Disentangling the roles of biological traits and metacommunity dynamics on the multifunctional resilience of neotropical ecosystems – RESILIENCE

Our experiments are conducted in French Guiana. We use rainshelters and mesh nets to manipulate drought and metacommunity dynamics at the level of an entire, spatially-discrete ecosystem (the natural microcosm formed by rainwater-filled leaves of tank bromeliads and their microbial-faunal communities), to separate the roles of in situ recovery (tolerance, resistance forms) versus immigration on the resilience of key ecosystem functions under different drought scenarios. We define tolerance as physiological ability of current life form (e.g., larvae) to withstand drought, whereas resistance refers to a resting stage (e.g., cysts) to allow the population to persist through the dry spell. Desiccation-rehydration experiments will allow us to partition the contributions of tolerance and resistance to resilience. We will also manipulate habitat patch size and isolation, to examine how the interaction between these factors affect ecosystem resilience. Response variables will account for core functions in most ecosystems: detrital decomposition, photosynthetic activity and microbial respiration, and the simultaneous production of these functions or multifunctionality.

Extreme drought events, rather than an increase in the average duration of dry seasons (up to + 40% relative to the current norm), can wipe out entire aquatic communities. Ecosystem functions (decomposition, respiration, photosynthesis) are negatively affected by the decrease in specific richness, rather than by the physicochemical effects of drought on the aquatic system. Upon rewetting, the resilience of biological communities and ecosystem functions depend on the duration of the drought, on species’ physiological resistance to desiccation (LT50), and on immigration from preserved source patches (e.g. humid lowlands of dense forests). For environmental managers, this means that the main lever for action is the preservation of intact forests, and at a minimum, of the connectivity between intact plots that will allow dispersal of colonizers.

RESILIENCE comes at a critical point in research on ecological effects of climate change, and will provide a fresh, synthetic approach on how to predict the ecosystem consequences of climate change. If we understand the physiological, biological and ecological mechanisms that enhance or undermine multifunctional resilience, we can consider how our results will allow forecasting future responses of ecosystems to drought.

Céréghino R., Françoise L., Bonhomme C., Carrias J.F., Compin A., Corbara B., Jassey V., Leflaive J., Rota T., Farjalla V., Leroy C. 2020. Desiccation resistance traits predict freshwater invertebrate survival and community response to drought scenarios in a Neotropical ecosystem. Ecological Indicators 119 : 106839

The impacts of severe drought events on ecosystem functions are far from being understood, as are the mechanisms which underlie functional resilience after the disturbance has passed. This topic is of utmost importance in tropical regions, where climate change models forecast significant changes in water availability due to increasing frequency and intensity of drought events. Only a handful of studies have examined how drought can affect multiple functions in tropical systems. Because such studies focused on the immediate outcome of drought (ignoring the recovery and resilience trajectories), we don’t know how organism traits and ecological mechanisms mediate the post-drought trajectory of ecosystem functions. Metacommunity theory predicts that immigration from source patches should prevent extinction in sink populations, but we know nothing of how habitat patch size and distance to source populations interactively mediate ecosystem resilience to drought. The aim of RESILIENCE is to understand how different scales of biological organisation, organisms, functional community structure, metacommunity, and their interactions, drive community re-assembly and multifunctional resilience in neotropical ecosystems, following drought events that range from the current norm to extreme events and predictions of the Intergovernmental Panel on Climate Change. Our experiments will be conducted in French Guiana. We will manipulate drought and metacommunity dynamics at the level of an entire, spatially-discrete ecosystem (the natural microcosm formed by rainwater-filled leaves of tank bromeliads and their microbial-faunal communities), to separate the roles of in situ recovery (tolerance, resistance forms) versus immigration on the resilience of key ecosystem functions under different drought scenarios. We define tolerance as physiological ability of current life form (e.g., larvae) to withstand drought, whereas resistance refers to a resting stage (e.g., cysts) to allow the population to persist through the dry spell. Desiccation-rehydration experiments will allow us to partition the contributions of tolerance and resistance to resilience. We will also manipulate habitat patch size and isolation, to examine how the interaction between these factors affect ecosystem resilience. Response variables will account for core functions in most ecosystems: detrital decomposition, photosynthetic activity and microbial respiration, and the simultaneous production of these functions or multifunctionality. We expect that modest drought intensities will be resisted by the in situ tolerance traits of species, but once drought intensifies these physiological thresholds will be exceeded and the system will shift to a degraded state. At this point, continuance of the community will be dependent on recolonization from nearby source patches, and therefore metacommunity configuration will become critical. Our specific hypotheses are: (1) Multifunctionality will shift to alternative states at lower drought intensity if source patches are not available to prevent extinctions; (2) as drought intensity increases, the driving factors underlying ecosystem resilience will shift from organism tolerance to resistance, and from functional community structure to metacommunity dynamics; and (3) once we account for the negative effect of distance from source patches on recolonization rates, larger patches will be more attractive to immigrants and will undergo faster resilience than smaller habitat patches. Our findings will be disseminated to scientists, students, stakeholders, and public schools. If we understand the mechanisms that enhance or undermine multifunctional resilience, we can consider how our results will allow forecasting future responses of ecosystems to drought. RESILIENCE comes at a critical point in research on ecological effects of climate change, and will provide a fresh, synthetic approach on how to predict the ecosystem consequences of climate change.