Pablo Ferreras

Effects of an Attractive Sink Leading into Maladaptive Habitat Selection

Habitat sinks can attract dispersing animals if high mortality or breeding failure are difficult to detect (e.g., when due to human hunting or pollution). Using a simple deterministic model, we explore the dynamics of such source‐sink systems considering three scenarios: an avoided sink, no habitat preference, and an attractive sink. In the second two scenarios, there is a threshold proportion of sink habitat above which the whole population decreases to extinction, but this extinction threshold varies with habitat preference and the relative qualities of the two habitat types. Hence, it would be necessary to know the habitat preferences of any species in a source‐sink system to interpret data on population increases and declines. In the attractive sink scenario, small changes in the proportion of sink habitat may have disproportionate effects on the population persistence. Also, small changes in growth rates at the source and the sink severely affect the threshold and the time of extinction. For some combinations of demographic parameters and proportion of habitat sink, the decline affects the source first; thus, during some time, it will be hidden to population monitoring at the sink, where numbers can even increase. The extinction threshold is also very sensitive to the initial population sizes relative to carrying capacity. Attractive sinks represent a novel aspect of source‐sink dynamics with important conservation and management implications.

Effects of Matrix Heterogeneity on Animal Dispersal: From Individual Behavior to Metapopulation‐Level Parameters

Mounting theoretical and empirical evidence shows that matrix heterogeneity may have contrasting effects on metapopulation dynamics by contributing to patch isolation in nontrivial ways. We analyze the movement properties during interpatch dispersal in a metapopulation of Iberian lynx (Lynx pardinus). On a daily temporal scale, lynx habitat selection defines two types of matrix habitats where individuals may move: open and dispersal habitats (avoided and used as available, respectively). There was a strong and complex impact of matrix heterogeneity on movement properties at several temporal scales (hourly and daily radiolocations and the entire dispersal event). We use the movement properties on the hourly temporal scale to build a simulation model to reconstruct individual dispersal events. The two most important parameters affecting model predictions at both the individual (daily) and metapopulation scales were related to the movement capacity (number of movement steps per day and autocorrelation in dispersal habitat) followed by the parameters representing the habitat selection in the matrix. The model adequately reproduced field estimates of population‐level parameters (e.g., interpatch connectivity, maximum and final dispersal distances), and its performance was clearly improved when including the effect of matrix heterogeneity on movement properties. To assume there is a homogeneous matrix results in large errors in the estimate of interpatch connectivity, especially for close patches separated by open habitat or corridors of dispersal habitat, showing how important it is to consider matrix heterogeneity when it is present. Movement properties affect the interaction of dispersing individuals with the landscape and can be used as a mechanistic representation of dispersal at the metapopulation level. This is so when the effect of matrix heterogeneity on movement properties is evaluated under biologically meaningful spatial and temporal scales.

Spatial relationships between Iberian lynx and other carnivores in an area of south-western Spain

1. Spatial relationships between Iberian lynx and other carnivores were studied by radio-tracking and/or track censusing in two adjacent areas of Donana (south-western Spain). 2. Both radio-tracking and track censusing showed that lynx were restricted to an undisturbed area of Pistacia lentiscus shrubs called Matasgordas. Minimum and maximum lynx density in Matasgordas were estimated as 0.55 and 0.75 ind. km -2 . 3. Egyptian mongoose tracks were mainly detected outside Matasgordas (83% of tracks), European badger tracks were detected most often inside Matasgordas (76% of tracks), and red fox tracks were frequently detected both outside (54%) and inside (46%) Matasgordas. Surveys of tracks and faeces undertaken in other 14 areas where P. lentiscus shrubs also dominated corroborated the census data obtained inside and outside Matasgordas. 4. Trapping and radio-tracking of mongooses and common genets indicated that both species avoided use of Matasgordas. They were almost exclusively trapped (24 out of 25 mongooses and all of 11 genets) and mainly radio-located (94.5% and 95.4% of times, for mongooses and genets, respectively) in the areas of P. lentiscus shrubs situated outside Matasgordas. Their densities were estimated as 0.2 and 0.03 ind. km -2 inside, and as 2.0 and 0.7 ind. km -2 outside Matasgordas for mongooses and genets, respectively. 5. Lynx may kill mongooses, genets, and foxes ; thus, the avoidance of Matasgordas by smaller carnivores (mongooses and genets) could be related to the risk of lynx predation. It is suggested that the decline of the lynx in the Donana area may have caused the increase in the population size of smaller, previously rarer carnivores. 6. The true relationship between lynx and foxes remains unclear, and badgers were apparently indifferent to lynx presence or absence.

