Biogeochemical implications of biodiversity and community structure across multiple coastal ecosystems

Small-scale experiments and theory suggest that ecological functions provided by communities become more stable with increased species richness. Whether these patterns manifest at regional spatial scales and within species-rich communities (e.g., coral reefs) is largely unknown. We quantified five biogeochemical processes, and an aggregate measure of multifunctionality, in species-rich coastal fish communities to test three questions: (1) Do previously predicted biodiversity-ecosystem-function relationships hold across large spatial scales and in highly diverse communities? (2) Can additional covariates of community structure improve these relationships? (3) What is the role of community biomass and functional group diversity in maintaining biogeochemical processes under various scenarios of species loss across ecosystem types? These questions were tested across a large regional gradient of coral reef, mangrove and seagrass ecosystems. Statistical models demonstrated that species richness and the mean maximum body size per species strongly predicted biogeochemical processes in all ecosystem types, but functional group diversity was only a weak predictor. Simulating three scenarios of species loss demonstrated that conserving community biomass alone increased the ability for communities to maintain ecosystem processes. Multifunctionality of biogeochemical processes was maintained least in simulations that conserved biomass and community structure, underscoring the relative lack of importance of community structure in maintaining multiple simultaneous ecosystem functions in this system. Findings suggest that conserving community biomass alone may be sufficient to sustain certain biogeochemical processes, but when considering conservation of multiple simultaneous biogeochemical processes, management efforts should focus first on species richness

Individual Behavior Drives Ecosystem Function and the Impacts of Harvest

Current approaches for biodiversity conservation and management focus on sustaining high levels of diversity among species to maintain ecosystem function. We show that the diversity among individuals within a single population drives function at the ecosystem scale. Specifically, nutrient supply from individual fish differs from the population average \u3e80% of the time, and accounting for this individual variation nearly doubles estimates of nutrients supplied to the ecosystem. We test how management (i.e., selective harvest regimes) can alter ecosystem function and find that strategies targeting more active individuals reduce nutrient supply to the ecosystem up to 69%, a greater effect than body size–selective or nonselective harvest. Findings show that movement behavior at the scale of the individual can have crucial repercussions for the functioning of an entire ecosystem, proving an important challenge to the species-centric definition of biodiversity if the conservation and management of ecosystem function is a primary goal

Nutrient supply from fishes facilitates macroalgae and suppresses corals in a Caribbean coral reef ecosystem

On coral reefs, fishes can facilitate coral growth via nutrient excretion; however, as coral abundance declines, these nutrients may help facilitate increases in macroalgae. By combining surveys of reef communities with bioenergetics modeling, we showed that fish excretion supplied 25 times more nitrogen to forereefs in the Florida Keys, USA, than all other biotic and abiotic sources combined. One apparent result was a positive relationship between fish excretion and macroalgal cover on these reefs. Herbivore biomass also showed a negative relationship with macroalgal cover, suggesting strong interactions of top-down and bottom-up forcing. Nutrient supply by fishes also showed a negative correlation with juvenile coral density, likely mediated by competition between macroalgae and corals, suggesting that fish excretion may hinder coral recovery following large-scale coral loss. Thus, the impact of nutrient supply by fishes may be context-dependent and reinforce either coral-dominant or coral-depauperate reef communities depending on initial community states

Nutrient limitation, bioenergetics and stoichiometry: A new model to predict elemental fluxes mediated by fishes

Energy flow and nutrient cycling dictate the functional role of organisms in ecosystems. Fishes are key vectors of carbon (C), nitrogen (N) and phosphorus (P) in aquatic systems, and the quantification of elemental fluxes is often achieved by coupling bioenergetics and stoichiometry. While nutrient limitation has been accounted for in several stoichiometric models, there is no current implementation that permits its incorporation into a bioenergetics approach to predict ingestion rates. This may lead to biased estimates of elemental fluxes.Here, we introduce a theoretical framework that combines stoichiometry and bioenergetics with explicit consideration of elemental limitations. We examine varying elemental limitations across different trophic groups and life stages through a case study of three trophically distinct reef fishes. Further, we empirically validate our model using an independent database of measured excretion rates.Our model adequately predicts elemental fluxes in the examined species and reveals species‐ and size‐specific limitations of C, N and P. In line with theoretical predictions, we demonstrate that the herbivore Zebrasoma scopas is limited by N and P, and all three fish species are limited by P in early life stages. Further, we show that failing to account for nutrient limitation can result in a greater than twofold underestimation of ingestion rates, which leads to severely biased excretion rates.Our model improved predictions of ingestion, excretion and egestion rates across all life stages, especially for fishes with diets low in N and/or P. Due to its broad applicability, its reliance on many parameters that are well‐defined and widely accessible, and its straightforward implementation via the accompanying r‐package fishflux, our model provides a user‐friendly path towards a better understanding of ecosystem‐wide nutrient cycling in the aquatic biome.A free Plain Language Summary can be found within the Supporting Information of this article.A free Plain Language Summary can be found within the Supporting Information of this article.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/162691/5/fec13618_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/162691/4/fec13618-sup-0002-AppendixS1.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/162691/3/fec13618-sup-0001-Summary.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/162691/2/fec13618-sup-0003-AppendixS2.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/162691/1/fec13618.pd

