Predation & herbivory (article) | Ecology | Khan Academy
Adaptations of predators that help them catch prey, and adaptations of prey that begins to increase—due, at least in part, to low predation pressure—starting. a close relationship between the quality of food plants and small mammal cycles (e.g., Andersson and Jonasson , Sinclair et al. ), but it is still possible. The relationship between herbivores and plants is a cyclic cycle, fluctuating around . If there is a low predator density, then prey have less of a need to adapt.
Early work largely explored the trade-off in terms of prey behavioral and morphological plasticity Figure 1 747 Hence, prey are not unwitting victims. They behaviorally evade predators by becoming vigilant, shifting their foraging time budget, or shifting between foraging habitats and refuge habitats. Prey also induce anti-predator defense morphology, becoming cumbersome to handle by gape-limited predators, such as through the production of spines by zooplankton or through accelerated development by tadpoles to reach a predation size refuge.
Prey could also become better at evading predators such as by changing the development of musculature related to swimming 47 Predators in turn change their tactics to try to overcome prey defenses, setting up an eco-evolutionary game 16 More recent work shows that plastic responses of prey to perceived predation risk are fundamentally triggered by physiological stress Figure 1.
Physiological stress is an evolutionary conservative coping mechanism involving neuroendocrine responses that put prey in a heightened state of alertness and agility 2122 If chronic, predation-induced stress can cause prey to change their locomotor biomechanics to enhance escape performance Moreover, chronic stress can lead to chronically elevated metabolic rate 214951 — Whether or not prey become chronically stressed can depend on the hunting mode of their predator.
Sit-and-wait and sit-and-pursue predators may elicit persistent cues of their presence, triggering a heightened state of alertness and agility 54but a chronic stress response would be energetically wasteful when facing widely roaming predators where encounter frequency is low Elevated metabolism arising from perceived predation risk could change organismal nutrient demand and hence the kinds of resources consumed by prey 214951 — 53creating a physiological trade-off in nutrient allocation between maintenance respiration and both growth and reproduction which alters organismal fitness.
Thus, physiological plasticity to increase escape performance entails growth and reproductive costs, which can carry over to influence offspring performance through such things as maternal effects 224850but how those costs are borne depends on the capacity of individuals to exhibit adaptive behavior, which is reflected by within-population variation in the degree to which individuals can respond adaptively.
Classic approaches examining trait effects in communities have assumed that traits of an individual are fixed, such that differences in response among phenotypes are continuous and quantitative 234555 This leads to qualitative differences in the way individuals reconcile a trade-off between foraging gains and predator avoidance 44 For example, individuals in low food environments or in low energetic state or poor body condition may be motivated to play the trade-off game differently than individuals in high food environments or in high energetic state or high body condition.
Low-energetic-state individuals may accept greater predation risk because starvation risk outweighs predation risk. Alternatively, high-energetic-state individuals may opt to enhance their avoidance of predators 5758 because they can ride out pulses of risk or are protecting the body condition asset protection that they have already built up 59 — Hence, individuals may be perceived as being shyer or bolder depending on their nutritional or energetic state Predators may take advantage of these differences.
In spring, predatory barn owls hunt high-energetic-state gerbil prey prey with large energy storesgiving high energetic return for their foraging effort As summer progresses, high-energetic-state gerbils become more vigilant than low-energetic-state gerbils While owls still prefer high-energetic-state individuals, they increasingly hunt low-energetic-state individuals, thereby equalizing the hunting pressure on low- and high-energetic-state individuals Recent research shows that predator and prey personalities essentially amplify outcomes of general predator hunting mode—prey mobility interactions.
Personality becomes a key source of trait variation within populations. For example, northern pike predator—stickleback prey interactions involve personality-dependent reciprocal behavioral plasticity Pike orient and position themselves to strike moving sticklebacks. Sticklebacks in turn freeze in place to become cryptic to fend off an attack.
Pike orient longer before attacking when sticklebacks freeze, and the longer stickleback freeze the longer it takes before pike attack Hence, individuals that freeze longer shyer personalities tend to have higher survivorship, but that outcome is mediated by pike neurophysiology.
Individual pike with higher resting metabolic rates higher energy demands tend to be more aggressive and strike sooner than individuals with lower metabolic rates Predator aggressiveness then favors bolder stickleback individuals that freeze for shorter durations and move to escape.
