Intact ecological communities provide important ecosystem services including pest and disease control, clean water, coastal protection, and pollination (Millennium Ecosystem Assessment, 2005). All species exist as members of ecological communities, interacting with each other in complex ways that deeply affect their viability. Thus, biotic interactions are necessary for life on Earth. The capacity to provide important ecosystem services depends in large part on the persistence of biotic interactions. With the onset of global change, species are faced with a myriad of challenges affecting their survival. Whereas some species may adapt to these changes with shifts in phenology and ranges, and local adaptation, others experience range contractions, population declines, and even extinctions (Walther et al., 2002; Skelly et al., 2007; Williams and Jackson, 2007; Yang and Rudolf, 2010). Through species interactions, the direct effects on individual species can lead to many indirect effects on the broader community and ecosystem services.
Whereas species responded to natural climate change in the past, species today face an unusually rapid rate of climate change (Solomon et al., 2007; Marcott et al., 2013). In addition, extensive anthropogenic impacts including over-exploitation, invasive species, and habitat alteration further affect species’ ability to adapt to climatic change. With human population expected to reach 10 billion by the end of the century, demand for natural resources and the appropriation of ecosystem services will continue to increase. Yet the supply of this natural capital is limited and becoming increasingly degraded through agricultural conversion, fisheries, energy exploration, and mining. Across many types of organisms, studies have already documented significant distribution changes, altered species interactions, changes in population size, and local extinctions (Walther et al., 2002; Edwards and Richardson, 2004; Parmesan, 2006). As climate change intensifies (Solomon et al., 2007) and the human population expands, it is more important than ever to anticipate changes in ecological communities and their ecosystem services. In doing so, we can identify solutions that will promote their sustainability in an era of rapid global change.
The grand challenge is to generate robust predictions that can directly inform sustainable resource use and management of ecosystem services. Current models predicting the effects of climate change typically consider species separately and rely solely on climate and other abiotic drivers (Gilman et al., 2010; Sinclair et al., 2010; Zarnetske et al., 2012). Yet these approaches omit important interactions among species and do not consider other changes such as habitat alteration. With recent advances in species and land use datasets, and models incorporating species interactions, we have an opportunity to improve our predictions.
One way to meet this challenge is to build community-level models that account for changes in climate and land use and directly incorporate species interactions in space or time (e.g., multivariate Bayesian spatial models and autoregressive state-space models). As the rates of climate change differ among biomes (e.g., tropical vs. high latitudes), and land use varies among developing and developed countries, it is important to investigate an array of locations spanning these natural and anthropogenic gradients. Land conversion to agriculture or for direct resource extraction have some of the largest footprints on earth, yet these land uses also vary in their intensity – ranging from subsistence and permaculture farming or fishing to vast crop monocultures or ocean trawling. Thus, we should locate different regions around the world that encompass these gradients and contain sufficient data to parameterize models. A growing number of resources provide data for such models, including comprehensive global species distributions (e.g., the Map of Life: http://mappinglife.org), and land cover - land use change datasets (e.g., MODIS satellite imagery; Friedl et al., 2010).
A related challenge is identifying which species are most sensitive to these changes, and through their biotic interactions, impart the largest effect on their communities and ecosystem services. Insights from ecological theory, experiments, and field studies can help identify such key species. For example, recent research on ecological community dynamics and climate change suggests that interactions between consumers and their resources may play stronger roles in driving community responses to climate change than competitive relationships within a trophic level (Post, in press). In addition, laboratory and field warming studies have found that top consumers (predators and herbivores) are especially sensitive to climate change as compared to lower trophic levels (Petchey et al., 1999; Voigt et al., 2003). As these top consumers play vital roles in regulating many ecological communities, climate and habitat changes on these species can have especially far-reaching impacts on the rest of the community (Post and Forchhammer, 2002; Gill et al., 2009; Estes et al., 2011; Harley, 2011; Post, 2013). In essence, top consumers act as biotic multipliers of climate change (Zarnetske et al., 2012).
With these top consumers as a focus, we could build a modeling framework for each study region that encompasses the direct and indirect effects of climate and land use change. Given the array of case studies, we could identify which combinations lead to higher sensitivity to global change. For example, we expect that species’ body size, home range, dispersal ability, and evolutionary history will all be important. Whether these characteristics are consistent across land use intensity and latitude remains to be seen. Through these assessments and insights from macroecology, we can improve our understanding of which species and environment characteristics lead to higher sensitivity to global change. Related outcomes from this type of analysis include identifying barriers to dispersal and thus informing the placement of corridors and reserves.
Ecological theory can help identify how climate and land use change affects the structure and function of ecological communities, but identifying the linkage with the quality of ecosystem services is another complex problem. An interdisciplinary approach involving ecologists, climate scientists, and social scientists could tease this apart. One might expect that more intensive human impacts such as increased fertilizer and pesticide use might align with a decline in ecosystem services, and thus a change in the ecological community. Quantifying the amount of human impacts (e.g., labor, commercial fertilizers and pest control chemicals) across land use intensity gradients could be one way to measure the loss in ecosystem services. Coupling this analysis with the ecological community analysis described above would begin to identify how changes in ecological communities map to changes in ecosystem services and vice versa. In turn, this type of analysis could identify resource extraction techniques that have the least negative impact on species and may even help them adapt to a rapidly changing world.
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