The competitor release effect applied to carnivore species: how red foxes can increase in numbers when persecuted

The objective of our study was to numerically simulate the population dynamics of a hypothetical community of three species of small to medium–sized carnivores subjected to non–selective control within the context of the competitor release effect (CRE). We applied the CRE to three carnivore species, linking interspecific competition with predator control efforts. We predicted the population response of European badger, the red fox and the pine marten to this wildlife management tool by means of numerical simulations. The theoretical responses differed depending on the intrinsic rate of growth (r), although modulated by the competition coefficients. The red fox, showing the highest r value, can increase its populations despite predator control efforts if control intensity is moderate. Populations of the other two species, however, decreased with control efforts, even reaching extinction. Three additional theoretical predictions were obtained. The conclusions from the simulations were: 1) predator control can play a role in altering the carnivore communities; 2) red fox numbers can increase due to control; and 3) predator control programs should evaluate the potential of unintended effects on ecosystems.

Colonization of abandoned land by Juniperus thurifera is mediated by the interaction of a diverse dispersal assemblage and environmental heterogeneity

Land abandonment is one of the most powerful global change drivers in developed countries where recent rural exodus has been the norm. Abandonment of traditional land use practices has permitted the colonization of these areas by shrub and tree species. For fleshy fruited species the colonization of new areas is determined by the dispersal assemblage composition and abundance. In this study we showed how the relative contribution to the dispersal process by each animal species is modulated by the environmental heterogeneity and ecosystem structure. This complex interaction caused differential patterns on the seed dispersal in both, landscape patches in which the process of colonization is acting nowadays and mature woodlands of Juniperus thurifera, a relict tree distributed in the western Mediterranean Basin. Thrushes (Turdus spp) and carnivores (red fox and stone marten) dispersed a high amount of seeds while rabbits and sheeps only a tiny fraction. Thrushes dispersed a significant amount of seeds in new colonization areas, however they were limited by the presence of high perches with big crop size. While carnivores dispersed seeds to all studied habitats, even in those patches where no trees of J. thurifera were present, turning out to be critical for primary colonization. The presence of Pinus and Quercus was related to a reduced consumption of J. thurifera seeds while the presence of fleshy fruited shrubs was related with higher content of J. thurifera seeds in dispersers' faeces. Therefore environmental heterogeneity and ecosystem structure had a great influence on dispersers feeding behaviour, and should be considered in order to accurately describe the role of seed dispersal in ecological process, such as regeneration and colonization. J. thurifera expansion is not seed limited thanks to its diverse dispersal community, hence the conservation of all dispersers in an ecosystem enhance ecosystems services and resilience.

Non-invasive monitoring of adrenocortical activity in European badgers (Meles meles) and effects of sample collection and storage on faecal cortisol metabolite concentrations

Due to the increasing demand for methods to quantify adrenal activity in response to stressors in wild animals, we evaluated whether stimulation with adrenocorticopic hormone (ACTH) increases faecal cortisol metabolite levels in European badgers. We also conducted several experiments to evaluate the effect of storage time and collection methods on cortisol metabolite levels of faecal samples. Faecal samples were collected from five captive European badgers (Meles meles) and cortisol metabolites were quantified by an enzyme immunoassay. Faecal cortisol metabolite levels increased 1-2 days after ACTH injection and dropped to pre-treatment levels 3 days after ACTH stimulation. We found that cortisol metabolite levels were not affected by the 8-hour time lapse from collection in the field until freezing of faecal samples, environmental exposure (temperature 25.66 ± 2.55°C; range 21.20-32.20) or mean relative humidity 62.77 ± 9.90% (range 42.00-79.00). Cortisol metabolites were not homogenously distributed in the scats. Cortisol metabolite levels were significantly lower when faecal extracts and samples were frozen for long periods of time (14 weeks or more). Thus, the measurement of faecal cortisol metabolites is a suitable method for the non-invasive evaluation of adrenocortical activity in European badgers. However, some aspects related to the collection and storage of faecal samples should be considered in future studies conducted with this species.

Predator-prey relationships in a Mediterranean vertebrate system: Bonelli's eagles, rabbits and partridges

How predators impact on prey population dynamics is still an unsolved issue for most wild predator-prey communities. When considering vertebrates, important concerns constrain a comprehensive understanding of the functioning of predator-prey relationships worldwide; e.g. studies simultaneously quantifying 'functional' and 'numerical responses' (i.e., the 'total response') are rare. The functional, the numerical, and the resulting total response (i.e., how the predator per capita intake, the population of predators and the total of prey eaten by the total predators vary with prey densities) are fundamental as they reveal the predator's ability to regulate prey population dynamics. Here, we used a multi-spatio-temporal scale approach to simultaneously explore the functional and numerical responses of a territorial predator (Bonelli's eagle Hieraaetus fasciatus) to its two main prey species (the rabbit Oryctolagus cuniculus and the red-legged partridge Alectoris rufa) during the breeding period in a Mediterranean system of south Spain. Bonelli's eagle responded functionally, but not numerically, to rabbit/partridge density changes. Type II, non-regulatory, functional responses (typical of specialist predators) offered the best fitting models for both prey. In the absence of a numerical response, Bonelli's eagle role as a regulating factor of rabbit and partridge populations seems to be weak in our study area. Simple (prey density-dependent) functional response models may well describe the short-term variation in a territorial predator's consumption rate in complex ecosystems.

