprocally, can higher levels of biodiversity reduce parasite transmission (i.e., the dilution effect) or lead to increases in infection (i.e., the amplification effect)? Through what ecological mechanisms and at what magnitude relative to other pathways known to affect parasite spread, such as changes in host density?
Humans, wildlife and domestic animals are often intimately linked through shared infection. Nearly 70% of emerging infections in humans involve non-human hosts or vectors, while growing evidence indicates that human infections are increasingly spilling into wildlife populations (e.g., measles in gorillas, tuberculosis in African elephants). These observations underscore the importance of research to systematically tackle the pathways of transmission for multi-host pathogens and identify their consequences for public health and conservation.
Despite the ubiquity of parasites and pathogens in all ecosystems, our understanding of their significance in mediating predator-prey interactions, primary production, energy flow and nutrient cycling is severely limited. To better comprehend the ‘hidden’ influence of parasites in community and ecosystem ecology, we use two empirical host-parasite systems from freshwater habitats: trematode parasites in pond communities and fungal pathogens of lake zooplankton. Our goal is to answer a deceptively simple question: what would a world without parasites look like?
Ongoing emergence of infectious diseases has prompted heightened interest in understanding the ecological drivers of infection. In wildlife, for instance, infections ranging from salmonid whirling disease to crayfish plague have had devastating effects in managed and wild populations of aquatic organisms. Often a major impediment to developing better models for forecasting patterns of emergence and disease spread is the relative rarity of multi-scale databases on parasites, particularly for infections of non-human hosts. Currently our group is exploring several questions related to disease macroecology, including the spread of infections from human to wildlife hosts, the large-scale drivers of bird mortality events, mechanisms underlying the relationship between the logmean and logvariance of infection, and spatiotemporal patterns in parasite richness and disease hotspots in aquatic ecosystems.
High-elevation aquatic ecosystems are among the most vulnerable to climate change and other forms of disturbance, yet few long-term records offer sufficient resolution to characterize shifts in ecosystem structure and their underlying mechanisms. We are part of the Niwot Ridge Long-Term Ecological Research program managed by the University of Colorado, which includes one of the longest-running sampling efforts of alpine aquatic systems. The Green Lakes Valley is a 2.3 km2 catchment, named for a series of paternoster lakes that contribute drinking water for the City of Boulder, includes lakes ranging in elevation from 3216 m (Silver Lake) to 3620 m (Green Lake 5). Green Lake 4 (GL4) in particular, which is the second highest lake in the valley, has been extensively monitored for nearly three decades (http://niwot.colorado.edu).
Our group uses parasite-induced malformations in amphibians as a model system to investigate how environmental change affects the levels of disease pathology. Currently we seek to understand how different forms of environmental change, including pollution (e.g., nutrient and pesticide runoff), climate change, and biodiversity loss, affect parasite abundance and the frequency of malformations. An additional yet no less important priority is to identify the consequences of such pathology for amphibian population persistence.
Freshwater ecosystems are in the midst of a biodiversity crisis, with more threatened or extinct species than terrestrial and marine ecosystems combined. Human-mediated introductions of nonindigenous species, including invasive predators, pathogens, and competitors, are a major contributor to these alarming patterns. In many cases, however, the mechanisms through which invaders affect native biota, and how multiple forms of environmental change interact with one another, remain poorly understood. Working in aquatic ecosystems, we strive to understand (i) the environmental factors that moderate the introduction, persistence and spread of invaders and (ii) the consequences of such invasions for native species, ecological communities, and ecosystem processes in freshwaters.
Most contemporary emerging disease threats involve multiple host species, and almost all hosts are infected with more than one parasite species. Nonetheless, much of disease ecology has historically focused on interactions between a single host and parasite species, despite growing evidence that changes in host and pathogen community structure can sharply influence host pathology, parasite evolution, and the efficacy of proposed management strategies.
Climate change is projected to influence the dynamics and distributions of many parasitic diseases of both humans and wildlife. Whether such changes will serve to increase or reduce disease depends on the differential thermal physiologies of parasites and their hosts. Available forecasts suggest that climate change will involve changes in both mean temperature and temperature variability, yet relatively little is known about how shifts in temperature affect parasite-host relationships.
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