Landscape perspective on ecosystem functioning
Ecologists often seek to understand and predict the dynamic and functions of whole ecosystems. However, the ecosystems we identify for conservation purposes do not occur in isolation, they are connected via resource / nutrient flows to other ecosystems and by species movements. Metaecosystem theory has been proposed specifically as a framework to study flows across coupled ecosystems, while stressing how spatial and temporal changes in biodiversity affect ecosystem function. Empirically, the study of cross-ecosystem exchange or allochthonous subsidy has mainly focused on dynamics at the ecotone, thus generally ignoring the functional implications of metaecosystem dynamics at broader spatial extents than the ecotone itself. While theory exists but remains scarce, predicting the impact of terrestrial land-use change on aquatic ecosystems at the watershed scale would require a spatial and temporal characterization of terrestrial-aquatic linkages that simply do not exist at the moment. Yet, the effect of altering resource flows at one location is likely to propagate or even accumulate across entire ecosystems driving mesoscale variation in ecosystem function (Figure 1). In watersheds, for instance, different cross-ecosystem flows (e.g., litterfall, fish migration) will contribute differently and at different spatial extents to secondary production, but the combination of their effects should predict secondary production at the whole watershed scale. This cross-scale integration of cross-ecosystem subsidy and spatial dynamics is a critical gap to understanding and predicting whether and how anthropogenic perturbations influence regional-scale variations of biodiversity and ecosystem function in natural ecosystems (Figure 1). Research in the Meta-Ecology lab at Université de Montréal aims at filling this gap by using conceptual tools from metacommunity and metaecosystem theories.
Fig. 1 (a) Cross-ecosystem resources subsidize local aquatic communities, but their effect can also indirectly cascade in space either passively through the downstream movement of detritus and nutrients, or actively when larger consumers couple different locations along the watershed. In total, the sum result of those species interactions in space is the efficient regulation of algae despite agricultural runoffs. This leads to positive outcomes for recreational services and water quality. (b) Alterations to the quality or quantity of those cross-ecosystem subsidies can disrupt downstream algae regulation leading to eutrophication issues, loss of recreational services and poor water quality. This scenario illustrates how the effects of several stressors (i.e., wood harvesting upstream and agricultural runoffs downstream) along the watershed can potentially accumulate and disrupt key community-level interactions leading to loss of functions and services. (c) These dynamics occur within a regional context (watershed) that can be represented by a multi-layered spatial network allowing the study of how localized flow affect the whole watershed (Adapted from Harvey et al., 2016 and Harvey et al., 2020).