Reciprocal feedbacks between spatial subsidies and reserve networks in coral reef meta‐ecosystems

Abstract

Top-down processes such as predation and herbivory have been shown to control the dynamics of communities across a range of ecosystems by generating trophic cascades. However, theory is only beginning to describe how these local trophic processes interact with spatial subsidies in the form of material (nutrient, detritus) transport and organismal dispersal to (1) shape the structure of interconnected (meta-) ecosystems and (2) determine their optimal management via reserve networks. Here, we develop a meta-ecosystem model to understand how the reciprocal feedbacks between spatial subsidies and reserve networks modulate the importance of top-down control in a simple herbivorous fish-macroalgae-coral system. We show that in large and isolated reserve networks where connectivity between protected and unprotected areas is limited, spatial subsidies remain largely confined to reserves. This retention of spatial subsidies promotes the top-down control of corals and macroalgae by herbivores inside reserves but reduces it outside reserves. Conversely, in small and aggregated reserves where connectivity between protected and unprotected areas is high, the spillover of spatial subsidies causes a reduction in top-down control of corals and macroalgae by herbivores inside reserves and an increase in the strength of top-down control outside reserves. In addition, we demonstrate that there is a trade-off between local and regional conservation objectives when designing reserve networks: small and aggregated reserves based on the extent of dispersal maximize the abundance of corals and herbivores regionally, whereas large and isolated reserves always maximize the abundance of corals within reserves, regardless of the extent of dispersal. The existence of such "conservation traps," which arise from the fulfillment of population-level objectives within local reserves at the cost of community-level objectives at regional scales, suggests the importance of adopting a more holistic strategy to manage complex and interconnected ecosystems.

Meta-Ecosystems 2.0: Rooting the Theory into the Field

“…This is especially relevant in the context of increasing perturbations, where disruptions in local processes can spread in space through changes in spatial flows [17,[19][20][21][22]. However, while the theoretical development of the meta-ecosystem framework has been fast [13,16,[23][24][25][26][27][28][29], adoption by empiricists has generally lagged behind [11], and mostly consisted of conceptual experiments paralleling the modelling work [17,21,30] or a few applications to coastal systems [31,32].…”

Recent advances in metacommunities and meta-ecosystem theories

“…These recent studies illustrate how novel metrics of landscape heterogeneity, combined with a knowledge of spatial and species interaction strength, can lead to predictions that are tailored to specific empirical study systems. Finally, non-equilibrium meta-ecosystem theories are also relevant to conservation endeavors by predicting how the emergence of multiple scales of spatiotemporal patterns of abundance can inform decisions on the optimal size and spacing of local protected areas within regional reserve networks 66, 67 .…”

The Challenges Associated With Connectivity in Ecosystem Processes

“…We are only just beginning to realise the importance of how these processes interrelate with local species interactions to control the structure and function of meta-ecosystems (Gravel et al, 2010a). Increased spatial subsidies, due to regional climatic or anthropogenic factors, have been shown to affect the health and structure of interconnected ecosystems (Spiecker et al, 2016). The impact of source-sink dynamics associated with ecosystem functions such as nutrient cycling and sediment transport differ depending on the context, the associated habitats, and the entity in question, all of which must be accounted for when using the source-sink concept.…”