Laying the foundations for a human-predator conflict solution: assessing the impact of Bonelli's eagle on rabbits and partridges

Background

Predation may potentially lead to negative effects on both prey (directly via predators) and predators (indirectly via human persecution). Predation pressure studies are, therefore, of major interest in the fields of theoretical knowledge and conservation of prey or predator species, with wide ramifications and profound implications in human-wildlife conflicts. However, detailed works on this issue in highly valuable –in conservation terms– Mediterranean ecosystems are virtually absent. This paper explores the predator-hunting conflict by examining a paradigmatic, Mediterranean-wide (endangered) predator-two prey (small game) system.

Methodology/Principal Findings

We estimated the predation impact (‘kill rate’ and ‘predation rate’, i.e., number of prey and proportion of the prey population eaten, respectively) of Bonelli's eagle Aquila fasciata on rabbit Oryctolagus cuniculus and red-legged partridge Alectoris rufa populations in two seasons (the eagle's breeding and non-breeding periods, 100 days each) in SE Spain. The mean estimated kill rate by the seven eagle reproductive units in the study area was c. 304 rabbits and c. 262 partridges in the breeding season, and c. 237 rabbits and c. 121 partridges in the non-breeding period. This resulted in very low predation rates (range: 0.3–2.5%) for both prey and seasons.

Conclusions/Significance

The potential role of Bonelli's eagles as a limiting factor for rabbits and partridges at the population scale was very poor. The conflict between game profitability and conservation interest of either prey or predators is apparently very localised, and eagles, quarry species and game interests seem compatible in most of the study area. Currently, both the persecution and negative perception of Bonelli's eagle (the ‘partridge-eating eagle’ in Spanish) have a null theoretical basis in most of this area.

The presence of a “competitor pit effect” compromises wild rabbit (Orcytolagus cuniculus) conservation

Abstract

Wild rabbit (Oryctolagus cuniculus) populations have suffered a dramatic reduction over the last 30 years in Spain. Rabbit decline has been recurrently associated with several epizootics and habitat changes. The role of interspecific competition has been usually neglected. This study analyzes the effects of habitat suitability and wild boar (Sus scrofa) occurrence, a hypothetical predator and competitor species, on a small and isolated population of rabbits. To test this effect we used a GLM with the abundance of rabbits as response variable and wild boar occurrence as predictor. To avoid habitat confounding effects we included vegetation structure variables and elevation summarized in PCA factors. Rabbits showed a very restricted and aggregated distribution and a very low abundance across the study area. In contrast, wild boar was present in all sampled plots but one and showed moderatehigh abundance. The three best models included both wild boar occurrence and principal component factor 2. Rabbits were located in opened Mediterranean areas where trees were small and scarce, rock cover was low and wild boar occurrence was also low. Nowadays wild boar populations are not directly controlled in private lands and its hunting is forbidden in National Parks in Spain. Waiting for further research to evaluate the threshold of rabbit densities below which competitors and/or predators may prevent the recovery of rabbit populations, control of wild boars may be useful as a short-term strategy to recover small rabbit populations whenever it is linked to habitat improvements.

Spatial distribution models in a frugivorous carnivore, the stone marten (Martes foina): is the fleshy-fruit availability a useful predictor?

Abstract

Fleshy-fruit availability is rarely used as a predictor in stone marten (Martes foina) habitat models, despite its frugivorous carnivore diet. Data on stone marten occurrence, habitat structure and fleshy-fruit species abundance was collected along 2 km long survey routes within 2 × 2 km sample plots (n = 30). Two different spatial scales were considered: 1) the entire survey route; and 2) 200 m segments within each 2 km survey route. Data analyses included Poisson General Linear Models (GLM) and Generalized Linear Mixed Models (GLMM) for the first and second approaches, respectively.Strawberry tree (Arbutus unedo) availability was significantly and positively correlated to stone marten occurrence at both spatial scales, particularly for the large-scale model. At the larger scale, a lower correlation to the traditional habitat structure variables was observed. Tree cover was the most important variable in the small-scale model, but strawberry tree availability was also an important predictor. Stone marten abundance was low in areas of high tree cover and absence of strawberry trees; emphasising the prominent role of strawberry trees per se in the abundance of stone martens. Our results indicated that including fine, field-derived estimates of key food resources for species can increase the utility of habitat models.

