You can run--or you can hide: optimal strategies for cryptic prey against pursuit predators

We consider the optimal behavior of a cryptic prey individualas it is approached by a predator searching for prey. Althoughthe predator has not yet discovered the prey, it has an increasinglikelihood of doing so as it gets closer to the prey. Further,the closer the predator is to the prey when it discovers it,the more likely the predator will be to capture the prey. Thesearguments suggest that the prey should flee before the predatordiscovers it. However, the act of fleeing will alert the predatorto the presence of the prey and trigger an attack that mightnot have occurred otherwise. We capture these conflicting outcomesin a mathematical model, which we then use to predict the optimalbehavior of the prey and predator. We argue that the optimalstrategy for the prey is either to run as soon as they detecta predator approaching or to only flee in response to havingbeen detected by the predator. Running as soon as the predatoris detected is associated with low predator search speeds, alow nonpredation cost to running, a large advantage to the preyin initiating chases rather than reacting, limited ability tospot the predator at distance, a high ability to spot prey bythe predator, and a high probability that chases will be successful.The optimal strategy for the predator depends on whether itscurrent trajectory is taking it closer to or further from theprey. In the latter case, the predator should attack immediatelyon discovering the prey; in the former case, it should delayits attack until it reaches the point on its current trajectorywhere distance to the prey is minimized.     

Prey classification by an araneophagic ant-like jumping spider (Araneae: Salticidae)

What to attack is one of the most basic decisions predators must make, and these decisions are reliant upon the predator's sensory and cognitive capacity. Active choice of spiders as preferred prey, or araneophagy, has evolved in several distantly related spider families, including jumping spiders (Salticidae), but has never been demonstrated in ant-like jumping spiders. We used prey-choice tests with motionless lures to investigate prey-choice behaviour in Myrmarachne melanotarsa , an East African ant-like salticid that normally lives in aggregations and often associates with other spider species. We show that M . melanotarsa chooses spiders as prey in preference to insects and, furthermore, discriminates between different types of spiders. Myrmarachne melanotarsa 's preferred prey were juvenile hersiliids and its second most preferred were other salticids. To date, all documented examples of araneophagic salticids have been from the basal subfamily Spartaeinae. Myrmarachne melanotarsa is the first non-spartaeine and also the first ant-like salticid for which araneophagy has been demonstrated.     

Better to be bimodal: the interaction of color and odor on learning and memory

Defended prey frequently advertise to potential predators usingmultimodal warning displays. Signaling through more than onesensory pathway may enhance the rate of avoidance learning andthe memorability of these learned avoidances. If this is so,then mimetic insects would gain more protection from mimickinga multimodal rather than a monomodal model. Day-old domesticchicks (Gallus gallus domesticus) were used to examine whethera common insect warning odor (pyrazine) enhanced learning andmemorability of yellow prey, a common warning color. Pyrazineincreased the rate at which the chicks learned to avoid unpalatableyellow prey, and how well this learned avoidance was rememberedafter a 96-h interval. After 96 h, mimics of the multimodalprey were avoided, whereas mimics of the monomodal prey werenot. In the absence of pyrazine, chicks generalized their learnedavoidance of the unpalatable yellow prey to palatable greenprey; however, the presence of pyrazine reduced this color generalization.These results suggest that much is to be gained from signalingmultimodally, for both models and mimetic prey species. Thepresence of multimodal prey in the habitat may also advantagethe predators as it allows it them to distinguish more easilybetween palatable and unpalatable prey.     

不同猎物及密度对巴氏新小绥螨和拉戈钝绥螨同类相残和集团内捕食作用的影响

明确不同猎物及密度下巴氏新小绥螨Neoseiulus barkeri与拉戈钝绥螨Amblyseius largoensis(Muma)的同类相残和集团内捕食作用,为其协同应用控制橡胶树害螨提供依据.在室温27±1℃、湿度75％±5％、光周期12 L∶12D 条件下,以六点始叶螨 Eotetranvchus sexmac...     

Intraguild Predation among the Hoverfly Episyrphus balteatus de Geer (Diptera: Syrphidae) and Other Aphidophagous Predators

Aphidophagous predators compete for the same prey species. During their foraging activity they frequently encounter heterospecific aphid predators. These situations can lead to intraguild predation and may disrupt biological control efforts against aphids where more than one predator species is present. We investigated the behavior of larvae of the hoverfly Episyrphus balteatus de Geer and its interaction with three other aphid predators: the ladybird Coccinella septempunctata L., the lacewing Chrysoperla carnea Stephens, and the gall midge Aphidoletes aphidimyza (Rondani). Interspecific interactions between predators were examined in arenas of different sizes and in the presence of extraguild prey. The outcome of interactions between E. balteatus larvae and the other predators depended predominantly on the relative body size of the competitors. Relatively large individuals acted as intraguild predators, while relatively smaller individuals became intraguild prey. Eggs and first- as well as second-instar larvae of E. balteatus were highly susceptible to predation by all other predators, whereas pupae of E. balteatus were preyed upon only by the larvae of C. carnea. Interactions between A. aphidimyza and E. balteatus were asymmetric and always favored the latter. Eggs and first- as well as second-instar larvae of E. balteatus sustained intraguild predation irrespective of the size of the arena or the presence of extraguild prey. However, the frequency of predation on third-instar larvae of E. balteatus was significantly reduced. This study indicated that the same species can be both intraguild predator and intraguild prey. It is suggested that combinations of predators must be carefully chosen for success in biological control of aphids.     