Foraging choices of vampire bats in diverse landscapes: potential implications for land use change and disease transmission

In Latin America, the common vampire bat Desmodus rotundus is the primary reservoir of rabies, a zoonotic virus that kills thousands of livestock annually and causes sporadic and lethal human rabies outbreaks. The proliferation of livestock provides an abundant food resource for this obligate blood-feeding species that could alter its foraging behaviour and rabies transmission, but poor understanding of the dietary plasticity of vampire bats limits understanding of how livestock influences rabies risk. We analysed individual- and population-level foraging behaviour by applying δ13C and δ15N stable isotope analysis to hair samples from 183 vampire bats captured from nine colonies in Peru. We also assessed the isotopic distributions of realized prey by analysing blood meals extracted from engorged bats and samples collected from potential prey species. In two adjacent but contrasting areas of the Amazon with scarce and abundant livestock, we used questionnaires to evaluate the incidence of feeding on humans. Population-level isotopic signatures suggested substantial among-site variation in feeding behaviour, including reliance on livestock in some colonies and feeding on combinations of domestic and wild prey in others. Isotopic heterogeneity within bat colonies was among the largest recorded in vertebrate populations, indicating that individuals consistently fed on distinct prey resources and across distinct trophic levels. In some sites, isotopic values of realized prey spanned broad ranges, suggesting that bats with intermediate isotopic values could plausibly be dietary specialists rather than generalists. Bayesian estimates of isotopic niche width varied up to ninefold among colonies and were maximized where wildlife and livestock were present at low levels, but declined with greater availability of livestock. In the Amazon, the absence of livestock was associated with feeding on humans and wildlife. Policy implications. We provide the first insights into the foraging behaviour of vampire bats in habitats with common depredation on humans and show how vampire bat foraging may respond to land-use change. Our results demonstrate risks of rabies transmission from bats to other wildlife and are consistent with the hypothesis that introducing livestock might reduce the burden of human rabies in high-risk communities

An ecosystem ecology perspective on artificial reef production

Artificial reefs are used around the world for many purposes, including widespread deployment to increase fishery yields. These reefs are well‐studied from a direct fisheries‐based perspective, drawing largely on traditional theory and methodological approaches from population and community ecology.Here we provide an alternative perspective using basic tenets of ecosystem ecology. We focus largely on primary production, as this ecosystem process necessarily constrains the secondary production of fish and invertebrates.We use this ecosystem ecology viewpoint to examine the long‐standing attraction/production question—do artificial reefs support ‘new’ fish production or simply attract individuals from other habitats? Central to this discussion is identifying ecological thresholds and self‐reinforcing feedbacks. For example, biological or physical processes may facilitate reaching nutrient supply thresholds where fundamental ecological dynamics are shifted, such as enhanced seagrass allocation of resources to above‐ground plant structures following aggregation of fish around reefs.Synthesis and applications. We propose that the scope for enhanced primary productivity (or other accelerated ecosystem processes) is an under‐utilized guideline that can be used to prioritize artificial reef deployment as part of broader coastal management programmes. Such an ecosystem ecology perspective may provide new insights into the ecological role of artificial reefs and guide the optimization of their deployment and management.We propose that the scope for enhanced primary productivity (or other accelerated ecosystem processes) is an under‐utilized guideline that can be used to prioritize artificial reef deployment as part of broader coastal management programmes. Such an ecosystem ecology perspective may provide new insights into the ecological role of artificial reefs and guide the optimization of their deployment and management.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/163540/2/jpe13748.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/163540/1/jpe13748_am.pd

Estimates of fish and coral larvae as nutrient subsidies to coral reef ecosystems

