Non-preferred Prey Research Articles

Prey selection and time to consumption differ between congeneric muskellunge and northern pike

Understanding whether fishes feed selectively is important for informing conservation and management actions such as selecting receiving waters for stocked fishes and prioritizing nursery habitats for preservation or restoration. We conducted a laboratory experiment to determine if (1) age-0 muskellunge (Esox masquinongy) and northern pike (E. lucius), two primarily piscivorous congeners in the Laurentian Great Lakes, fed selectively among four prey species (bluntnose minnow [Pimephales notatus], johnny darter [Etheostoma nigrum], rock bass [Ambloplites rupestris], and yellow perch [Perca flavescens]) with different anti-predator behaviors and morphologies, and (2) prey selection and time to consumption differed between predators. Muskellunge strongly selected bluntnose minnow and avoided the other prey species. Northern pike also strongly selected bluntnose minnow and avoided johnny darter and rock bass, but exhibited slight avoidance to neutral selection of yellow perch. Mean time to consumption differed between species, with northern pike feeding more quickly than muskellunge. Further controlled experimentation is needed to reveal whether growth and survival differs when these predators consume preferred vs. non-preferred prey. In the interim, we recommend managers presume nursery habitats with soft-rayed, fusiform, non-demersal prey fishes are most likely to support growth and survival of age-0 muskellunge and northern pike.

Opportunistic feeding by lions: non-preferred prey comprise an important part of lion diets in a habitat where preferred prey are abundant

Optimal foraging theory predicts less diverse predator diets with a greater availability of preferred prey. This narrow diet niche should then be dominated by preferred prey, with implications for predator–prey dynamics and prey population ecology. We investigated lion (Panthera leo) diets in Hluhluwe–iMfolozi Park (HiP), South Africa, to assess whether lions in a site with a high density of preferred prey (prey species weighing 92–632 kg as estimated from a published meta-analysis) have a narrow diet, consisting primarily of preferred prey. HiP is a useful study site to investigate this prediction because it is a productive landscape (with a high density of prey) where lion-preferred prey constitutes up to 33% of the prey available to lions. Furthermore, to investigate whether lions in HiP exhibit sex-specific diets as documented in other southern African populations, we estimated male and female lion diets separately. We were specifically interested in testing whether traditional approaches of estimating lion diets at the population level mask sex-specific predation patterns, with possible implications for management of lions in small to medium-sized fenced reserves. Lions in HiP preferred larger prey species (63–684 kg) and had diets with a larger proportion of preferred prey than reported in an African-wide meta-analysis. However, despite the high density of preferred prey species, 36% of lion diets still consisted of typically non-preferred species such as nyala (Tragelaphus angasii). This finding suggests that lions in HiP maintain a degree of opportunism even when preferred prey are abundant. Therefore, abundant, non-preferred prey are likely to be an important resource for lion populations. Sex-specific differences in lion diets were evident in HiP, suggesting that estimation of lion resource use and carrying capacity should consider opportunistic hunting and sex-specific differences in lion diets.

Prey diversity effects on ecosystem functioning depend on consumer identity and prey composition.

Consumer diversity effects on ecosystem functioning are highly context dependent and are determined by consumer specialization and other consumer and prey specific traits such as growth and grazing rates. Despite complex reciprocal interactions between consumers and their prey, few experimental studies have focused on prey diversity effects on consumer dynamics and trophic transfer. In microbial microcosms, we investigated effects of algal prey diversity (one, two and four species) on the production, evenness and grazing rates of 4 ciliate consumers, differing in grazing preferences and rates. Prey diversity increased prey biovolume in the absence of consumers and had opposing effects on different consumers, depending on their specialization and their preferred prey. Consumers profited from prey mixtures compared to monocultures of non-preferred prey, but responded negatively if preferred prey species were offered together with other species. Prey diversity increased consumer evenness by preventing dominance of specific consumers, demonstrating that the loss of prey species may have cascading effects resulting in reduced consumer diversity. Our study emphasizes that not only the degree of specialization but also the selectivity for certain prey species within the dietary niche may alter the consequences of changing prey diversity in a food web context.

