Abstract:Livestock populations in protected areas are viewed negatively because of their interaction with native ungulates through direct competition for food resources. However, livestock and native prey can also interact indirectly through their shared predator. Indirect interactions between two prey species occur when one prey modifies either the functional or numerical responses of a shared predator. This interaction is often manifested as negative effects (apparent competition) on one or both prey species through … Show more
“…mobility, olfactory cues), as most probably exhibited here by wolf spider predators, is believed to be a more general precondition for alternative prey to result in positive indirect effects (e.g. Sabo & Power, ; Koss & Snyder, ; OwenâSmith & Mills, ; Sundararaj et al, ) and may explain the indirect effect that we observed.…”
Section: Discussionmentioning
confidence: 56%
“…Thus, if a predator eats two species with no preference for either prey, an increase in one species necessarily decreases predation rates on the second (Koss & Snyder, 2005). However, prey vary in their quality and one prey species may be more nutritious, easier to detect, capture, or handle (van Baalen et al, 2001;Sundararaj et al, 2012). For example, Finke and Denno (2003) found that visually hunting wolf spiders were more likely to capture easily detected mobile prey compared with more cryptic and sedentary prey.…”
1. Changes in one prey species' density can indirectly affect the abundance of another prey species if a shared predator eats both species. Sometimes, indirect effects occur when prey straddle habitats, including when riparian predator populations grow in response to emergent aquatic insects and increase predation on terrestrial prey. However, predators may largely switch to aquatic insects or become satiated, reducing predation on terrestrial prey.
2. To determine the net indirect effect of aquatic insects on terrestrial arthropods via generalist spider predators, a field experiment was conducted mimicking midge influx and a wolf spider numerical response inside enclosures near an Icelandic lake. Lab mesocosms were also used to assess per capita rates of spider predation u nder differing levels of midge abundance.
3. Midges always decreased sentinel prey predation, but this effect increased with predator density. When midges were absent, predation increased 30% at a high spider density, but predation was equal between spider treatments when midges were present. In situ arthropods showed no effect of midge or spider treatments, although nonâsignificant abundance patterns were observed congruent with sentinel prey results.
4. In lab mesocosms, prey survivorship increased â„50% where midges were present and rapidly saturated; the addition of 5, 20, 50, and 100 midges equivalently reduced spider predation, supporting predator distraction rather than satiation as the root cause.
5. The present results demonstrate a strong positive indirect effect of midges and broadly support the concept that predator responses to alternative prey are a major influence on the magnitude and direction of predatorâmediated indirect effects.
“…mobility, olfactory cues), as most probably exhibited here by wolf spider predators, is believed to be a more general precondition for alternative prey to result in positive indirect effects (e.g. Sabo & Power, ; Koss & Snyder, ; OwenâSmith & Mills, ; Sundararaj et al, ) and may explain the indirect effect that we observed.…”
Section: Discussionmentioning
confidence: 56%
“…Thus, if a predator eats two species with no preference for either prey, an increase in one species necessarily decreases predation rates on the second (Koss & Snyder, 2005). However, prey vary in their quality and one prey species may be more nutritious, easier to detect, capture, or handle (van Baalen et al, 2001;Sundararaj et al, 2012). For example, Finke and Denno (2003) found that visually hunting wolf spiders were more likely to capture easily detected mobile prey compared with more cryptic and sedentary prey.…”
1. Changes in one prey species' density can indirectly affect the abundance of another prey species if a shared predator eats both species. Sometimes, indirect effects occur when prey straddle habitats, including when riparian predator populations grow in response to emergent aquatic insects and increase predation on terrestrial prey. However, predators may largely switch to aquatic insects or become satiated, reducing predation on terrestrial prey.
2. To determine the net indirect effect of aquatic insects on terrestrial arthropods via generalist spider predators, a field experiment was conducted mimicking midge influx and a wolf spider numerical response inside enclosures near an Icelandic lake. Lab mesocosms were also used to assess per capita rates of spider predation u nder differing levels of midge abundance.