Prey preferences of the spotted hyaena (Crocuta crocuta) and degree of dietary overlap with the lion (Panthera leo)

Spotted hyaenas Crocuta crocuta were once considered mere scavengers; however, detailed research revealed that they are very efficient predators. Information on what spotted hyaenas actually prefer to prey on and what they avoid is lacking, as well as the factors that influence prey selection. Data from 14 published and one unpublished study from six countries throughout the distribution of the spotted hyaena were used to determine which prey species were preferred and which were avoided using Jacobs' index. The mean of these values for each species was used as the dependent variable in multiple regression, with prey abundance and prey body mass as predictive variables. In stark contrast to the rest of Africa's large predator guild, spotted hyaenas do not preferentially prey on any species. Also surprisingly, only buffalo, giraffe and plains zebra are significantly avoided. Spotted hyaena most prefer prey within a body mass range of 56–182 kg, with a mode of 102 kg. The dietary niche breadth of the spotted hyaena is similar to that of the lion Panthera leo , and the two species have a 58.6% actual prey species overlap and a 68.8% preferred prey species overlap. These results highlight the flexible and unselective nature of spotted hyaena predation and are probably a reason for the species' success throughout its range, despite a large degree of dietary overlap with lions.     

Do non‐native fish as prey favour the conservation of the threatened indigenous Eurasian otter?

1. Biological invasions are considered a major threat to biodiversity. Most research has focused on the distribution, biology and impacts of non‐native species on native fauna and flora. However, few studies have explored their role as prey for native predators of conservation concern. 2. To assess the incidence and intensity of predation by the Eurasian otter Lutra lutra on established non‐native fish species, data were collated from the published literature. To be selected, studies had to cover at least 1 year, analyse more than 100 spraints and report the study period and percentage relative frequency (%RF) of all prey fish species. 3. To permit reliable, time‐related comparisons with %RF of non‐native fishes in otter diet, we also reviewed available information about both the distribution of non‐native fishes and history of their introductions to European countries, revealing a decrease with longitude in the number of naturalised non‐native fishes taken (ranging between 5 and 34) and their percentage in each fish assemblage. 4. Our selective criteria were met by 30 dietary studies from 44 study areas in 15 European countries during 1970–2010. The extent to which otters rely on non‐native fishes was almost negligible (mean %RF = 4.8), with the number of non‐native fishes preyed upon by otters decreasing with both latitude and longitude. 5. The %RF of non‐native fish in the diet increased slightly with time, with otters preying significantly more on non‐native fish in study areas where alterations of the fish assemblage had been highlighted in the reference papers. No relationship was found between otter diet breadth and the occurrence of non‐native fishes in their diet. 6. The current role of non‐native species in otter diet suggests that effective otter conservation management plans should focus on the maintenance and/or enhancement of native fish assemblages.     

Does predator abundance influence species diversity of equilibrium macroinvertebrate assemblages in spring fens?

1. Predation may significantly control number and density of coexisting species. The effects of predation on species diversity have traditionally been tested in experiments and theoretical models of simple trophic systems. In complex natural ecosystems, however, disentangling multiple sources of variation is difficult. In groundwater-fed environments, a significant effect of predation can be expected due to the relatively stable environmental conditions; however, it has never been properly examined.
2. We analysed species diversity and total abundance of macroinvertebrate assemblages in 48 Western Carpathian spring fens, separately for whole sites and mesohabitat/season, and partitioned the effects of predation intensity from those of environmental variables in robust models using a bootstrapping technique. We verified our results by accounting for taxa resistant to predation.
3. The assumption that predation-mediated coexistence of species is the main mechanism responsible for the relatively species-rich assemblages in the Western Carpathian spring fens was not supported. However, predation may significantly influence abundance of non-predatory species and, under some conditions, it may contribute to explaining patterns in species diversity.
4. The effect of predation did not differ between the mesohabitats with different stability. However, we found higher environmental control in spring and a stronger effect of predators in autumn, which suggests that different mechanisms influence fen assemblages in different seasons.
5. Our study provides a new robust approach how to test the effect of predation on natural macroinvertebrate assemblages. The importance of predation was lower than expected in equilibrium assemblages but it may vary in time.