Relative influence of inter- and intra-specific competition in an ungulate assemblage modified by introductions

Valentina Zini, Kristin Waeber, Paul M. Dolman

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Inter-specific competition from introduced and naturally-colonising species has potential to affect resident populations, but demographic consequences for vertebrates have rarely been tested. We tested hypotheses of inter- and intra-specific competition for density, body mass and fertility of adult female roe deer Capreolus capreolus across a heterogeneous forest (195 km 2 ) landscape also occupied by introduced Mediterranean fallow deer Dama dama and sub-tropical muntjac Muntiacus reevesi. Species-specific deer densities in buffers around culling locations of 492 adult female roe deer (sampled over seven years 2011-2017), were extracted from spatially-explicit Density Surface Models calibrated through extensive annual nocturnal thermal imaging distance sampling. Roe deer fertility and body mass were related to local species-specific deer 23 densities and local extent of arable lands (that provides nutritious food) using Piecewise Structural Equation Models. Muntjac density (mean=15.1 SD=7.6) was lower at higher fallow deer densities (inter-quartile effect size, IQ=-2.4, suggesting inter-specific avoidance (interference), but was greater when buffers included more arable (IQ=+1.01 Roe deer body mass (13.7kg, SD=1.52) was marginally greater when buffers included more arable (IQ=0.32kg) and was independent of deer densities. However, roe deer fertility was unrelated to body mass, suggesting fertility benefits of condition exceeded an asymptotic threshold in this low-density population. Consistent with this, roe deer fertility was slightly greater (not reduced) in areas with greater local roe deer density (IQ=+0.9% probability of two instead of one or zero embryos), again indicating negligible intra-specific competition. In contrast, roe deer were less fertile in areas with greater muntjac densities (IQ=-14%), thus inter-specific exceeded intra-specific competition in this assemblage. In contrast, we found no support for any effects of fallow deer density on roe deer density, body mass or fertility. Complex networks of inter-specific competition operate in this deer assemblage. For muntjac, interspecific interference from fallow deer exceeded habitat effects. For native roe deer, inter-specific competition from introduced, smaller sedentary muntjac reduced fertility, unlike intra-specific or potential competition with larger, more mobile, fallow deer. Mechanisms may include behavioural interference or stress; resource depletion is considered less likely as roe deer fertility was independent of body mass. Findings emphasise the importance of ensuring appropriate management strategies for controlling invasive species.
Original languageEnglish
JournalJournal of Mammalogy
Early online date31 Mar 2023
Publication statusE-pub ahead of print - 31 Mar 2023


  • feral deer
  • interference competition
  • intra-specific competitionn
  • invasion biology
  • invsive species
  • inter-specific competition

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