Dietary shift in juvenile coral trout (Plectropomus maculatus) following coral reef degradation from a flood plume disturbance

Acute environmental disturbances impact on habitat quality and resource availability, which can reverberate through trophic levels and become apparent in species' dietary composition. In this study, we observed a distinct dietary shift of newly settled and juvenile coral trout (Plectropomus maculatus) following severe coral reef habitat degradation after a river flood plume affected the Keppel Islands, Australia. Hard coral cover declined by similar to 28 % in the 2 yr following the 2010-2011 floods, as did the abundance of young coral trout. Gut contents analysis revealed that diets had shifted from largely crustacean-based to non-preferred prey fishes following the disturbances. These results suggest that newly settled and juvenile coral trout modify their diet and foraging strategy in response to coral habitat degradation. This bottom-up effect of habitat degradation on the diet of a top coral reef predator may incur a metabolic cost, with subsequent effects on growth and survival.

Diet–demography relationships in a long‐lived predator: from territories to populations

Understanding the mechanisms that shape animal population dynamics is of fundamental interest in ecology, evolution and conservation biology. Food supply is an important limiting factor in most animal populations and may have demographic consequences. Optimal foraging theory predicts greater consumption of preferred prey and less diet diversity when food is abundant, which may benefit key fitness parameters such as productivity and survival. Nevertheless, the correspondence between individual resource use and demographic processes in populations of avian predators inhabiting large geographic areas remains largely unexplored, particularly in complex ecosystems such as those of the Mediterranean basin. Based on a long‐term monitoring program of the diet and demography of Bonelli's eagleAquila fasciatain western Europe, here we test the hypothesis that a predator's diet is correlated to its breeding productivity and survival at both the territorial and population levels, and ultimately to its population growth rate. At the territorial level, we found that productivity increased with greater consumption of European rabbitsOryctolagus cuniculus, the Bonelli's eagle's preferred prey, and pigeons, an important alternative prey for this predator. The survival of territorial pairs was negatively affected by higher diet diversity, which probably reflected the inability to find sufficient high quality prey. Diet effects at the population level were similar but more noticeable than at the territorial level, i.e. a greater consumption of rabbits, together with lesser consumption of small‐to‐medium avian species (‘other birds’; non‐preferred prey), increased productivity, while greater diet diversity and lower consumption of rabbits was associated with reduced survival and population growth rate. Overall, our study illustrates how the diet of a predator species can be closely related to key individual vital rates, which, in turn, leave a measurable fingerprint on population dynamics within and among populations across large spatial scales.

Determining the relative importance of dilution and detection for zebra foraging in mixed-species herds

For many animals, a key benefit of group living is lowered predation risk. With increasing group size, individuals commonly reduce vigilance. This group size effect can arise from both dilution of risk and increased collective detection. To determine which was more important, we compared vigilance levels of plains zebra, Equus quagga, in areas inhabited by their main predator, lion, Panthera leo, as a function of herd size and composition (zebra-only versus mixed-species herds). For zebra-only herds, vigilance declined with increasing zebra numbers. In contrast, in mixed-species herds, zebra vigilance levels were significantly lower and did not vary with the total number of ungulates and/or zebra in the herd. This lower vigilance can be explained by detection benefits, since we controlled for the influence of herd size (i.e. dilution) statistically. Furthermore, we found that zebra in smaller herds were half as vigilant when they co-occurred with another preferred prey of lion, blue wildebeest, Connochaetes taurinus, compared with zebra-only herds. However, when zebra foraged with impala, Aepyceros melampus, a nonpreferred prey, there was only a slight reduction in vigilance compared with similar-sized zebra-only herds. Interestingly, the decrease in zebra vigilance when herding with wildebeest was influenced by the presence/absence, but not number, of wildebeest. In contrast, impala only reduced zebra vigilance when they comprised about 75% of the herd. Ultimately, our results indicate that for zebra in mixed-species herds, detection benefits are relatively more important than dilution over a larger range of herd sizes. However, detection only reduces vigilance when zebras herd with species that share a common predator (i.e. diluting partner). Potentially, detection by species that do not share a common predator (i.e. low-diluting partner) is not as reliable as detection by diluting species.

