Effects of prey characteristics on the feeding behaviors of an apex marine predator, the California moray ( Gymnothorax mordax)

The environment to the rescue: can physics help predict predator-prey interactions?

Understanding the factors that determine the occurrence and strength of ecological interactions under specific abiotic and biotic conditions is fundamental since many aspects of ecological community stability and ecosystem functioning depend on patterns of interactions among species. Current approaches to mapping food webs are mostly based on traits, expert knowledge, experiments, and/or statistical inference. However, they do not offer clear mechanisms explaining how trophic interactions are affected by the interplay between organism characteristics and aspects of the physical environment, such as temperature, light intensity or viscosity. Hence, they cannot yet predict accurately how local food webs will respond to anthropogenic pressures, notably to climate change and species invasions. Herein, we propose a framework that synthesises recent developments in food-web theory, integrating body size and metabolism with the physical properties of ecosystems. We advocate for combination of the movement paradigm with a modular definition of the predation sequence, because movement is central to predator-prey interactions, and a generic, modular model is needed to describe all the possible variation in predator-prey interactions. Pending sufficient empirical and theoretical knowledge, our framework will help predict the food-web impacts of well-studied physical factors, such as temperature and oxygen availability, as well as less commonly considered variables such as wind, turbidity or electrical conductivity. An improved predictive capability will facilitate a better understanding of ecosystem responses to a changing world.

Marine Protection Induces Morphological Variation in the California Moray, Gymnothorax mordax

The effectiveness of marine protected areas (MPAs) on the general health and conservation of species, habitats, and community interactions is of great interest to researchers, managers, and recreationalists. However, the ecological and behavioral diversity of vertebrate predators of southern California kelp forests limits our ability to make general conclusions about MPA effectiveness across a variety of species. Identifying and studying species with extreme feeding habits or prey-capture strategies may offer greater insight into predator-prey relationships and reveal the trophic importance of an animal in the larger community. Moray eels (family Muraenidae) have been shown to have morphological and behavioral adaptations that allow them to consume large prey whole, identifying them as important predators. From 2015 to 2018, we studied the health and feeding behavior of a long-lived, elusive, and benthic kelp forest predator, the California moray eel (Gymnothorax mordax). We trapped eels inside and outside of Blue Cavern Onshore State Marine Conservation Area, an MPA on the northwest side of Santa Catalina Island, CA which prohibits the take of any species. Over 4 years, we captured 1736 eels. Overall, we found that morays were longer, older, heavier, had higher body condition, and were found in greater abundance within the MPA. Although fish comprised the majority of their summer diet, morays outside of the MPA were consuming a more diverse set of fish, while kelp bass comprised more than half of the diet for morays inhabiting the MPA. Additionally, we found that morays within the MPA had larger relative vertical gape distances (VGDs) and narrower heads. Our recapture data support the high site fidelity of morays, indicating that their diet and morphology are influenced by their local community. While the majority of morays are thriving in the MPA, as suggested by their robust sizes and longevity, high abundance appears to result in higher frequencies of cannibalism, the presence of an undescribed disease, and lower growth rates. Our results suggest that the MPA affects the life history of morays and may select for an alternative feeding strategy in which eels develop larger VGDs, smaller adductor muscles, and a specialized diet which is presumably influenced by the local environment. In addition, observations of cannibalistic behavior and species-specific disease provide us with important insight into natural factors that may still regulate populations removed from anthropogenic disturbances such as fishing.

Body shape transformations by alternate anatomical adaptive peak shifts in blenniiform fishes

Extreme body elongation has occurred repeatedly in the evolutionary history of ray-finned fishes. Lengthening of the anterior-posterior body axis relative to depth and width can involve changes in the cranial skeleton and vertebral column, but to what extent is anatomical evolution determined by selective factors and intrinsic constraints that are shared broadly among closely related lineages? In this study, we fit adaptive (Ornstein-Uhlenbeck) evolutionary models to body shape and its anatomical determinants and identified two instances of extreme elongation by divergent anatomical peak shifts in the Blenniiformes, a radiation of small-bodied substrate-associated marine teleost fishes. Species in the genus Xiphasia (hairtail blennies) evolved toward a peak defined by a highly elongated caudal vertebral region but ancestral cranial and precaudal vertebral morphology. In contrast, a clade that includes the genera Chaenopsis and Lucayablennius (pike and arrow blennies) evolved toward a peak with a long slender skull but ancestral axial skeletal anatomy. Neither set of anatomical peak shifts aligns closely with the major axis of anatomical diversification in other blenniiform fishes. These results provide little evidence that ancestral constraints have affected body shape transformation, and instead suggest that extreme elongation arose with distinct shifts in selective factors and development.

