Impact of american mink on stone crayfish populations

1. Impact of introduced American mink (Mustela vison) predation on endangered stone crayfish (Austropotamobius torrentium) was examined in western Bohemian middle-sized streams for two years. Mink diet selectivity and its impact on its prey abundance were been investigating as the main target of this study. 2. The mink diet was described from excrements which were found on the target areas. The importance of different types of prey was specified by their relative numeric contribution to diet. The number of hunted crayfish was elicited from the number of crayfish remains which were collected during two years. The crayfish abundance was determined by capture {--} recapture method. 3. The crayfish was most frequently observed component of mink diet. The rate of mink predation on crayfish was dependent on density of crayfish population. This observed rate was lower during winters than during summers. The mink preferred significantly longer crayfish than was the mean of this value in population. 4. Although the crayfish was important part of mink diet the trend of impact of mink on crayfish is still inexplicit. It would be important to continue in this research to determine correlation between these two species

Fragmentation and mammalian carnivores in forest habitats: variables which affect carnivores distribution and habitat choice

The human use of landscape causes fragmentation and loss of original habitats. Different species vary in their sensitivity to habitat loss. Especially carnivores can be more sensitive to decrease of their habitat because of lower abundance of their prey. On the other hand several opportunistic carnivores can profit in human modified habitats. This study was carried out in the České Budějovice basin, Czech Republic during the years 2008 and 2009 and the aim of this study was to determine carnivore{\crq}s habitat preferences in the fragmented landscape. During these two years were seven carnivore species monitored in forest patches by using scent stations. Records of this monitoring were compared with physiognomy of these patches and structure of surrounding landscape

Barn Owl Productivity Response to Variability of Vole Populations.

We studied the response of the barn owl annual productivity to the common vole population numbers and variability to test the effects of environmental stochasticity on their life histories. Current theory predicts that temporal environmental variability can affect long-term nonlinear responses (e.g., production of young) both positively and negatively, depending on the shape of the relationship between the response and environmental variables. At the level of the Czech Republic, we examined the shape of the relationship between the annual sum of fledglings (annual productivity) and vole numbers in both non-detrended and detrended data. At the districts' level, we explored whether the degree of synchrony (measured by the correlation coefficient) and the strength of the productivity response increase (measured by the regression coefficient) in areas with higher vole population variability measured by the s-index. We found that the owls' annual productivity increased linearly with vole numbers in the Czech Republic. Furthermore, based on district data, we also found that synchrony between dynamics in owls' reproductive output and vole numbers increased with vole population variability. However, the strength of the response was not affected by the vole population variability. Additionally, we have shown that detrending remarkably increases the Taylor's exponent b relating variance to mean in vole time series, thereby reversing the relationship between the coefficient of variation and the mean. This shift was not responsible for the increased synchrony with vole population variability. Instead, we suggest that higher synchrony could result from high food specialization of owls on the common vole in areas with highly fluctuating vole populations

The relationship between barn owl productivity responses and vole population variability in ten districts of the Czech Republic.

<p>The upper panels show the degree of synchrony between the barn owl productivity and vole population variability using the non-detrending (a) and detrending approach (b). The lower panels show the strength of the productivity response to vole population variability without detrending (c) and with detrending (d). The dashed lines indicate 95% confidence intervals for the regression line.</p

(a) Map of the districts in the Czech Republic showing the distribution of barn owl nesting sites and (b) the dynamics of barn owl productivity (solid lines) and the common vole numbers (dashed line) in autumn during the period 1998–2013.

<p>The shaded areas in (a) indicate the 10 districts used in the analysis of vole population variability effects on the strength of the responses in the barn owl productivity parameters. Barn owl productivity was measured as the annual number of successfully produced fledglings (solid line). Vole numbers were measured by a vole index based on the number of active burrow entrances per hectare.</p

The Taylor’s power law relationships for the vole time series data.

<p>The upper panels show the relationship between variance and mean for non-detrended (a) and detrended (b) data. The lower panels show the relationship between the coefficients of variation (CV) and mean for non-detrended (c) and detrended (d) vole data.</p

The relationship between barn owl productivity responses and autumn vole index using non-detrended (a, c) and detrended (b, d) time series, based on the data from the whole Czech Republic.

<p>The barn owl responded to the increased vole population densities by increasing the mean number of clutches per site (a, b) and the mean number of fledglings per site (c, d). The regression was weighted by reciprocals of variance for annual means of owl productivity. The dashed lines indicate 95% confidence intervals for the regression line.</p