Nutrient subsidies are essential for the functioning of many ecosystems. A long‐standing conundrum in coral reef ecology is how these systems can be among the most productive globally, but persist in nutrient‐poor conditions. Here, we investigate the importance of the larvae of fishes and corals and gametes of corals as nutrient subsidies for coral reefs. We provide evidence that fish larvae may be an ecologically important source of exogenous nutrients. We found that at the high end of mean estimates of fish larval supply rates, larvae can replace the nutrients in the entire fish community (estimated from Caribbean coral reefs) in 28 and 434 d for nitrogen (N) and phosphorus, respectively. Coral larvae, on the other hand, appear to represent only a fraction of the nutrients supplied by the larval fish community. In contrast, coral gametes provide substantial pulses of recycled nutrients during synchronous spawning events. Within a single night, gametes from coral spawning events can produce nutrient fluxes that represent 13 and 64 times the amount of N and carbon, respectively, stored in coral reef fish communities. Our analysis suggests that larvae and/or gametes of fishes and corals may represent an important, but previously underappreciated, source of nutrients to coral reefs that warrant inclusion into models of nutrient dynamics and ecosystem function.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/144262/1/ecs22216_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/144262/2/ecs22216.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/144262/3/ecs22216-sup-0002-AppendixS2.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/144262/4/ecs22216-sup-0001-AppendixS1.pd

Taxonomic identity best explains variation in body nutrient stoichiometry in a diverse marine animal community

Abstract Animal-mediated nutrient dynamics are critical processes in ecosystems. Previous research has found animal-mediated nutrient supply (excretion) to be highly predictable based on allometric scaling, but similar efforts to find universal predictive relationships for an organism’s body nutrient content have been inconclusive. We use a large dataset from a diverse tropical marine community to test three frameworks for predicting body nutrient content. We show that body nutrient content does not follow allometric scaling laws and that it is not well explained by trophic status. Instead, we find strong support for taxonomic identity (particularly at the family level) as a predictor of body nutrient content, indicating that evolutionary history plays a crucial role in determining an organism’s composition. We further find that nutrients are “stoichiometrically linked” (e.g., %C predicts %N), but that the direction of these relationships does not always conform to expectations, especially for invertebrates. Our findings demonstrate that taxonomic identity, not trophic status or body size, is the best baseline from which to predict organismal body nutrient content

Mechanistic support for increased primary production around artificial reefs

Understanding factors controlling primary production is fundamental for the protection, management, and restoration of ecosystems. Tropical seagrass ecosystems are among the most productive ecosystems worldwide, yielding tremendous services for society. Yet they are also among the most impaired from anthropogenic stressors, prompting calls for ecosystem‐based restoration approaches. Artificial reefs (ARs) are commonly applied in coastal marine ecosystems to rebuild failing fisheries and have recently gained attention for their potential to promote carbon sequestration. Nutrient hotspots formed via excretion from aggregating fishes have been empirically shown to enhance local primary production around ARs in seagrass systems. Yet, if and how increased local production affects primary production at ecosystem scale remains unclear, and empirical tests are challenging. We used a spatially explicit individual‐based simulation model that combined a data‐rich single‐nutrient primary production model for seagrass and bioenergetics models for fish to test how aggregating fish on ARs affect seagrass primary production at patch and ecosystem scales. Specifically, we tested how the aggregation of fish alters (i) ecosystem seagrass primary production at varying fish densities and levels of ambient nutrient availability and (ii) the spatial distribution of seagrass primary production. Comparing model ecosystems with equivalent nutrient levels, we found that when fish aggregate around ARs, ecosystem‐scale primary production is enhanced synergistically. This synergistic increase in production was caused by nonlinear dynamics associated with nutrient uptake and biomass allocation that enhances aboveground primary production more than belowground production. Seagrass production increased near the AR and decreased in areas away from the AR, despite marginal reductions in seagrass biomass at the ecosystem level. Our simulation’s findings that ARs can increase ecosystem production provide novel support for ARs in seagrass ecosystems as an effective means to promote (i) fishery restoration (increased primary production can increase energy input to the food web) and (ii) carbon sequestration, via higher rates of primary production. Although our model represents a simplified, closed seagrass system without complex trophic interactions, it nonetheless provides an important first step in quantifying ecosystem‐level implications of ARs as a tool for ecological restoration.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/174782/1/eap2617_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/174782/2/eap2617.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/174782/3/eap2617-sup-0001-Appendix_S1.pd