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Predation is a pervasive force that structures food webs and directly influences ecosystem functioning. The relative body sizes of predators and prey may be an important determinant of interaction strengths. However, studies quantifying the combined influence of intra‐ and interspecific variation in predator–prey body size ratios are lacking.We use a comparative functional response approach to examine interaction strengths between three size classes of invasive bluegill and largemouth bass toward three scaled size classes of their tilapia prey. We then quantify the influence of intra‐ and interspecific predator–prey body mass ratios on the scaling of attack rates and handling times.Type II functional responses were displayed by both predators across all predator and prey size classes. Largemouth bass consumed more than bluegill at small and intermediate predator size classes, while large predators of both species were more similar. Small prey were most vulnerable overall; however, differential attack rates among prey were emergent across predator sizes. For both bluegill and largemouth bass, small predators exhibited higher attack rates toward small and intermediate prey sizes, while larger predators exhibited greater attack rates toward large prey. Conversely, handling times increased with prey size, with small bluegill exhibiting particularly low feeding rates toward medium–large prey types. Attack rates for both predators peaked unimodally at intermediate predator–prey body mass ratios, while handling times generally shortened across increasing body mass ratios.We thus demonstrate effects of body size ratios on predator–prey interaction strengths between key fish species, with attack rates and handling times dependent on the relative sizes of predator–prey participants.Considerations for intra‐ and interspecific body size ratio effects are critical for predicting the strengths of interactions within ecosystems and may drive differential ecological impacts among invasive species as size ratios shift. [ABSTRACT FROM AUTHOR]

Predator diversity alterations have been observed in most ecosystems as a result of the loss and/ or addition of species. This has implications for predator-prey dynamics as non-trophic interactions among predators, so-called multiple predator effects ( MPE), are known to influence predation success. In addition, there is often a density-dependent relationship between prey availability and prey consumption (functional response). While MPE investigations are common in the literature, functional responses have rarely been incorporated into this field of predation ecology., Here, we outline an experimental procedure that incorporates functional responses into multiple predator effect studies. Using three fish species with different functional traits as model predators (bluegill Lepomis macrochirus, southern mouthbrooder Pseudocrenilabrus philander and banded tilapia Tilapia sparrmanii), we assess intra- and interspecific predator interaction outcomes on predator-prey dynamics. This was done by contrasting observed functional responses of heterospecific and conspecific combinations of predators with expected responses based on those of individual predators., Multipredator combinations produced variable results. Bluegill were the only species in which observed conspecific multipredator functional responses matched those of expected based on individual performance (prey risk neutral effects). In contrast, prey risk reduction was observed for both mouthbrooder and tilapia conspecific multipredator trials. Heterospecific combinations revealed strong prey risk reduction effects for mouthbrooder-tilapia and bluegill-tilapia trials, while mouthbrooder-bluegill multipredator functional responses combined additively. These results are discussed within the context of behavioural traits of the species and the development of a trait-based predictive framework., Using a functional response approach allowed for the assessment of multiple predator effects across a range of prey densities. We propose that the incorporation of within-guild predator combinations into classic functional response investigations will enhance predictive capacity development in competition and predation ecology., A is available for this article. [ABSTRACT FROM AUTHOR]

The post-parturition behavioural patterns of adult Xiphophorus helleri (Heckel) were described and quantified by recording their duration and/or frequency in glass tanks. All births occurred in the dark. Female behaviour might increase the chance of newborn juvenile survival: at the top of the tank, where juveniles are more vulnerable to predation, the females gave birth in the artificial refuge, while no parturition took place in the refuge at the bottom. Birth-giving females were no less cannibalistic than males and other females. There was a reduction in cannibalism and the frequency of secondary attacks with time, even though the number of juveniles in the tank continued to increase due to ongoing parturition. Most adults were found at the bottom of the water column during the first 500 min of parturition, after which they were distributed equally in the water column. The movement of adults, away from the bottom and consequently away from the juveniles corresponded with an increase in feeding on alternative food and a reduction in cannibalism. Thus, cannibalism in swordtail might be opportunistic predation. [ABSTRACT FROM AUTHOR]

The sabellid, Terebrasabella heterouncinata, is a small (<5 mm) intratubular brooder that lives in burrows within the host’s shell matrix. It is a semi-continuous breeder and despite producing small numbers of large eggs, infestation by this animal has reached epidemic proportions on local abalone farms. The present study compared the morphometrics and reproductive characteristics of worms from farmed and wild abalone, in the Walker Bay area of the south Western Cape Province of South Africa, to gain insights into why this animal has become so successful under aquaculture conditions. The farms designated farm A and farm B each had one “on-farm” site, and two wild sites, while farm C had two on-farm sites and two wild sites. The wild sites were natural abalone habitats located within 2.5 km of the farms. Our results conclusively showed that environmental conditions prevalent on the farms enhanced the reproductive success of these worms relative to that observed in its natural environment. At farms B and C, worms occurred in significantly higher densities at the on-farm sites than in the corresponding wild samples, but at farm A, density was equally low at the three sites. At all three farms, a greater proportion of the population was reproductively active in the on-farm samples than in the wild samples. Worms on farmed abalone had a higher instantaneous fecundity, brooded more clutches simultaneously and were larger than their conspecifics from the wild. There was a positive correlation between adult size and brood size and the number of clutches brooded simultaneously. Within the three on-farm sites there was a negative correlation between egg volume and brood size, indicating a trade-off between these traits. However, such a trade-off was not apparent between sites, with brood size being higher at the on-farm sites than at the wild sites, irrespective of egg size. This suggests that the stable nutrient-enriched environment on the farm led to an increase in fecundity without compromising the size (and implicitly the quality) of the eggs. Worm density did not have a significant effect on body size or any other reproductive traits at most sites, and the density of T. heterouncinata was unaffected by the density of other shell-infesting polychaetes. The results suggest that the farm environment has selected for larger, more fecund worms that breed rapidly with high recruitment success as a consequence of abundant nutrients, high host density, habitat stability and a possible lack of predation and interspecific competition. [ABSTRACT FROM AUTHOR]