The effect of livestock on the physiological condition of roe deer (Capreolus capreolus) is modulated by habitat quality

Fernando Horcajada-Sánchez,Gema Escribano-Ávila,Carlos Lara-Romero,Emilio Virgós,Isabel Barja

doi:10.1038/s41598-019-52290-7

Abstract

Free-range livestock grazing is a widespread human activity that not only modifies natural vegetation but also leads to interactions with wild ungulates. Most commonly, the interactions between cattle and wild ungulates have been studied with a focus on competition for high-quality forage. However, other mechanisms, such as the risk of parasite infection, might better describe this interaction. We aim to determine whether livestock affect roe deer (Capreolus capreolus Linnaeus, 1758) by reducing habitat quality and increasing the probability of infection by shared parasites. We measured noninvasive fecal cortisol metabolites as an indicator of habitat quality as well as the lung nematode larvae burden from the Dictyocaulus genus. A higher Dictyocaulus larvae load was found in the presence of livestock in pines, and feces collected in winter had a higher parasite load than feces collected in autumn. Additionally, fecal cortisol metabolite levels in the roe deer were affected by the interaction between habitat quality and livestock presence and were higher in the poorest habitat and when living in sympatry with cattle. Our results suggest that physiological stress responses in roe deer were mediated by the habitat type and the presence of competitors. The long-term implications of altered physiological responses such as those demonstrated here should be considered in management strategies for deer.

Highlights

Habitat loss, fragmentation and degradation are among the main causes of the biodiversity crisis
To fully understand the relationships of livestock and wild ungulates living in sympatry, competition for food resources and other mechanisms such as parasite infection should be taken into account
The measurement of stress levels indexed by fecal cortisol metabolites (FCM) has been used in a range of studies to infer environmental factors that may harm fitness, including poor habitat quality or habitat degradation[13]

Summary

Introduction

Fragmentation and degradation are among the main causes of the biodiversity crisis. During winter and early spring (i.e., periods of reduced forage availability) in mountain areas, the effect of livestock grazing can be negative, as this is a period of higher starvation risk for wild ungulates[5] During these seasons, the diets of livestock and wild ungulates present a strong overlap[4] (and references therein), leading to food depletion for wild ungulates, which is a form habitat degradation. Prolonged exposure to stressors, such as reduced or poor forage quality, causes increased levels of glucocorticoids in the long term, which leads to ‘chronic stress’[17] Under these conditions, detrimental effects such as depressed immune responses, reduced reproductive success, suppressed growth, and decreased survival have been observed[15,16,17,18]. Detrimental, positive and neutral effects of stress levels on immune function have been found depending on genetic factors, social status and duration of stress[23] (for a review)

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