Pike metabolic rate also determines hunting mode and habitat selection: More aggressive individuals also tend to have larger eyes for visual acuity Personality also determines contingent outcomes in interactions between black widow spider predators and cricket prey.
Bold crickets survive more poorly when facing bold spiders than when facing shy spiders, and vice versa Bold crickets seem to escape from spider webs long before shy spiders can subdue them but are quickly captured by bold spiders Shy crickets are less likely to move enough to encounter and be caught in webs Prey personality can influence outcomes with different predator species as well, as exemplified by interaction between mud crab prey that face active hunting blue crabs and sit-and-wait ambush toad fish Bold mud crabs are more likely to succumb to blue crabs because they spend more time outside of refuge habitats, whereas shy mud crabs spend more time in refuge habitats where toad fish tend to lie in wait These cases all illustrate how different personality types of predators can select for different prey personality types, preserving phenotypic diversity in both predator and prey populations Phenotypic diversity is also the basis for rapid evolutionary change 67 — 69which can lead to another form of state dependence—local adaptation of morphology, behavior, or physiology to environmental context A case in point is changes in biomechanical performance in an Anolis lizard species.
As a clade, arthropod-eating Anolis lizard species have adapted to occupy different habitat locations, including the ground, trunks of bushes, and branches. Body and limb morphology can discern which habitat is used.
Experimental introductions of a ground-dwelling predatory lizard onto small islands revealed that such differentiation in ecomorphology-habitat association could evolve within-species as well The introduced predator selected those individuals of a ground rock-dwelling ambush Anolis species that were poorly capable of climbing on trunks and branches This triggered plastic changes toward shorter limbs and longer digits of surviving Anolis to facilitate active maneuvering on thin branches and catching prey in the higher vegetation canopy.
Plasticity became an antecedent to locally adaptive evolutionary change in Anolis form and functional role within about 10—15 years, relative to those on control islands The interplay between plasticity and adaptive evolution is revealed further in a zooplankton, the water flea Daphnia, that has faced different predation regimes Daphnia produce eggs that often lie dormant in lake sediments.
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Generations of eggs, layered upon one another in the sediment, thus store key information about historical changes in environmental conditions within a lake. Laboratory experiments hatched Daphnia individuals from different sediment layers that represented periods before, during, and after fish presence. When the hatched individuals were exposed to fish cues, they expressed different degrees of plasticity and adaptation in vulnerability traits depending on if and when their parental populations were exposed to fish predators within their natal lakes Moreover, the degree of plasticity expressed by hatched individuals varied depending on the historical association with fish predators This again underscores the need to examine traits in action, including how different evolutionary processes drive the trait changes as environmental context changes in order to enhance predictive understanding of complexity underlying predator—prey dynamics and interactions.
The Anolis and Daphnia examples, as well as classic studies of Trinidadian guppies evolving different body morphology and coloration to cope with different predation regimes 70reveal that evolutionary processes can be quite rapid.
Evolutionary processes can operate contemporaneously with ecological processes, thereby creating eco-evolutionary feedbacks among environmental contexts 6771 — Rapid evolution in response to changing environmental contexts has been documented in a metapopulation of herbivorous stick insect species. In this system, local populations of the stick insect have heritable body coloration patterns that match local patches of their shrub host plants One shrub has lance-shaped leaves, and the other has ovoid leaves.
Individual stick insects are cryptic to bird predators on lance-leaved shrubs by expressing a dorsal stripe and are cryptic on ovoid-leaved shrubs by expressing a solid green color When patches of the different shrubs are in close proximity, gene flow between patches can cause maladaptation in local populations because of misaligned expression of insect body coloration in the shrub 38but more isolated populations exhibit local adaptation.
This preserves an eco-evolutionary process that creates a mosaic of stick insect ecotypes across a landscape Another recent case involves a lake-dwelling damselfly species.
Ancestral forms of the species evolved to coexist with predatory fish 74but this damselfly species has repeatedly invaded fishless lakes containing dragonfly predators. Heritability and selection studies revealed that the damselfly could evolve different predator coping mechanisms within 45 years Damselfly larvae in fish lakes evade predators by having low swimming propensity and slow swimming speeds, remaining motionless hence cryptic when facing predatory fish that can swim faster Damselfly larvae in dragonfly lakes instead swim faster to outrun their predators The rapid pace of human-caused environmental change such as habitat alteration or facilitation of species invasions has increased the likelihood that predator—prey interactions are occurring between species that have not coevolved.
