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Murdoch, J. 2009. Competition and niche separation between corsac and red foxes in Mongolia. Doctor of Philosophy dissertation, University of Oxford, United Kingdom.
 
 

Abstract - Competition between species has the potential to profoundly affect the evolution of behaviour and the structure and dynamics of ecological communities.  Although the early studies of Lotka (1924), Volterra (1926), and Gause (1934, 1935) indicated that competition leads to exclusion under simple conditions, the prevalence of multiple, coexisting species occupying similar niches has been the focus of both theoretical and empirical studies over the last several decades.  While most competition studies have occurred under controlled conditions, those focusing on free-ranging carnivores remain relatively few, because most species are nocturnal, secretive, and range over large areas.  Yet, information on carnivore competition may be important for understanding interspecific relationships and developing conservation actions. 

I studied two wide-ranging carnivores, the corsac fox (Vulpes corsac) and red fox (V. vulpes), which occur sympatrically across northern and central Asia, to address the question of whether competition occurs between them and the extent to which niche partitioning may facilitate their coexistence.  Previous accounts suggested that both species occupy similar niches as they exhibit similar diets, activity patterns, and habitat selection.  However, few reliable details exist on the behaviour, ecology, and interspecific relations of either species in Asian biotopes, which may explain their coexistence over such a broad geographic area.  I conducted the study in the Ikh Nart Nature Reserve of Mongolia in a region that characterizes the arid environments of northern and central Asia.  I described and compared fox biotopes, and estimated survival and mortality of a radio-marked population to evaluate interference competition.  I also quantified and compared major niche axes between species, including their use of food, time, and habitat resources to examine niche separation and the potential for exploitation competition.

Foxes occurred sympatrically in Ikh Nart, occupying all major habitats, but corsacs occurred mainly in steppe areas, whereas red foxes occurred mainly in semi-desert areas.  Survival rates were similar between species and mortality resulted mostly from human hunting, but also predation by larger canids – red foxes caused 30% of corsac mortality, and grey wolves (Canis lupus) and dogs accounted for 25% of red fox mortality – and rarely from unknown causes.  Both foxes exhibited similar diets that included mainly insects and rodents, but also birds, reptiles, carrion, vegetation, fruit and seeds, and garbage.  Despite relatively high overlap in foods consumed, dietary differences were apparent during most of the year, but not during the winter months, when food abundance was lowest.  Foxes displayed similar patterns of activity, with both species being primarily nocturnal, but occasionally active during crepuscular and daytime hours.  Activity did not differ across 24-hour periods, but during nighttime, differences in hourly movement rates were evident.  Corsac and red foxes occupied home ranges that varied little in size and habitat composition throughout the year.  Red fox home ranges averaged 12.9 km2 and were approximately twice as large as those of corsacs, which averaged 6.5 km2.  Foxes used habitats differently at multiple spatial scales, with corsacs selecting steppe habitats in open plains like closed shrubland, semi-shrubland, and tall grassland, and red foxes selecting more rugged, semi-desert habitats like rocky outcrops, open shrubland, and open forbland. 

The results suggest that competition occurs between corsac and red foxes, and that niche separation along all three axes contributes to their coexistence.  The conditions required for competition, including niche overlap and resource limitation, were apparent.  The greatest evidence for competition included multiple instances red foxes killing corsacs, which strongly suggests that interference competition regularly occurs.  Exploitation competition also appeared to occur at some level, but was probably reduced by significant, fine-scale partitioning of food, time, and habitat resources.  Some morphological differentiation may further contribute to coexistence, as red foxes captured during the study were heavier and larger than corsacs.

The study provides among the first quantitative details of corsac and red fox biology in Asia, as well as insight into the nature of competition and coexistence between wide-ranging carnivores.  The study also provides information that may be directly applied to the conservation of corsac and red foxes, both of which have experienced declines in Mongolia.  The study provided a baseline measure of the biological requirements of foxes useful for conservation planning, and revealed that Ikh Nart’s game ranger program was ineffective at reducing fox mortality from poaching.  Specific recommendations include targeting ranger patrols on Siberian marmot (Marmota sibirica) colonies and extending the reserve and its core protected zone to include greater proportions of steppe habitats and rocky outcrops.  I also recommend modifying the current management regime, which focuses on argali sheep (Ovis ammon) as an umbrella species, to include multiple species.

 

Publisher - University of Oxford, Wildlife Conservation Research Unit (WildCRU)

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