Innate pattern recognition and categorization in a jumping spider.

The East African jumping spider Evarcha culicivora feeds indirectly on vertebrate blood by preferentially preying upon blood-fed Anopheles mosquitoes, the vectors of human malaria1, using the distinct resting posture and engorged abdomen characteristic of these specific prey as key elements for their recognition. To understand perceptual categorization of objects by these spiders, we investigated their predatory behavior toward different digital stimuli - abstract ‘stick figure’ representations of Anopheles constructed solely by known key identification elements, disarranged versions of these, as well as non-prey items and detailed images of alternative prey. We hypothesized that the abstract images representing Anopheles would be perceived as potential prey, and would be preferred to those of non-preferred prey. Spiders perceived the abstract stick figures of Anopheles specifically as their preferred prey, attacking them significantly more often than non-preferred prey, even when the comprising elements of the Anopheles stick figures were disarranged and disconnected from each other. However, if the relative angles between the elements of the disconnected stick figures of Anopheles were altered, the otherwise identical set of elements was no longer perceived as prey. These data show that E. culicivora is capable of making discriminations based on abstract concepts, such as the hypothetical angle formed by discontinuous elements. It is this inter-element angle rather than resting posture that is important for correct identification of Anopheles. Our results provide a glimpse of the underlying processes of object recognition in animals with minute brains, and suggest that these spiders use a local processing approach for object recognition, rather than a holistic or global approach. This study provides an excellent basis for a comparative analysis on feature extraction and detection by animals as diverse as bees and mammals.

Scarcity in the prey community yields anti-predator benefits

The majority of individuals in a community belong to a small number of abundant species. Understanding why some species are rare and others are common has been a long-held goal for ecologists. Africa’s large carnivore guild preferentially preys on a small number of species within a limited weight range. Within this weight range however, some species that are expected to be significantly preferred as prey are not. I tested whether these species avoid preferential predation through their low densities. Records of over 40,000 kills from up to 48 different communities were used to test if non-preferred species within the expected prey weight ranges of each large predator avoid preferential predation and why. Species expected to be prey of Africa’s large predators based on their body mass, that are preferred are preyed upon significantly more frequently at low densities than non-preferred prey. This results in a negative relationship between relative abundance and preference for preferred prey, but a positive relationship for non-preferred prey. The non-preferred prey species that are within the expected prey weight ranges of Africa’s large predators are significantly less abundant within the prey community than significantly preferred prey. Rarity in African ungulates may convey an anti-predator benefit in that it was suboptimal for predators to evolve morphological or behavioral strategies to optimally forage on them or in that prey species can avoid predators by existing in habitats with low carrying capacity.

Early exposure to odors changes later visual prey preferences in cuttlefish

Developmental studies have shown that environmental stimulation received by a developing sensory system can alter the developmental outcome of both that sensory system and other aspects of the nervous system. We investigated the ecologically relevant question of whether prior exposure to prey early in development within one sensory modality could influence later prey choice within a different sensory modality. Cuttlefish are visual predators; they can detect prey odors but attacks on prey cannot be elicited without visual stimulation. Cuttlefish eggs were exposed to the odor of shrimp (preferred prey), crabs (non-preferred prey), mollusks (non-prey), or a seawater control (no prey). Seven days after hatching, prey preferences were tested with a visual choice test between crabs and shrimp. Hatchlings exposed to crabs odors and the seawater control were significantly more likely to attack shrimp. Hatchlings exposed to mollusk odors showed no visual prey preference, while those exposed to shrimp preferentially attacked crabs. These results demonstrate a complex relationship between an early sensory exposure and later prey preference

