A typical browser, the roe deer, may consume substantial quantities of grasses in open landscapes

In open landscapes, grass leaves provide an abundant resource for ruminants, with potentially high nutritional value. However, their extensive digestion requires a long fermentation time, achieved through large rumen and the stratification of the rumen content. Due to anatomical and physiological differences, ruminants differ in their ability to process grass leaves. Particularly, the small roe deer, with its viscous saliva and unstratified rumen content, is generally classified as a strict browser. We hypothesised that roe deer may be able to use grass leaves in some circumstances, notably when the availability of other resources declines and when the quality of grass leaves is high. We expected that (1) grass leave consumption should be higher in open landscapes than in forest habitat because grasses are more widely available and more nutritious in open landscapes and (2) grass leave consumption should increase in winter when the availability of other resources declines. We assessed grass consumption by microscopic analysis of roe deer faecal pellets collected monthly both in forest habitat and in the surrounding open landscape. We found that both the occurrence and the proportion of grass leaves in the faeces were higher in the open landscape (predicted mean proportion 0.31) than in the forest (predicted mean proportion 0.05). In addition, the proportion of grass leaves in the faeces was higher in winter and lower in spring in both forest and open landscape. We suggest that roe deer are able to use grass leaves with unusually high nutritional quality in winter in this mild climate area. This involves a certain level of digestive plasticity to efficiently digest high quality grasses and may confer nutritional benefit to individuals feeding in an open landscape.     

Habitat use under predation risk: hunting, roads and human dwellings influence the spatial behaviour of roe deer

Wildlife populations are subjected to increasing pressure linked to human activities, which introduce multiple stressors. Recently, in addition to direct effects, it has been shown that indirect (non-lethal) effects of predation risk are predominant in many populations. Predation risk is often structured in space and time, generating a heterogeneous “landscape of fear” within which animals can minimize risks by modifying their habitat use. Furthermore, for ungulates, resource quality seems to be positively correlated with human-related sources of risk. We studied the trade-off between access to resources of high-quality and risk-taking by contrasting habitat use of roe deer during daytime with that during nighttime for 94 roe deer in a hunted population. Our first hypothesis was that roe deer should avoid human disturbance by modifying their habitat use during daytime compared to nighttime. Our results supported this, as roe deer mainly used open fields during nighttime, but used more forested habitats during daytime, when human disturbance is higher. Moreover, we found that diel patterns in habitat use were influenced by hunting disturbance. Indeed, the roe deer decreased their use of high-crops during daytime, an important source of cover and food, during the hunting season. The proximity of roads and dwellings also affected habitat use, since roe deer used open fields during daytime to a greater extent when the distance to these sources of disturbance was higher. Hence, our results suggest that roe deer resolve the trade-off between the acquisition of high-quality resources and risk avoidance by modifying their habitat use between day and night.     

Diet quality and immunocompetence influence parasite load of roe deer in a fragmented landscape

The influence of landscape structure and host diet on parasite load of wildlife is still largely unknown. We studied a roe deer (Capreolus capreolus) population in a fragmented agricultural landscape in southern France to explore the relationship of gastrointestinal nematode load with spleen mass (to index immunocompetence), faecal nitrogen (to index diet quality), landscape structure and age of 33 hunt-harvested roe deer. Gastrointestinal worm counts were negatively related to faecal nitrogen and spleen mass, explaining respectively 24.7% and 9.2% of the observed variability in parasite load. Landscape structure did not appear to have a direct influence on gastrointestinal worm counts, but since animals from more open areas have a diet that is richer in nitrogen, its influence may be indirect. In conclusion, in the study area, the colonisation of the agricultural landscape does not seem to have increased the risk of gastrointestinal nematode parasitism for roe deer, possibly because access to high-quality food enhances immunocompetence.

     

Digestive plasticity as a response to woodland fragmentation in roe deer

Digestive plasticity, which refers to changes in digestive features due to changes in both internal and external environmental conditions, is a crucial factor for understanding the ability of species to cope with environmental changes. In Europe, agricultural intensification and the loss of forests have been major challenges for original forest dwellers, however some species, such as the European roe deer (Capreolus capreolus), have been able to successfully colonize these new habitats. In this work, we investigated the adaptation of some digestive features of roe deer to the agricultural landscapes. We assessed whether changes in local landscape structure influenced the mass of both reticulorumen (RR) and distal fermentation chamber (DFC) of 47 juvenile and adult roe deer inhabiting an agro-ecosystem in southwest France. Woodland cover had a clear effect on diet quality (estimated by the rate of gas production of digestive contents) and DFC weight of animals. In fact, deer from the most forested landscapes showed heavier DFCs and fed on poorer quality diet (lower gas production) than their counterparts from the most open landscapes. RR mass was less influenced by the landscape openness, being the age of animals the main factor for understanding the variations of this digestive feature in our study area. We can conclude that colonizing agricultural landscapes increases the access to highly energetic and digestive resources.     

