Les hommes ont oublié cette vérité. Mais tu ne dois pas l'oublier, dit le renard. Tu deviens responsable pour toujours de ce que tu as apprivoisé.
Le Petit Prince, chap. 21

Saturday, 9 February 2013

Intraguild interactions between dogs and wild carnivores

Vanak, A.T. 2008. Intraguild interactions between native and domestic carnivores in Central India. PhD. University of Missoury

I determined the various factors affecting the resource selection and spatial ecology of the Indian fox Vulpes bengalensis, a small canid endemic to the Indian subcontinent. Despite being widespread throughout India, and commonly occurring in many dry grassland habitats, little is known about the ecology of this species. I investigated habitat selection by the Indian fox in a grassland region in central India that represents a mix of natural and human-dominated habitats to discern if and how foxes respond to human encroachment on native habitats. I collected home range and habitat selection data on 32 radio-collared Indian foxes in the Great Indian Bustard Wildlife Sanctuary, Nannaj, Maharashtra over a one year period. Adult Indian fox 95% kernel density home-range sizes varied between sexes and among seasons. Males had consistently larger home-ranges than females across all seasons but there was no interseasonal variation. Females had smaller home-range sizes during the cool-dry season which is also the denning period, than during any other season. Compositional analysis of Indian fox selection of home-ranges at the landscape level showed heavy influence of the presence of grasslands, plantations and fallow land. Indian foxes avoided humanmodified habitat such as agricultural land and human settlements. The presence of grasslands was also the dominant predictor of Indian fox habitat selection across seasons within the home-range as determined by AIC ranked discrete-choice models. The results indicate that Indian foxes select for natural grasslands and avoid human-modified habitat.
The distribution, abundance and resource selection patterns of meso-carnivores such as the Indian fox are also heavily influenced by the effects of top-down intraguild competition with sympatric larger carnivores. Competitive dynamics among carnivores are asymmetric and interference competition and the associated occurrence of intraguild predation are unidirectional, with larger carnivores negatively influencing smaller carnivores. Competition can affect the subordinate competitor in several ways: by limiting spatial distributions resulting in scattered interspecies territories, constraining habitat selection, reducing prey encounter rates and food intake, or requiring increased hunting effort.
In my study area, the domestic dog Canis familiaris, is the most common midsized carnivore. As the world’s most common carnivore, dogs are known to interact with wildlife as predators, prey, competitors, and disease reservoirs or vectors. Despite these varied roles in the community, the interaction of dogs with sympatric carnivores is not well understood. Dogs have the potential to be exploitative, interference and apparent competitors with sympatric carnivores.
I examined competition for food between dogs and the Indian fox through dietary analysis. Dogs subsisted largely on human derived material from direct feeding, and scavenging on garbage, crop residue and livestock carcasses (83% relative occurrence).

Wild caught foods constituted only 11% relative occurrence of dog diet. Indian foxes are omnivorous and included a wide variety of food types in their diet. The majority of  Indian fox diet consisted of invertebrates (33% relative occurrence), rodents (20% relative occurrence) and fruits of Zizyphus mauritiana (18.5% relative occurrence). Indian foxes did not include any human derived material, nor did they scavenge from large mammal carcasses, and included only a small portion of agricultural produce in their diet. The diet of free-ranging dogs is typical of dogs from other parts of the world. However, the low contribution of human-derived food sources to the diet of Indian foxes was surprising since the species is a generalist carnivore. Although there was limited dietary overlap between dogs and foxes in this study, dogs may actually be preventing foxes from accessing agricultural lands and human associated foods by interference competition.

Dogs have the potential to be effective interference competitors, especially with medium and small-sized carnivores, and may fulfill the role of a mid-sized canid, especially in areas where the native large carnivore community is depauperate. I experimentally examined the behavioral responses of the Indian fox to the presence of dogs and dog odors. Since resource competition between dogs and foxes is low, it is unclear whether foxes perceive dogs as interference competitors. To test this I exposed foxes to neutral, live dog, and animal odor cues at food trays and recorded the amount of food eaten, time spent at food trays, and vigilance and non-vigilance behaviors. When dogs were visible, foxes continued to visit the food trays, but reduced the amount of time spent (by 83%) and food eaten (by 70%) at those trays. Foxes were 10 times more vigilant during dog trials than during neutral and odor trials and also exhibited lower levels of non-vigilance behavior (resting, playing) when dogs were visible. In contrast, dog odors did not affect fox foraging and activity. These results show that vigilance/foraging tradeoffs due to interference competition can occur between native and domestic carnivores, despite low dietary overlap.

To avoid the effects of interference competition and intraguild predation, subordinate competitors such as the Indian fox can alter space use patterns which may result in a reduction of foraging opportunities. To determine if interference competition between dogs and foxes influences the space use patterns of foxes at a landscape level, I conducted a radio-telemetry study of 32 Indian foxes and 25 free-ranging dogs in and around the Great Indian Bustard Wildlife Sanctuary in central India. Using a logistic regression analysis in an information theoretic framework, I determined the effects of landcover type, primary prey abundance (rodents) and dog presence on the landscape on the space use of foxes. As expected, Indian foxes showed low overlap with dogs based on the volume of intersection index. Top AIC ranked models showed a positive influence of grasslands and a negative influence of agricultural land and dog presence. Rodent abundance only had a weak positive effect. This suggests that fox space use is determined not only by habitat type, but also influenced by the presence of a mid-sized carnivore, the dog.

These results suggest that the competitive intraguild dynamics that are seen among wild carnivores can also occur between wild and domestic carnivores, despite a seeming lack of competition for food and other resources. The role of dogs as intraguild competitors of wild carnivores has thus far been under-recognized. Dogs are among the world’s most common carnivores and are heavily subsidized by humans. As a result, they can occur at high densities even in rural areas, where they tend to range freely into wild habitats. Therefore, dogs can pose threats to native carnivore communities, and extend the edge of anthropogenic disturbance well beyond the borders of human settlements.

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