Rates and causes of mortality in a fragmented population of Iberian lynx Felis pardina Temminck, 1824

Abstract Data are presented on mortality rates of the Iberian lynx Felis pardina in Donana National Park and the surrounding area in southwestern Spain, collected from 1983 to 1989. Data from radio-tagged lynxes and records of lynx mortality were used to assess causes of death. Annual mortality rate, estimated by using the Heisey and Fuller methodology, was 0·37. Human activities were the main cause of lynx mortality in this mainly fully protected area, either directly (illegal trapping: 41·7%; road traffic: 16·7%; hunting with dogs: 8·3%) or indirectly (artesian wells: 8·3%). Only 8·3% of the annual mortality can be related unequivocally to natural causes. Sex, age, social status, year, and home range situation influenced mortality rates. The trend of this lynx population during the seven years of study revealed serious threats to its survival. This case study exemplified how a small population can approach extinction because of increased mortality due to habitat fragmentation, despite full protection of the main portion of its range.

Rabbit populations and game management: the situation after 15 years of rabbit haemorrhagic disease in central-southern Spain

Over recent decades wild rabbit populations have undergone a sharp decline in Spain with consequent negative impact both on a game-based economy, and on the conservation of threatened species that depend on rabbits. We investigated the relationships between rabbit population change and habitat and game management in central-southern Spain. To determine recent rabbit population changes we revisited 60 localities during summer 2002 to repeat surveys previously carried out in 1993. Each survey consisted of 4-km walked transects to record indices of rabbit abundance. The percentage of vegetation cover and of different soil types were also estimated during these transects. In the same areas, the type and intensity of game management practices were obtained by interviewing hunting managers, hunters or gamekeepers. Rabbit populations were stable or increasing only in 26.6% of the studied populations, more commonly in areas with soft soils where warren building is easier for rabbits and where rabbits were an important game species and managed to increase their numbers. Although we could not establish causality, habitat management and predator removal were the main management practices related to rabbit population change. Rabbit scarcity in Spain constitutes a serious problem for conservation, so hunters, researchers and policy makers need to reach a consensus to establish a long-term program to monitor rabbit population trends and share results obtained, especially when intense manage programs are being carried out to improve rabbit abundance.

Translocations as a risk for the conservation of European wild rabbit Oryctolagus cuniculus lineages

Population units that merit separate management and are of conservation concern have been called evolutionary significant units. Two divergent lineages of the European rabbit Oryctolagus cuniculus occur naturally in Spain, with a well-marked geographical distribution. We analysed the frequency and importance of rabbit translocations in central-southern Spain and whether this practice, carried out by hunters and conservationists, could cause the mixture of two clearly different evolutionary significant units. We carried out interviews in 1993 and 2002 at 60 locations to determine the presence and intensity of translocations during both decades. The distribution of the lineages was obtained using mtDNA analysis of hunted rabbits in 2003-2005. We demonstrate that rabbit translocation was used frequently in the 1980s and increased in the 1990s. Up to 43% of the studied areas translocated rabbits in the latter decade, whereas only 25% did so in the 1980s. Our results show that neither the origin of the introduced rabbits nor their genetic lineage were taken into account in most of the translocations. We found rabbits of lineage A in several localities within the distribution area of lineage B, and vice versa, probably as a consequence of translocations. The distribution of both lineages is likely to have been altered by human activity and this could represent the loss of the results of 2 million years of genetic differentiation with possible attendent ecological consequences. Consequently, authorities should more closely regulate rabbit translocations and convey to both hunters and conservationists the importance of not mixing the lineages by translocations.

Restore habitat or reduce mortality? Implications from a population viability analysis of the Iberian lynx

Managers trying to preserve populations of endangered carnivores are often forced to choose between restoring habitat to allow larger breeding populations or reduce risks of mortality to increase survival rates. We modelled the viability of a metapopulation of the Iberian lynx ( Lynx pardinus ) under several scenarios (habitat restoration, anti-poaching, reduction in road kills) in a real landscape to evaluate their relative effects. Increasing carrying capacity was highly effective when performed on the local populations that acted as sources but had no effect when carried out in the sinks. Realistic scenarios consisting of partial removal of the human-related mortality (assuming additive effects of causes) predicted high risk of extinction. When combined, the effects of both management options are highly dependent on where they are carried out. If the sinks are the only targets of carrying capacity enlargement, a complete removal of human-caused mortality is required, whereas increases in the carrying capacity of sources are always effective. The metapopulation risk of extinction decreases dramatically (from 45.5% to 2.1% in 100) if connectivity among source populations can be improved. According to our work, only a detailed knowledge of the spatial and demographic structure of the populations, combined with simulations of realistic situations, can help managers to select the a priori optimal strategy, which probably combines different management options.

