Interspecific competition between native Eurasian red squirrels and alien grey squirrels: does resource partitioning occur?

Abstract

In heterogeneous environments, differential niche selection by two competing species will result in niche partitioning so that individuals of each species can maximise their fitness under different sets of environmental variables. Thus, niche partitioning is considered essential to allow co-existence of ecologically related species. To assess whether niche partitioning was occurring between native red squirrels and alien grey squirrels living together in a 13-ha high-quality mixed deciduous woodland in north Italy, we investigated temporal and spatial patterns in their activity and foraging behaviour between 1996 and 1998. We used live trapping and radio-tracking to study numbers, distribution and behaviour of squirrels. Daily and seasonal temporal activity patterns, and activity on the ground and in the trees, were similar in the two species. However, grey squirrels were more tree specialists and had a narrower tree-species niche width than red squirrels, in particular making greater use of oak. Other studies of red and grey squirrels in allopatry show that the two species differ in the extent they utilise oak. Overall, tree-species niche overlap was about 70%. Grey squirrels had larger home ranges than red squirrels. Home ranges and core areas of both species were larger in males than females. Also, intraspecific home range and core-area overlap patterns were similar to those found in allopatric populations of these species. Overall, there was no evidence that the use of space of one species was affected by the other. Our results show that there was no niche partitioning of activity or foraging behaviour in time or space during the study. This suggests that, at moderate grey-squirrel densities, red squirrels are unable to avoid competition with grey squirrels, and that competition for food and/or space will occur when these resources become limiting

Dietary shifts in two vultures after the demise of supplementary feeding stations: consequences of the EU sanitary legislation

“…Coexistence of species exploiting the same resource is facilitated by heterogeneous environments, which allow differential use of patches with variable environmental features and resource availability (Brown et al 1994;Wauters et al 2002;Carrete et al 2005;Stephens et al 2007). Within those guilds embracing species having carnivore food habits, the diversity of the diet may be also based mainly on the variability in size of the prey (Begon et al 2006).…”

From daily movements to population distributions: weather affects competitive ability in a guild of soaring birds

“…Thus, variation in feeding morphology [2], activity pattern (e.g. diurnal versus nocturnal [3]), ability to dominate the resource [4] and habitat use [1], all have the potential to reduce competition between species and promote coexistence.…”

“…Consequently, the capacity for soaring flight is fundamental to the competitive ability of avian scavengers, making them a good model system with which to examine how environmental variation affects competitive ability. However, to date, environmentally invariant features, such as morphological adaptations for feeding have received much greater attention, with a range of studies showing that Old World vultures can be grouped into three consistent categories according to their skull dimensions and beak strength, which are associated with the parts and size of a carcass they target [2,5,14].…”

“…The expectation is that larger birds (with high wing loading) achieve higher crosscountry speeds when strong updraughts are available, thus providing them with a competitive advantage under these conditions. The study was undertaken in northwest Patagonia, where crested caracaras (Polyborus plancus), black vultures (Coragyps atratus) and Andean condors (Vultur gryphus) commonly aggregate at the same carcass, representing perhaps the world's largest range in body mass for sympatric soaring scavengers (ca 1.3-15 kg), although other systems have analogous scavenger assemblages [2,23]. While dominance at the carcass is usually correlated with body mass [6], with the Andean condor outcompeting all other species, black vultures are able to monopolize the carcass when they occur in sufficient numbers [24].…”

The use of species‐specific cone remains of sympatric arboreal rodents to monitor their distribution

“…(Council Directive 92/43/EEC). Finally, the Eurasian red squirrel, S. vulgaris Linnaeus, 1758, is being replaced in parts of its range, in the British Isles and areas in northern Italy, by the alien grey squirrel, S. carolinensis, a species introduced from North America that, in Europe, occupies a similar niche as the native congener (Gurnell & Pepper 1993;Lurz et al 2001;Wauters et al 2001Wauters et al , 2002aWauters et al , 2002bWauters et al , 2004. Recently the Finlayson's squirrel Callosciurus finlaysonii (Horsfield, 1824) has been found colonising an area along the Tyrrhenian coast in southern Italy (Aloise & Bertolino 2005;Amori & Aloise 2005).…”