Conservation of aquatic environments: A meta-ecosystem approach
Recent estimates indicate that 80% of the world's population is exposed to a high level of threat to water security. Throughout the world, population growth translates into increased needs for food and natural resources that threaten the diversity and services provided by aquatic ecosystems. This situation leads to a paradox where denser populations that require more ecosystem services threaten the stability of aquatic ecosystems that support those services they need. A long-standing question in conservation biology is, how can we conserve aquatic ecosystems in the context of land use intensification?
Recent estimates indicate that 80% of the world's population is exposed to a high level of threat to water security. Throughout the world, population growth translates into increased needs for food and natural resources that threaten the diversity and services provided by aquatic ecosystems. This situation leads to a paradox where denser populations that require more ecosystem services threaten the stability of aquatic ecosystems that support those services they need. A long-standing question in conservation biology is, how can we conserve aquatic ecosystems in the context of land use intensification?
Predicting the impacts of anthropogenic land disturbances on aquatic ecosystems requires a better understanding of inter-ecosystem dynamics. Essentially, one needs to be able to understand i) how disturbances propagate through aquatic food webs ii) how these community-level changes translate into functional changes at the scale of ecosystem processes and iii) ultimately how these functional changes cascade in space to affect an entire watershed in terms of diversity, functioning, but also the provision of ecosystem services for human communities. This last point emphasizes the probable interaction between a very localized disturbance, the specific structure of the affected biotic community as well as the spatial configuration of the watershed which will necessarily constrain the zone of influence of this disturbance (Figure 1).
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).
My research program therefore aims to predict the cross-ecosystem impacts of anthropogenic disturbances on biodiversity and the functioning of ecosystems at the watershed scale using the conceptual tools offered by the theory of metacommunities and metaecosystems. The heart of my research program is currently divided into 3 sub-objectives:
1. Characterization of spatial variations in terrestrial-aquatic links. In aquatic ecosystems, spatial feedbacks with terrestrial systems are well recognized. On the other hand, the study of flows between ecosystems has mainly focused on the dynamics localized at the level of the ecotone, thus generally ignoring the functional implications of these feedbacks between ecosystems at spatial extents larger than the ecotone itself. However, this is essential to fully understand the larger-scale impacts of disturbances occurring at a given location in the watershed (Figure 1). Recent data from our lab suggest that regional attributes such as position in the watershed (connectivity) and habitat size may play a key role in determining the sensitivity of ecosystems to disturbance. In this context, this sub-objective aims to fill this significant lack of knowledge by implementing a long-term monitoring platform of the spatial and temporal variations in the quantity/quality (stoichiometry) of subsidies between terrestrial and aquatic ecosystems.
2. Link between anthropogenic disturbances and spatial cascades. Most of the work on the effect of subsidies between ecosystems focuses on the receiving ecosystem and considers inputs as externalities. Although the concept of spatial cascade has never been formally tested, there are empirical examples demonstrating that a change in ecosystem processes at a given location (“donor” ecosystem) can have a significant impact on the functioning of connected ecosystems (e.g., the case of snow geese affecting arctic ecosystems or logging that affects aquatic communities). Spatial cascades therefore have important implications for the propagation of the effect of disturbances in a watershed. However, we still lack a formal understanding of when and how changes in a “donor” ecosystem might spread to neighboring ecosystems. This objective therefore essentially aims to test the mechanisms by which a transformation in a “donor” system can possibly affect the functioning of a “recipient” system.
3. Implications for watershed conservation and management. This objective aims to establish partnerships with the public, NGO or private sector to develop conservation or management tools related to the expertise developed within the framework of our research program. Ultimately, we hope that our experimental and empirical research will allow us to identify areas of conservation priority in watersheds according to their location and their sensitivity to variations in terrestrial subsidies.