Restricted access to private properties limits management of invasive alien species: A literature review and case studies.

Biological invasions are one of the major drivers of global environmental change and there is a need to develop integrated strategies to counteract this phenomenon. Eradication is an effective management option to mitigate the deleterious impacts of invasive alien species (IAS). Eradication can be achieved if all reproductive individuals are removed and population recovery is prevented. However, individuals may survive removal operations in private areas if interventions are not allowed. Here, we present 1) three case studies in which restricted private property access prevented the local eradication of invasive alien populations, and 2) a list of reasons for denying access to private properties and a list of actions implemented or suggested by managers to facilitate access and reported in 29 reviewed papers. The restricted access affected the local eradication of three Eastern grey squirrel (Sciurus carolinensis) populations in Italy. In Lombardy region, in one area a planned eradication did not start and in another area the implemented eradication failed due to the refusal from the owner of a large private property to grant access to managers. In Umbria region, the lack of collaboration from an Italian financial institution produced a delay of 15 months in the removal. In our case studies, therefore, a single person or institution denied access for a personal gain or presumed internal security. The reasons behind landowner opposition may be diverse and individual attitudes towards IAS management will depend on interactions with owners. According to our review, in many cases the denial of access takes place in a general perception of mistrust or opposition to the project as the results of a limited engagement of local people. Such opposition often jeopardizes control activities, with profound negative consequences on eradication, expecially at landscape scale. Bottom-up approaches aiming at involving stakeholders can increase the possibility to achieve IAS eradication, however appropriate legislation remains pivotal to enforce eradication in case of non-cooperative behaviour.

Faecal egg counts from field experiment reveal density dependence in helminth fecundity: Strongyloides robustus infecting grey squirrels (Sciurus carolinensis).

Investigation of endo-macroparasite infections in living animals relies mostly on indirect methods aimed to detect parasite eggs in hosts' faeces. However, faecal flotation does not provide quantitative information on parasite loads, whereas faecal egg count (FEC) techniques may not give reliable estimates of parasite intensity, since egg production may be affected by density-dependent effects on helminth fecundity. We addressed this issue using Eastern grey squirrels (Sciurus carolinensis) and their gastrointestinal nematode Strongyloides robustus to assess the performance of coprological techniques and to investigate factors affecting parasite fecundity. We compared results of gut examination, flotation and McMaster FECs in 65 culled grey squirrels. Sensitivity and specificity of flotation were 81.2% (Confidence Interval, CI 54.3-95.9%) and 85.7% (CI 72.7-94.1%), respectively, resulting in low positive predictive values when infection prevalence is low. Individual parasite fecundity (no. of eggs/adult female worm) was negatively affected by S. robustus intensity, leading to a non-linear relationship between parasite load and eggs/gram of faeces (EPG). As a consequence, whereas flotation may be a valid method to perform the first screening of infection status, FECs are not a reliable method to estimate S. robustus intensity, since diverse values of EPG may correspond to the same number of parasites. Neither the amount of analysed faeces nor the season had any effect on EPG, indicating that the observed reduction in helminth fecundity is likely caused exclusively by density-dependent processes such as competition among worms or host immune response.

Geographical distance and physical barriers shape the genetic structure of Eurasian red squirrels (Sciurus vulgaris) in the Italian Alps.

Red squirrels (Sciurus vulgaris) are widely distributed throughout Eurasia, occurring in many types of coniferous and mixed-deciduous forests. In fragmented landscapes, small and partly isolated populations with low immigration rates show reduced genetic diversity, but reforestation can increase gene flow and restore levels of genetic variation in a few decades. No studies have so far investigated the genetic structure of red squirrel in large, continuous forests. The Italian Alps are presently characterized by almost continuous, recently reconnected forest habitats, that were affected by deep landscape changes during last glaciations but remained mostly unchanged between 10 000 and 200 years bp, when forest cover was heavily reduced. In this study we analyse patterns of genetic variability of red squirrels in and between seven sites distributed over 250 km of Alpine habitat, using mitochondrial DNA (mtDNA) and microsatellites. We use isolation-by-distance (IBD) models to investigate the relative importance that past (Pleistocene glaciations) and recent (fragmentation, bottlenecks) events had on the present genetic situation. Both nuclear and mtDNA data indicate a significant differentiation among study sites and a significant correlation between genetic and geographical distance only over a large scale. No recent bottlenecks are recorded through microsatellites and demographic models strongly support equilibrium between gene flow and drift; however, mtDNA suggests that there may have been local demographic crashes, probably in correspondence with the 19th-century forest fragmentation. These findings indicate that local landscape factors other than geographical distance per se, such as barriers of unsuitable habitat, affect gene flow and determine differentiation.

Fitness consequences of hoarding behaviour in the Eurasian red squirrel.

Hoarding increases food availability during periods of scarcity, and therefore should enhance fitness. Although short-term advantages of hoarding have been described for birds, effects over an animal's lifetime have not yet been documented. Here, we report that in the red squirrel, Sciurus vulgaris, individuals which recovered many cached tree seeds increased their body mass and were more likely to survive the spring breeding season than those that recovered fewer seeds. There was no significant effect of the time spent recovering cached food on the probability for females to produce a spring litter. In the long-term, hoarding behaviour was related to fitness in two ways; (i) squirrels spending more time recovering hoards survived longer; and (ii) females with a high recovery activity tended to wean more young in their lifetime than those that spent less time recovering hoards. Our data indicate that in red squirrels, food hoarding is an adaptive foraging strategy to preserve temporarily abundant food resources for future periods of hardship, and that individuals that hoard and recovery many tree seeds are more likely to survive and reproduce.

The effects of habitat fragmentation on demography and on the loss of genetic variation in the red squirrel.

A major problem in conservation biology is the extent to which the loss of genetic variability in isolated populations reduces their chance of survival. We present data in which the loss of genetic diversity in small and isolated populations can be directly related to population dynamics. Genetic similarity in red squirrels is inversely correlated with population size. The loss of genetic variation and the lower population densities in isolated populations are both the result of reduced immigration. Our data suggest that population processes rather than genetic problems are the real threat to small squirrel populations.