Does artificial selection for fixed prey preference affect learning in a predatory mite? Experiments to unravel mechanisms underlying polyphagy in Hypoaspis aculeifer

Individual reproductive success in polyphagous arthropod predators critically depends on the prey species included in their diet. Hence, selection will act on traits that enable the predator to tune its preference to the best prey available. Such traits may be either rigid or flexible and are manifested as genetically fixed or learned preferences. Whether these two types of behaviour are mutually exclusive or manifest themselves in condition-dependent ways, is still an open question. We sought possible answers by studying a soil-dwelling predatory mite (Hypoaspis (Gaeolaelaps) aculeifer Canestrini), known to exhibit a genetic polymorphism in prey preferences within local populations. We had previously shown that 4 generations of artificial selection on the choice for either of two astigmatic mites (Rhizoglyphus robini and Tyrophagus putrescentiae) resulted in isofemale lines with contrasting prey preferences (<I>R</I>-line and <I>T</I>-line) and that the preference traits are inherited as though they are monogenic without dominance. In this article, we ask whether artificial selection has influenced the ability to switch preferences in a condition-dependent way. First, we conditioned the female predators of both isofemale lines by starving them in the presence of odour from each of the two prey species separately or in the absence of any prey odour. Then, at least half an hour later, we assessed their prey preference in two-choice tests. When starved in presence of odour from non-preferred prey, both lines show a slight but non-significant increase in preference for their preferred prey. However, when starved in presence of odour from the preferred prey, predators of both lines showed a clear and significant switch toward the alternative prey. This shows the ability of predatory mites to memorize the odour experienced during starvation, and to change their prey preference. It also shows that - despite four generations of artificial selection for a fixed prey preference - they retain the ability to exhibit a form of learning and to switch preferences. This result sheds new light on the impact of selection on fixed and flexible prey preferences in polyphagous arthropod predators that experience different dominant prey species in space and time.

Trade-offs associated with dietary specialization in corallivorous butterflyfishes (Chaetodontidae: Chaetodon)

Increasing dietary specialization is an inherently risky strategy because it increases a species’ vulnerability to resource depletion. However, risks associated with dietary specialization may be offset by increased performance when feeding on preferred prey. Although rarely demonstrated, highly specialized species are expected to outperform generalists when feeding on their preferred prey, whereas generalists are predicted to have more similar performance across a range of different prey. To test this theory, we compared the growth rates of two obligate coral-feeding butterflyfishes (Chaetodon trifascialis and Chaetodon plebeius) maintained on exclusive diets of preferred vs nonpreferred prey. In the field, C. trifascialis was the most specialized species, feeding almost exclusively on just one coral species, Acropora hyacinthus. C. plebeius meanwhile, was much less specialized, but fed predominantly on Pocillopora damicornis. During growth experiments, C. trifascialis grew fastest when feeding on A. hyacinthus and did not grow at all when feeding on less preferred prey (P. damicornis and Porites cylindrica). C. plebeius performed equally well on both A. hyacinthus and P. damicornis (its preferred prey), but performed poorly when feeding on P. cylindrica. Both butterflyfishes select coral species that maximize juvenile growth, but contrary to expectations, the more specialized species (C. trifascialis) did not outperform the generalist species (C. plebeius) when both consumed their preferred prey. Increased dietary specialization, therefore, appears to be a questionable strategy, as there was no evidence of any increased benefits to offset increases in susceptibility to disturbance.

Early familiarization overrides innate prey preference in newly hatched Sepia officinalis cuttlefish

In the cuttlefish Sepia officinalis, hatchlings do not benefit from parental care and have to search independently for their own food. We investigated the effect of exposing newly hatched cuttlefish to a nonpreferred prey on their subsequent choice of prey. We tested the choice of food between crabs (nonpreferred) and shrimps (preferred) made by 3-day-old cuttlefish that had been exposed visually and chemically to crabs at hatching, or had been exposed visually only to crabs, or had had no exposure to crabs. Juveniles that had been exposed to crabs significantly preferred crabs, whereas hatchlings that had had no crab exposure preferred shrimps. These results show that a simple visual exposure to a naturally nonpreferred prey immediately on hatching is sufficient to change the juvenile cuttlefish's innate preference.

