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1. Prehistoric archives reveal evidence of predator loss and prey release in Caribbean reef fish communities

   https://doi.org/10.1073/pnas.2503986122  

   O’Dea, Aaron; Dillon, Erin M; Brandl, Simon J; Cramer, Katie L; Cybulski, Jonathan D; de_Gracia, Brígida; García-Méndez, Kimberly; Griswold, Katherine; Lin, Chien-Hsiang; Leray, Matthieu; et al (July 2025, Proceedings of the National Academy of Sciences)

   Understanding how humans have altered coral reef food webs remains challenging due to the absence of prehistoric baselines. Here, we use fish remains preserved in fossil and archaeological deposits from Panamá and the Dominican Republic to explore how Caribbean reef fish mortality patterns have changed over millennia. By quantifying accumulation rates of shark dermal denticles (scales) and bony fish otoliths (ear stones) in reef sediments, we assess relative fish abundance, while otolith size serves as a proxy for body size at death. Comparisons of these death assemblages suggest a 75% decline in shark-derived material and a 22% reduction in the sizes of human-targeted fishes—consistent with historical exploitation. This evidence of decline in large-bodied, higher trophic level fish remains coincided with a doubling in prey fish otolith accumulation and a 17% increase in their reconstructed body sizes. These patterns in time-averaged death assemblages align with effects of release from predation, documenting an often assumed (but rarely shown) cascading effect. In contrast, otoliths of predator-sheltered cryptobenthic fishes showed no change in either accumulation or size, suggesting that ‘‘bottom–up”environmental factors were not responsible for the observed changes. Together, these data indicate that pre-exploitation predator communities strongly controlled exposed prey fishes, but this “top–down” effect diminishes rapidly toward the food chain base, especially in predator-resistant groups. Understanding trophic cascades on Caribbean reefs requires studying systems before predator depletion. 

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2. A healthy but depleted herd: Predators decrease prey disease and density

   https://doi.org/10.1002/ecy.4063  

   Lopez, Laura K.; Cortez, Michael H.; DeBlieux, Turner S.; Menel, Ilona A.; O'Brien, Bruce; Cáceres, Carla E.; Hall, Spencer R.; Duffy, Meghan A. (May 2023, Ecology)

   Abstract The healthy herds hypothesis proposes that predators can reduce parasite prevalence and thereby increase the density of their prey. However, evidence for such predator‐driven reductions in the prevalence of prey remains mixed. Furthermore, even less evidence supports increases in prey density during epidemics. Here, we used a planktonic predator–prey–parasite system to experimentally test the healthy herds hypothesis. We manipulated density of a predator (the phantom midge,Chaoborus punctipennis) and parasitism (the virulent fungusMetschnikowia bicuspidata) in experimental assemblages. Because we know natural populations of the prey (Daphnia dentifera) vary in susceptibility to both predator and parasite, we stocked experimental populations with nine genotypes spanning a broad range of susceptibility to both enemies. Predation significantly reduced infection prevalence, eliminating infection at the highest predation level. However, lower parasitism did not increase densities of prey; instead, prey density decreased substantially at the highest predation levels (a major density cost of healthy herds predation). This density result was predicted by a model parameterized for this system. The model specifies three conditions for predation to increase prey density during epidemics: (i) predators selectively feed on infected prey, (ii) consumed infected prey release fewer infectious propagules than unconsumed prey, and (iii) sufficiently low infection prevalence. While the system satisfied the first two conditions, prevalence remained too high to see an increase in prey density with predation. Low prey densities caused by high predation drove increases in algal resources of the prey, fueling greater reproduction, indicating that consumer–resource interactions can complicate predator–prey–parasite dynamics. Overall, in our experiment, predation reduced the prevalence of a virulent parasite but, at the highest levels, also reduced prey density. Hence, while healthy herds predation is possible under some conditions, our empirical results make it clear that the manipulation of predators to reduce parasite prevalence may harm prey density. 

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3. Viral predation pressure on coral reefs

   https://doi.org/10.1186/s12915-023-01571-9  

   Silveira, Cynthia B.; Luque, Antoni; Haas, Andreas F.; Roach, Ty N.; George, Emma E.; Knowles, Ben; Little, Mark; Sullivan, Christopher J.; Varona, Natascha S.; Wegley Kelly, Linda; et al (December 2023, BMC Biology)