Predictive niche modelling to identify potential areas of conflicts between human activities and expanding predator populations: a case study of game management and the grey mongoose, Herpestes ichneumon, in Spain

Context. The grey mongoose, Herpestes ichneumon L., is a protected species in Spain. Populations of grey mongoose are currently increasing in numbers, and potential conflicts with human interests involving predation of small-game species, may arise in the near future. Aims. We predicted potential suitable areas for the expansion of grey mongoose by using a niche modelling approach to detect areas of conflict with small-game hunting activities. Methods. We compared these areas with regions in which small-game hunting is an important economic activity. To produce a niche-suitability map we used Maxent and an internal (data-splitting) validation to assess the predictive performance of the model. Areas in which small-game hunting is important were identified by using a rabbit-abundance index. Key results. On the basis of suitability modelling, populations of grey mongoose will expand into southern and central Spain. The variables with higher predictive power are mainly climatic, although some mosaic habitat types are also important. Internal validation reveals a strong correspondence between predicted and observed records. The overlap of high-suitability areas with areas assigned with a high rabbit-abundance index indicated the existence of large regions of potential conflict with hunting interests. Conclusions. Predictions of niche modelling can be used to detect conflict areas between expanding species and human interests. As a consequence of the expansion of the grey mongoose, the incidence of non-selective predator control may increase, thereby posing a threat to other protected predators. Implications. Identified areas of likely conflict should be prioritised to delineate careful management programs in terms of people education, surveying, incentives and the detection of illegal predator-control activities.

Wolf response to two kinds of barriers in an agricultural habitat in Spain

We examined the effect of two kinds of barriers on an expanding gray wolf, Canis lupus L., 1758, population in an agricultural habitat in north-central Spain. The barriers were (i) a four-lane fenced highway along a flat area without wildlife-crossing facilities, and (ii) the River Duero Artery (RDA), comprising the river itself (50–100 m wide) and several small infrastructures along it. From March 1997 to October 2001, all 4 radio-collared wolves living <15 km from the highway (1 adult territorial male, 1 territorial breeder female, 1 dispersing male, and 1 female in 3 periods of her life (territorial immature, disperser, and territorial breeder) crossed it on between 4% and 33% of 45–163 monitoring days via vehicle bridges. Moreover, 4 more highways that we monitored in areas without radio-collared wolves have not delayed expansion of the increasing wolf population, suggesting that these highways are not an important barrier for wolves in our study area. In contrast, only 3 of 8 wolves radio-collared <5 km from the RDA were detected crossing it, and 2 of those 3 started to cross it only after severe habitat disturbance; in addition, the RDA seems to have delayed wolf expansion for some 15 years, which suggests that it is a semipermeable barrier for wolves. We discuss the likely consequences of the RDA on the recovery of the Iberian wolf population.

Spatial variation in helminth community structure in the red-legged partridge (Alectoris rufaL.): effects of definitive host density

Parasite community ecology has recently focused on understanding the forces structuring these communities. There are few surveys, however, designed to study the spatial repeatability and predictability of parasite communities at the local scale in one host. The purpose of our study was to address the relationship between infracommunity and component community richness, and to describe spatial variations on the local scale, of helminth parasite communities in an avian host, the red-legged partridge (Alectoris rufa). We sampled 235 wild partridges from 8 separate localities, with different partridge population densities, in the Ciudad Real and Toledo provinces of central Spain, and we determined their overall and intestinal helminth species. We found that habitat variables (mean temperature and land use) were not significantly associated with any component community. The partridge population abundance index was directly correlated with the prevalence and mean intensity of infection but not with component community species richness. There was a curvilinear relationship between infracommunity and component community species richness, as well as negative interspecific associations, for the helminth species assemblage parasitizing the intestine. A nestedness/anti-nestedness pattern, considered as part of a continuum, was associated with prevalence, mean intensity and partridge population abundance index, but not with component community richness. Increases in the partridge population abundance index and the prevalence and mean intensity of infection were associated with increases in helminth community nestedness. Although negative interactions between helminth species could not be ruled out as forces structuring helminth communities, our results suggest that parasite community structure in the red-legged partridge was primarily determined by the extrinsic influence of parasite habitat heterogeneity and its amplification of the differing probabilities of colonization of parasite species.