Effect of early feeding experience on subsequent prey preference by cuttlefish, Sepia officinalis

Food preferences were investigated in cuttlefish during the first 3 months' posthatching, using choice tests between crabs, shrimps, and young fish. The results showed that without previous feeding experience, cuttlefish preferred shrimps on Day 3. This suggests an innate food preference; however, it was possible to induce a preference for an originally nonpreferred prey item in 3-day-old and naïve cuttlefish, demonstrating the flexibility of this initial behavioral preference in response to previous individual experience. This preference suggests a learning process involving a form of long-term memory, demonstrated for the first time in juvenile cuttlefish. Until Day 30, juvenile cuttlefish fed exclusively shrimps chose shrimps. This preference probably depends on their previous feeding experience. Finally, it appears that from Day 60, cuttlefish reared on the same restricted diet have a tendency to switch their preference to novel prey items, which diversify their diet.

Rapid taste aversion learning in adult cuttlefish, Sepia officinalis

The common cuttlefish is an opportunistic predator with certain prey preferences. The literature suggests that learning plays a role in the predatory behaviour of cuttlefish. However, nothing is known about taste aversion learning in cephalopods. We developed a learning procedure in which the preferred prey of the experimental cuttlefish was made distasteful by a bitter taste (quinine). In the training session, the modified prey was repeatedly presented until the experimental cuttlefish stopped attacking it. Of 32 experimental cuttlefish, 26 attacked a different prey from the originally preferred one when both were presented in a choice test 24 or 72 h after learning. In contrast, matched control cuttlefish that had not been subjected to negative reinforcement continued to choose the initially preferred prey under identical test conditions. These results are the first demonstration of taste aversion learning in cephalopods. They underline essential adaptive functions in cuttlefish and the flexibility of their feeding behaviour. Cuttlefish were able to learn that a prey is not acceptable food, even if they usually preyed on it, to recognize it and to avoid it for several days and as a result to eat a usually nonpreferred prey.

Experimental predation by sticklebacks on larval mackerel and protection of fish larvae by Zooplankton alternative prey

Three-spined sticklebacks Gasterosteus aculeatus L. strongly prefer larvae of Atlantic mackerel Scomber scombrus L. over smaller wild invertebrate Zooplankton in experiments where the sticklebacks were allowed to feed ad libitum and to voluntary cessation. The relative preference for fish larvae increased as their proportion declined, a “counter-switching” behavior. In spite of this increasing preference, the presence of Zooplankton as alternative prey strongly protected the fish larvae from predation. This occurred because at high plankton abundance (or low ratio of fish larvae to zooplankton) the total number of fish larvae (and total biomass) ingested by the sticklebacks during their voluntarily limited foraging periods decreased, despite lack of satiation. The mechanism for this interaction appears to be interference by the zooplankton (nonpreferred prey) in the stickleback's search for fish larvae. We interpret the stickleback's response (cessation of feeding before satiation) as equivalent to control of total ingestion by mean prey size, which would have the effect of maximizing the rate of food intake while minimizing foraging time. This result and the counter-switching are consistent with adaptations for minimizing risk from its own predators while foraging.

Coral Reef Recovery on Guam (Micronesia) After Catastrophic Predation by Acanthaster Planci.