Do predators react differently to dangerous and larger prey? The case of a mygalomorph generalist spider preying upon insects

Prey morphology and size are known to influence a predator's decision to attack and consume particular prey; however, studies that evaluate both traits simultaneously are uncommon. Here, we first described the trophic niche in the mygalomorph spider Paratropis sp. These spiders have a narrow trophic niche and feed mainly on sympatric species such as larvae of lepidopterans and of beetles such as carabids, passalids and scarabeids. Second, we evaluated the effect of prey taxon and size on acceptance and immobilization duration, and built an ethogram of the predator's behaviors. For each prey taxa, we offered large (approximately same size than the spider) and small larvae (approximately half of the size of the spider) of the aforementioned prey. We classified carabid beetle larvae as the most dangerous prey because of their sharp mandibles and predatory habits, followed by scarabeid larvae; lepidopteran and passalids larvae were considered to be non-dangerous prey. We did not find a significant effect of prey taxon or size on spiders' acceptance. Prey size did not affect the time invested on each behavioral category, but prey taxon did. Moreover, although spiders used a similar strategy for capturing prey, they spent more time biting carabid larvae than other prey. Our results suggest that, at least in our study area, prey that are dangerous or the predator's size do not seem to affect Paratropis sp. acceptance per se, but can cause the predator to change the time budget allocated to each behavior.

Context Matters: Hawaiian Monk Seals Switch Between Feeding Strategies Depending on Ecological Context

The ability to expand the behavioral repertoire past seemingly rigid morphological features enables animals to succeed in a variety of ecological contexts. The integration of morphology, performance, and behavior produces diverse animal feeding strategies. These different strategies reflect trade-offs between specialization, prey choice, and energetic expenditure, which have important consequences for understanding individual and population-level flexibility in response to environmental change. Here we examined the feeding strategies used by the Hawaiian monk seal (Neomonachus schauinslandi), an endangered marine predator. We tested how Hawaiian monk seal feeding strategies change in response to ecological context, specifically prey size and prey location at different depths. Seven captive Hawaiian monk seals were fed five prey types across a continuum of sizes, and prey were presented at three depths to represent surface, pelagic, and benthic feeding. Hawaiian monk seals used suction feeding and biting strategies, and these strategies were associated with significant differences in behavior and kinematic performance. Hawaiian monk seals used suction feeding most frequently when targeting small to medium prey (0-79% of the seal's head length) but switched to biting when consuming large prey (>80% of the seal's head length). These results demonstrate that prey size drives the transition between suction feeding and biting strategies. Seals also switched strategies based on prey position in the water column, primarily using suction feeding when prey were benthic and pelagic, and biting when prey were at the water's surface. Overall, suction feeding was three to five times faster than biting, required a smaller gape, and used fewer jaw movements, allowing seals to quickly consume numerous small to medium sized prey. In contrast, biting was slower but resulted in the ability to target larger, potentially more energy rich prey. Our results show that Hawaiian monk seals exhibit flexibility in their use of different feeding strategies, which likely facilitates increased foraging success when feeding in spatially and temporally dynamic marine environments.

Shared extremes by ectotherms and endotherms: Body elongation in mustelids is associated with small size and reduced limbs

An elongate body with reduced or absent limbs has evolved independently in many ectothermic vertebrate lineages. While much effort has been spent examining the morphological pathways to elongation in these clades, quantitative investigations into the evolution of elongation in endothermic clades are lacking. We quantified body shape in 61 musteloid mammals (red panda, skunks, raccoons, and weasels) using the head-body elongation ratio. We also examined the morphological changes that may underlie the evolution toward more extreme body plans. We found that a mustelid clade comprised of the subfamilies Helictidinae, Guloninae, Ictonychinae, Mustelinae, and Lutrinae exhibited an evolutionary transition toward more elongate bodies. Furthermore, we discovered that elongation of the body is associated with the evolution of other key traits such as a reduction in body size and a reduction in forelimb length but not hindlimb length. This relationship between body elongation and forelimb length has not previously been quantitatively established for mammals but is consistent with trends exhibited by ectothermic vertebrates and suggests a common pattern of trait covariance associated with body shape evolution. This study provides the framework for documenting body shapes across a wider range of mammalian clades to better understand the morphological changes influencing shape disparity across all vertebrates.

Eat whole and less often: ontogenetic shift reveals size specialization on kelp bass by the California moray eel, Gymnothorax mordax

Despite the importance of predation in many ecosystems, gaps remain in our understanding of nocturnal marine predators. Although the kelp forests of Southern California are some of the most well-studied ecosystems, California morays, Gymnothorax mordax, are predominately nocturnal predators that have remained largely unstudied and their predatory effects on the kelp forest ecosystem are unknown. We use a multi-year data set to examine the dietary breadth of G. mordax and to determine the functional role of this predator. We also quantify bite force to examine the potential performance limitations of morays in exploiting prey. Stomach content analyses and linear selectivity index values indicate that G. mordax specializes on kelp bass, Paralabrax clathratus. Average size of kelp bass consumed varies across years, suggesting that morays respond to fluctuations in prey size availability. The scaling relationship of kelp bass standard length and moray head length reveals an ontogenetic shift, where maximum prey size increases with moray size and small prey are dropped from the diet of larger individuals. Moray bite force exhibited strong positive allometry with moray head size, suggesting that larger morays exhibit greater bite forces for their head and body size. However, we found no relationship between prey size and bite force, suggesting that a disproportional increase in bite force does not facilitate the consumption of disproportionately larger prey. Our results indicate that while G. mordax of Catalina Island is a dietary specialist, it is capable of exhibiting functional shifts in prey size and species based on their abundance.