Food habits of European badgers (Meles meles) along an altitudinal gradient of Mediterranean environments: a field test of the earthworm specialization hypothesis

Food specialization by European badgers (Meles meles) is a largely debated controversy. Data from Mediterranean areas indicate small importance of earthworms (Lumbricus spp.) in badger diet and support the idea that badgers are generalist predators. Nevertheless, only dry areas have been sampled so far. We studied badger diet in six areas along an elevation gradient with different rainfall and habitat conditions, which influenced earthworm availability. We evaluated the influence of earthworm availability on badger diet along this environmental gradient. Badgers used a wide range of prey items in the different habitats and seasons sampled. In contrast with other Mediterranean studies, earthworms made an important contribution to badger diet (27% of estimated volume). Earthworm occurrence in the diet was high in elevated and wet habitats and in spring and autumn–winter. Earthworm consumption was nonlinearly related to availability, indicating high intake compared with availability in wet areas. Moreover, in summer, availability was virtually zero in all habitats, whereas consumption averaged 15% volume of the diet. We tentatively suggest that badgers compensate for variations in earthworm availability by changing their foraging tactics. This suggests that badgers could be viewed as specialist foragers for earthworms in some Mediterranean environments.

Factors affecting wild boar (Sus scrofa) occurrence in highly fragmented Mediterranean landscapes

This paper is an analysis of the effects of forest fragmentation on wild boar (Sus scrofa) occurrence in coarse-grained fragmented landscapes (<20% forest–scrubland cover on a landscape scale; N = 140 forest fragments, four regions) in central Spain. Occurrence was examined in relation to forest size, isolation, habitat quality, and region. Wild boar occurrence was mainly explained by the location of the forest fragments on the northern or southern plateau. Wild boars were more abundant on the northern plateau than on the southern plateau. In addition, wild boars are more frequent in large forest fragments adjacent to other large forests near mountains or riparian woodlands. The percent presence of wild boars in fragments varied among the four regions sampled (regional effect). Although wild boars occurred more frequently in large than in small forests, this pattern was less pronounced than that found in badgers (Meles meles), roe deer (Capreolus capreolus), and stone martens (Martes foina) and similar to that found in red foxes (Vulpes vulpes). The spatial distribution of wild boars may be affected by forest fragmentation despite their typical generalist life-history traits and potential use of agricultural areas as food habitats. These results support the idea that landscape pattern (degree of fragmentation and grain pattern) may be a determinant of species' abundance and distribution in fragmented landscapes.

Factors determining "gaps" in the distribution of a small carnivore, the common genet (Genetta genetta), in central Spain

We studied the pattern of distribution of the common genet (Genetta genetta) in areas in mountains and plains of central Spain, in the middle of the range of the species. We evaluated the role of temperature, rainfall, and habitat features in determining the ecological limits of genet distribution. Genets were very scarce on plateaux and the upper parts of the mountains, but were widely distributed in lower mountain areas. Genets were present in areas with abundant shrub cover, high mean of the mean minimum temperature and high mean of mean winter temperatures. Survey routes at the same altitude (<1000 m) in the mountains (genets abundant) and on the plateaux (genets very scarce) also differed in some of these variables, with low values on the plateaux for shrub cover, mean of the mean minimum temperatures, mean of the mean winter temperatures, and annual rainfall. Genets originated in Africa, therefore they are probably ill-adapted (morphologically and physiologically) for the cold conditions predominating in most of central Spain. Their preference for shrubby habitats may be linked to a greater availability of food and low risk of predation. Intermediate levels of rainfall may be correlated with higher temperatures, the key factor hypothesized to affect the distribution of this species. The distribution of the common genet fits a multimodal model, with peaks (presence) and valleys (absence) in the middle of its range, indicating that location in a particular part of the range is not a prior indicator of habitat suitability for the species.

Roe deer habitat selection in Spain: constraints on the distribution of a species

This study analyzes the role of summer habitat selection in determining the distribution of a population of roe deer (Capreolus capreolus L.) in central Spain, where surplus individuals have emigrated from mountains to the surrounding plateaus during the last decade. The species was more abundant in the mesic mountain forests (Scots pine (Pinus sylvestris), Pyrenean oak (Quercus pyrenaica)) than in the xeric, sclerophyllous holm oak (Quercus ilex) forests of surrounding plateaus. Roe deer prefer patches occupied by brambles (Rubus spp.) and rose bushes (Rosa spp.) and patches with higher cover on pastures and moors (Erica spp. and Calluna spp.). These vegetation types are linked to moist soils in the Mediterranean zone, indicating that roe deer prefer the moister, more productive patches. Roe deer actively selected productive patches covered by leguminous shrubs (Sarothamnus, Retama) and rejected poor patches covered by Cistus ladanifer and Cistus laurifolius (two shrubs that produce chemicals toxic to other plants). Low summer primary productivity of xeric, sclerophyllous forests can explain the low abundance of roe deer in these forests. This supports the view that habitat constraints limit numbers and distribution of this Palaearctic species at the southern edge of its range.