Co-existence between Iberian lynx and Egyptian mongooses: estimating interaction strength by structural equation modelling and testing by an observational study

We used path analysis to investigate the causal relationships between Iberian lynx and Egyptian mongoose track numbers, and to estimate the direct effect of the former on the latter in the Doñana area (2750 km(2) ), south-western Spain. Relative abundance of rabbits, shrub cover and protection level were also considered in the path analysis. An observational study consisting of a repeated track survey with a split-plot design was also carried out between 1990 and 1996 to independently test the results obtained by path analysis. Maximum likelihood ratio tests of the goodness-of-fit of the model to the data and other indices used all indicated that the proposed theoretical model depicting the relationships among variables was adequate. Egyptian mongooses suffered a significant direct negative effect from lynx, and rabbits and protection level positively, and significantly affected lynx track abundance; rabbits were also significantly affected by shrub cover (all these standardized partial correlation coefficients ranged from 0.34 to 0.41). Shrub cover did not directly affect either lynx or mongoose tracks. Relatively important indirect effects were found between shrubs and lynx (0.12), and between rabbits and mongooses (-0.14), and protection and mongooses (-0.17). The two latter non-intuitive indirect effects were through the lynx path, as a consequence of the negative direct influence of lynx on mongooses. The repeated track censuses confirmed that lynx presence significantly affects number of mongoose tracks. In areas without lynx, mean number of mongoose tracks were 3.6 times higher than in areas with lynx. It remains an interesting question which of several proposed hypotheses explains co-existence of both species in south-western Spain.

Feeding responses of the red fox (Vulpes vulpes) to different wild rabbit (Oryctolagus cuniculus) densities: a regional approach

We investigate the feeding responses of the red fox (Vulpes vulpes) at a regional scale to different densities of European wild rabbit (Oryctolagus cuniculus) in central–southern Spain. Rabbit abundance indices were obtained in 86 localities during summer 2002. The diet of the fox was studied by analysis of 114 scats collected in 47 of these localities. The feeding response of the fox was examined by a representation of the dry weight percent of rabbit in the diet as a function of the abundance of rabbits; this used data only from those localities where at least 3 scats were collected (70 fox scats from 18 localities). We evaluated the relationship between rabbit abundance and the diversity of the diet of the fox. The feeding patterns of red foxes approximated to Holling’s type III functional response, typical of opportunistic predators. There was a negative relationship between the diversity of the fox’s diet and the abundance of rabbits. Therefore, the fox apparently behaves as a facultative predator, feeding on rabbits when they are abundant and shifting to other prey (and hence a more diverse diet) when rabbits are scarce. These findings are the first step towards understanding the potential role of red foxes in regulating rabbit populations in central–southern Spain.

Local and landscape habitat determinants of water vole distribution in a patchy Mediterranean environment

Abstract We studied the distribution of a water-dependent species (southern water vole, Arvicola sapidus) in a Mediterranean region (Doñana National Park, southwest Spain) characterized by a complex array of different-sized ponds (where voles were confined) embedded in a mostly unsuitable landscape. For each surveyed pond (n = 185), a total of 26 variables related to both local (20) and landscape (6) attributes were quantified, and the presence of voles was evaluated by finding their typical signs (latrines). We found signs of water voles in 60% of ponds, despite the fact that most of them (84%) were totally dried out. A generalized linear model analysis showed that water voles were sensitive to both local and landscape attributes of ponds. At a landscape scale, presence of voles was more likely in ponds located outside the national park, close to other ponds holding voles, and far away from areas rich in potential predators and competitors. At a local scale, ponds with water voles were characterized by abundant grasses, banks well covered by brushes, low altitude, and low abundance of rabbits (Oryctolagus cuniculus). We also studied the use of microhabitat by voles within four specific ponds and found that they preferred plots of higher vegetation cover; thus, there was consistency in some cues used by water voles at the population/subpopulation scale (among different ponds) and at the behavioral scale (within ponds). Our study strongly supports the notion that the entire vole population is structured in distinct subpopulations, which are affected by a hierarchy of processes ranging from metapopulation dynamics and influenced by the landscape within which ponds are embedded as well as the local habitat quality.