   Abstract Background Predation pressure and herbivory exert cascading effects on coral reef health and stability. However, the extent of these cascading effects can vary considerably across space and time. This variability is likely a result of the complex interactions between coral reefs’ biotic and abiotic dimensions. A major biological component that has been poorly integrated into the reefs' trophic studies is the microbial community, despite its role in coral death and bleaching susceptibility. Viruses that infect bacteria can control microbial densities and may positively affect coral health by controlling microbialization. We hypothesize that viral predation of bacteria has analogous effects to the top-down pressure of macroorganisms on the trophic structure and reef health. Results Here, we investigated the relationships between live coral cover and viruses, bacteria, benthic algae, fish biomass, and water chemistry in 110 reefs spanning inhabited and uninhabited islands and atolls across the Pacific Ocean. Statistical learning showed that the abundance of turf algae, viruses, and bacteria, in that order, were the variables best predicting the variance in coral cover. While fish biomass was not a strong predictor of coral cover, the relationship between fish and corals became apparent when analyzed in the context of viral predation: high coral cover (> 50%) occurred on reefs with a combination of high predator fish biomass (sum of sharks and piscivores > 200 g m −2 ) and high virus-to-bacteria ratios (> 10), an indicator of viral predation pressure. However, these relationships were non-linear, with reefs at the higher and lower ends of the coral cover continuum displaying a narrow combination of abiotic and biotic variables, while reefs at intermediate coral cover showed a wider range of parameter combinations. Conclusions The results presented here support the hypothesis that viral predation of bacteria is associated with high coral cover and, thus, coral health and stability. We propose that combined predation pressures from fishes and viruses control energy fluxes, inhibiting the detrimental accumulation of ecosystem energy in the microbial food web. 

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4. Climate, predation, and the controls of island lizard abundance and community structure

   https://doi.org/10.1002/ecs2.70053  

   Folfas, Edita; Mahler, D Luke; Frishkoff, Luke O (November 2024, Ecosphere)

   Abstract Alternative ecological theories make divergent predictions about the relationship between predators and their prey. If predators exert top‐down ecosystem control, increases in predation should diminish prey abundance and could either diminish or enhance community diversity of prey species. However, if bottom‐up ecosystem controls predominate, predator populations should track underlying variation in prey diversity and abundance, which ultimately should reflect available energy. Past research, both across islands and comparing islands with the mainland, has frequently invoked the importance of predation in regulating lizard abundance and diversity, suggesting an important role of top‐down control when predators are present. However, others have posited a stronger role of food limitation, via competition or bottom‐up forces. If top‐down control predominates, then negative correlations between prey abundance and predator occurrence should emerge within and among islands. Using data from eBird, we inferred landscape‐level presence data for bird species on the islands of Jamaica and Hispaniola. By summing occurrence probabilities of all known anole‐predator birds, we estimated total avian predation pressure and combined these estimates with anole community data from a mark‐recapture study that spanned spatial and climatic gradients on both islands. Avian predators and anole lizards were both affected by climate, with total predator occurrence, anole abundance and anole species richness increasing with mean annual temperature. Anole abundance and predator occurrence showed a curvilinear relationship, where abundance and predator occurrence increased together until predator occurrence became sufficiently high that anole abundance was negatively impacted. This indicates that bottom‐up ecosystem controls drive richness of both anoles and their predators, mitigating the negative effects predators might have on their prey, at least until predator occurrence reaches a threshold. We did not detect consistent evidence of predator occurrence reducing anole community richness. These findings support past research showing that islands with more predators tend to have lower prey abundances, but it does not seem that these top‐down forces are strongly limiting species coexistence. Instead, bottom‐up forces linked with climate may be more important drivers of diversity in both lizards and their avian predators on these islands. 

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5. Predator signaling of multiple prey on different trophic levels structures trophic cascades

   https://doi.org/10.1002/ecy.4050  

   Belgrad, Benjamin A.; Smee, Delbert L.; Weissburg, Marc J. (May 2023, Ecology)

   Abstract The capacity of an apex predator to produce nonconsumptive effects (NCEs) in multiple prey trophic levels can create considerable complexity in nonconsumptive cascading interactions, but these effects are poorly studied. We examined such effects in a model food web where the apex predator (blue crabs) releases chemical cues in urine that affect both the intermediate consumer (mud crabs seek shelter) and the basal prey (oysters are induced to grow stronger shells). Shelter availability and predator presence were manipulated in a laboratory experiment to identify patterns in species interactions. Then, experimentally induced and uninduced oysters were planted across high‐quality and low‐quality habitats with varying levels of shelter availability and habitat heterogeneity to determine the consistency of these patterns in the field. Oyster shell thickening in response to blue crab chemical cues generally protected oysters from mud crab predation in both the laboratory and in field environments that differed in predation intensity, structural complexity, habitat heterogeneity, and predator composition. However, NCEs on the intermediate predator (greater use of refugia) opposed the NCEs on oyster prey in the interior of oyster reefs while still providing survival advantages to basal prey on reef edges and bare substrates. Thus, the combined effects of changing movement patterns of intermediate predators and morphological defenses of basal prey create complex, but predictable, patterns of NCEs across landscapes and ecotones that vary in structural complexity. Generalist predators that feed on multiple trophic levels are ubiquitous, and their potential effects on NCEs propagating simultaneously to different trophic levels must be quantified to understand the role of NCEs in food webs. 

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