3. Midges always decreased sentinel prey predation, but this effect increased with predator density. When midges were absent, predation increased 30% at a high spider density, but predation was equal between spider treatments when midges were present. In situ arthropods showed no effect of midge or spider treatments, although nonâsignificant abundance patterns were observed congruent with sentinel prey results.
4. In lab mesocosms, prey survivorship increased â„50% where midges were present and rapidly saturated; the addition of 5, 20, 50, and 100 midges equivalently reduced spider predation, supporting predator distraction rather than satiation as the root cause.
5. The present results demonstrate a strong positive indirect effect of midges and broadly support the concept that predator responses to alternative prey are a major influence on the magnitude and direction of predatorâmediated indirect effects.
“…Numerical response is defined as the change in predator density as a function of prey density while functional response is the change in predator's intake rate as a function of prey density [30,31]. In the context of the conservation and management of large mammal populations, such indirect interactions have received little empirical investigation [32], let alone their policy implications. Figure 1.Schematic representation of apparent competition and apparent facilitation between livestock and wild prey, mediated by a predator.…”
An increasing proportion of the world's poor is rearing livestock today, and the global livestock population is growing. Livestock predation by large carnivores and their retaliatory killing is becoming an economic and conservation concern. A common recommendation for carnivore conservation and for reducing predation on livestock is to increase wild prey populations based on the assumption that the carnivores will consume this alternative food. Livestock predation, however, could either reduce or intensify with increases in wild prey depending on prey choice and trends in carnivore abundance. We show that the extent of livestock predation by the endangered snow leopard Panthera uncia intensifies with increases in the density of wild ungulate prey, and subsequently stabilizes. We found that snow leopard density, estimated at seven sites, was a positive linear function of the density of wild ungulatesâthe preferred preyâand showed no discernible relationship with livestock density. We also found that modelled livestock predation increased with livestock density. Our results suggest that snow leopard conservation would benefit from an increase in wild ungulates, but that would intensify the problem of livestock predation for pastoralists. The potential benefits of increased wild prey abundance in reducing livestock predation can be overwhelmed by a resultant increase in snow leopard populations. Snow leopard conservation efforts aimed at facilitating increases in wild prey must be accompanied by greater assistance for better livestock protection and offsetting the economic damage caused by carnivores.
“…Several studies have analyzed the functional response in simple predator-prey systems, from parasites and hosts (Morales et al 2001;Flores et al 2010) to vertebrate species such as nocturnal birds (Boutin 1995), feral cats (Harper 2005), Asiatic lions (Sundararaj et al 2012), lynxes, coyotes and wolves (Dale et al 1994;O'Donoghue et al 1998;Cariappa et al 2011). Systems with multiple prey species provide the opportunity for prey switching by generalist carnivores, but this has seldom been studied, unlike single prey systems, and data have previously been too limited for such an assessment for cougars [Puma concolor (Linnaeus, 1771)]; Ruth & Murphy 2010).…”
The study of predator-prey interactions is commonly analyzed using functional responses to gain an understanding of predation patterns and the impact they have on prey populations. Despite this, little is known about predator-prey systems with multiple prey species in sites near the equator. Here we studied the functional response of cougars (Puma concolor) in relation to their main prey, armadillo (Dasypus novemcinctus), coati (Nasua narica) and white-tailed deer (Odocoileus virginianus). Between 2004 and 2010, cougar scats were collected along 5 transects to estimate the consumption of different prey species. A relative abundance index (RAI) was calculated for each prey species and cougar using 18 camera traps. We compared Holling type I, II and III functional response models to determine patterns in prey consumption based on the relative abundance and biomass of each prey species consumed. The 3 main prey species comprised 55% (armadillo), 17% (coati) and 8% (white-tailed deer) of the diet. Type I and II functional responses described consumption of the 2 most common prey species armadillos and coati similarly well, while a type I response best characterized consumption of white-tailed deer. A negative correlation between the proportions of armadillo versus coati and white-tailed deer biomass in cougar scats suggests switching to consume alternative prey, confirming high foraging plasticity of this carnivore. This work represents one of the few studies to compare functional responses across multiple prey species, combined with evidence for prey-switching at low densities of preferred prey.
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