Roe deer may markedly alter forest nitrogen and phosphorus budgets across Europe

Most forests in Europe are patchily distributed within the agricultural landscape. Therefore, forest biogeochemistry in Europe cannot be understood without considering the connectivity of nutrient cycles between forest patches and fertilized cropland. In this paper, we quantified the role of roe deer, the most widespread wild ungulate in Europe, as a vector of nitrogen and phosphorus from fertilized fields to forest patches, in a typical agricultural landscape of southwestern Europe. We derived a model of nutrient transfer from a data set on deer density, landscape‐use by individual deer, and nutrient content in feces. The model shows that the magnitude of nutrient transfer is highly sensitive to the proportion of forest patches within the landscape, and to the way deer use the landscape to feed and defecate. Hence, the magnitude of nutrient transfer varies substantially across the landscape. Locally, deer may significantly fertilize the forest, transferring the equivalent of almost 20% of the atmospheric deposition of nitrogen, and the equivalent of 0.13% of the total stock of phosphorus from cropland to forest patches each year. These inputs may markedly influence the biogeochemistry of forests in the long run, and the nitrogen to phosphorus ratio available to trees and forest plants. These results highlight the significant, but, heterogeneous, role of wild ungulates in forest biogeochemistry across Europe.     

Landscape fragmentation generates spatial variation of diet composition and quality in a generalist herbivore

Forest fragmentation may benefit generalist herbivores by increasing access to various substitutable food resources, with potential consequences for their population dynamics. We studied a European roe deer (Capreolus capreolus) population living in an agricultural mosaic of forest, woodlots, meadows and cultivated crops. We tested whether diet composition and quality varied spatially across the landscape using botanical analyses of rumen contents and chemical analyses of the plants consumed in relation to landscape metrics. In summer and non-mast winters, roe deer ate more cultivated seeds and less native forest browse with increasing availability of crops in the local landscape. This spatial variation resulted in contrasting diet quality, with more cell content and lower lignin and hemicellulose content (high quality) for individuals living in more open habitats. The pattern was less marked in the other seasons when diet composition, but not diet quality, was only weakly related to landscape structure. In mast autumns and winters, the consumption of acorns across the entire landscape resulted in a low level of differentiation in diet composition and quality. Our results reflect the ability of generalist species, such as roe deer, to adapt to the fragmentation of their forest habitat by exhibiting a plastic feeding behavior, enabling them to use supplementary resources available in the agricultural matrix. This flexibility confers nutritional advantages to individuals with access to cultivated fields when their native food resources are depleted or decline in quality (e.g. during non-mast years) and may explain local heterogeneities in individual phenotypic quality.     

Landscape fragmentation influences winter body mass of roe deer

Body size of large herbivores is a crucial life history variable influencing individual fitness‐related traits. While the importance of this parameter in determining temporal trends in population dynamics is well established, much less information is available on spatial variation in body size at a local infra‐population scale. The relatively recent increase in landscape fragmentation over the last century has lead to substantial spatial heterogeneity in habitat quality across much of the modern agricultural landscape. In this paper, we analyse variation in body mass and size of roe deer inhabiting a heterogeneous agricultural landscape characterised by a variable degree of woodland fragmentation. We predicted that body mass should vary in relation to the degree of access to cultivated meadows and crops providing high quality diet supplements. In support of our prediction, roe deer body mass increased along a gradient of habitat fragmentation, with the heaviest deer occurring in the most open sectors and the lightest in the strict forest environment. These spatial differences were particularly pronounced for juveniles, reaching >3 kg (ca 20% of total body mass) between the two extremes of this gradient, and likely have a marked impact on individual fates. We also found that levels of both nitrogen and phosphorous were higher in deer faecal samples in the more open sectors compared to the forest environment, suggesting that the spatial patterns in body mass could be linked to the availability of high quality feeding habitat provided by the cultivated agricultural plain. Finally, we found that adults in the forest sector were ca 1 kg lighter for a given body size than their counterparts in the more open sectors, suggesting that access to nutrient rich foods allowed deer to accumulate substantial fat reserves, which is unusual for roe deer, with likely knock‐on effects for demographic traits and, hence, population dynamics.