Consequently, the traits of native predator and prey species may be poorly adapted for the conditions presented by the new species, whether it is a novel predator or a novel prey 75 The new encounters thus could change the relative importance of consumptive and non-consumptive effects that drive the eco-evolutionary game, raising concern about the loss of native predators and prey species and hence the need to manage invasives But here too the capacity for plasticity and rapid evolution may enable predator and prey species to cope with these new challenges and hence persist within the newly formed communities 7277 If this capacity is found to be widespread across predator and prey species, it could change our outlook on the fate of species in a rapidly changing world.
Conclusions There is growing appreciation that variety in the structure and functioning of ecological communities and ecosystems can be strongly dependent upon the evolutionary history of the interacting predator and prey species 67 — 7479 — If they become a target, they can try to fend off the attack with defences such as armour, quills, unpalatability or mobbing; and they can escape an attack in progress by startling the predator, shedding body parts such as tails, or simply fleeing.
They can also adopt behaviour that avoids predators by, for example, avoiding the times and places where predators forage. Camouflage and Mimicry Dead leaf mantis 's camouflage makes it less visible to both predators and prey. Syrphid hoverfly misdirects predators by mimicking a waspbut has no sting.
Prey animals make use of a variety of mechanisms including camouflage and mimicry to misdirect the visual sensory mechanisms of predators, enabling the prey to remain unrecognized for long enough to give it an opportunity to escape. Camouflage delays recognition through coloration, shape, and pattern. In mimicry, an organism has a similar appearance to another species, as in the drone flywhich resembles a bee yet has no sting.
It is lowest for those such as woodpeckers that excavate their own nests and progressively higher for those on the ground, in canopies and in shrubs. Birds also choose appropriate habitat e. Similarly, some mammals raise their young in dens. However, there are exceptions: For example, Belding's ground squirrel can distinguish several aerial and ground predators from each other and from harmless species.
Prey also distinguish between the calls of predators and non-predators.
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Some species can even distinguish between dangerous and harmless predators of the same species. In the northeastern Pacific Ocean, transient killer whales prey on seals, but the local killer whales only eat fish.
Seals rapidly exit the water if they hear calls between transients. Prey are also more vigilant if they smell predators. Population dynamics of predators and prey Populations of predators and prey in a community are not always constant over time. Instead, in many cases, they vary in cycles that appear to be related. The most frequently cited example of predator-prey dynamics is seen in the cycling of the lynx, a predator, and the snowshoe hare, its prey.
Strikingly, this cycling can be seen in nearly year-old data based on the number of animal pelts recovered by trappers in North American forests.
The number of hares fluctuates between 10, at the low points and 75, toat the high points. There are typically fewer lynxes than hares, but the trend in number of lynxes follows the number of hares.
The classic explanation is this: As hare numbers increase, there is more food available for the lynx, allowing the lynx population to increase as well. When the lynx population grows to a threshold level, however, it kills so many hares that the hare population begins to decline.
This is followed by a decline in the lynx population due to scarcity of food. When the lynx population is low, the hare population begins to increase—due, at least in part, to low predation pressure—starting the cycle anew.
Researchers demonstrate relationship between predation and extinction in small populations
Today, ecologists no longer think that the cycling of the two populations is entirely controlled by predation. For instance, it appears that availability of plant foods eaten by the hares—which decreases when hares become too abundant, due to competition—may also be a factor in the cycle.
Defense mechanisms against predation When we study a community, we must consider the evolutionary forces that have acted—and continue to act! Species are not static but, rather, change over generations and can adapt to their environment through natural selection.
Predator and prey species both have adaptations—beneficial features arising by natural selection—that help them perform better in their role.
For instance, prey species have defense adaptations that help them escape predation. These defenses may be mechanical, chemical, physical, or behavioral.
Mechanical defenses, such as the presence of thorns on plants or the hard shell on turtles, discourage animal predation and herbivory by causing physical pain to the predator or by physically preventing the predator from being able to eat the prey.
Chemical defenses are produced by many animals as well as plants, such as the foxglove, which is extremely toxic when eaten.