At Tanguisson Reef, Guam, in 1968-1969 a population explosion of the coral-eating sea star Acanthaster planci devastated the coral community. In the wake of this predation, coral species richness, density, and cover were drastically reduced, and the species composition was altered. In two of three reef zones examined, < 1% coral cover remained. At the time of disturbance, some considered the magnitude of this and similar Acanthaster disturbances unprecedented, and predicted long recovery times because reefs were viewed as mature, stable communities. This major disturbance offered an opportunity to study the processes and rate of community recovery. Using the data from previous studies in 1970, 1971, and 1974, and my data from 1980-1981, I present a long-term analysis of coral community development. I have focused on coral recruitment, survivorship, and species settlement patterns in relationship to the remnant surviving population. The preference of Acanthaster planci for certain prey (e.g., Montipora and Acropora) shifted the species composition to one in which nonpreferred prey predominated (e.g., Porites and Leptastrea). The predominance of nonpreferred prey was short-lived, and by 1980, preferred prey were the primary colonists of two zones. The three biological zones (reef front, submarine terrace, and seaward slope) had their own characteristic species assemblages soon after the disturbance. Nonrandom recruitment or survival of juvenile corals (diameter ≤ 4 cm) established these zones. Although the percentage of juvenile corals fell throughout the survey, their highest density was reached after adult colonies were established. In 1980, of the 34 species examined, 79% showed a significant coefficient of association between adult and juvenile conspecifics. This association caused clumped species dispersion patterns to develop within zones. As the result of recruitment, species diversity rose from 84 species in 1970 to 154 species in 1981. As surviving corals and new recruits developed, the distribution of coral growth forms became more diversified. There was a drastic increase in coral cover (e.g., submarine terrace zone, 0.9% in 1970 to 65% in 1981). This increase in cover corresponded to an increase in size and number of the coral colonies In 12 yr, species richness, cover, and composition reached or exceeded measurements of comparable reefs before the disturbance. The recovery occurred faster than predicted by a stable equilibrium model because long-term successional changes were not required. Recovery was accelerated because Acanthaster did not destroy the structural integrity of reef framework. This rapid recovery from a natural disturbance demonstrates that some coral communities have a greater resilience than was once believed.

Predation by the epipelagic heteropod mollusk Carinaria cristata forma japonica

In surface waters off Southern California (USA), Carinaria cristata forma japonica van der Spoel, 1972 feeds on a variety of zooplankton, although thaliaceans, chaetognaths, and copepods predominate numerically in the diet. Feeding intensity is greatest on the most abundant of two species of thaliaceans, depending on which one dominates in the plankton at the time. Some cannibalism occurs, with the prey being about one half the size of the predator. Feeding intensity is greatest during the day, possibly because heteropods depend on vision to locate prey and because prey species are more available by day. Comparisons of the proportion of each prey species in the diet and in the plankton indicate preferential feeding on thaliaceans, chaetognaths, and mollusks; in contrast, crustaceans and especially the copepods are non-preferred prey. These preference patterns may reflect differences among prey species in the ability to escape capture. Predator and prey size are positively correlated for Doliolum denticulatum gonozoids and oozoids, Thalia democratica aggregates, and Sagitta spp. Smaller individuals of D. denticulatum gonozoids and Sagitta spp. are selectively preyed on, resulting in size refuges for larger individuals.

Preferential Feeding: An Optimization Strategy in Sea Urchins

Strongylocentrotus drobachiensis and S. franciscanus exhibited strong algal preferences in laboratory studies. A generalized ranking of algae from most to least preferred for both sea urchins includes: Nereocystis luetkeana, Costaria costata, Laminaria saccharina, L. groenlandica, Monostroma fuscum, Opuntiella californica, Agarum fimbriatum and A. cribrosum. Similar but weaker preferences were exhibited by S. purpuratus. Preference experiments showed that substance(s) readily sloughed from the fronds of Nereocystis attract urchins whereas substances from A. fimbriatum repel or are not detected by urchins. In the field urchins in contact with or on the fronds of Agarum spp. revealed a low proportion of feeding individuals except during winter. Food preferences were inversely correlated with the caloric content of algae. Although preferences generally were weakly correlated with caloric intake, this relationship is an artifact of the high feeding rates on preferred algae. Absorption efficiencies for the thr...