High habitat richness reduces the risk of tick-borne encephalitis in Europe: A multi-scale study

Background

The natural transmission cycle of tick-borne encephalitis (TBE) virus is enhanced by complex interactions between ticks and key hosts strongly connected to habitat characteristics. The diversity of wildlife host species and their relative abundance is known to affect transmission of tick-borne diseases. Therefore, in the current context of global biodiversity loss, we explored the relationship between habitat richness and the pattern of human TBE cases in Europe to assess biodiversity's role in disease risk mitigation.

Methods

We assessed human TBE case distribution across 879 European regions using official epidemiological data reported to The European Surveillance System (TESSy) between 2017 and 2021 from 15 countries. We explored the relationship between TBE presence and the habitat richness index (HRI1) by means of binomial regression. We validated our findings at local scale using data collected between 2017 and 2021 in 227 municipalities located in Trento and Belluno provinces, two known TBE foci in northern Italy.

Findings

Our results showed a significant parabolic effect of HRI on the probability of presence of human TBE cases in the European regions included in our dataset, and a significant, negative effect of HRI on the local presence of TBE in northern Italy. At both spatial scales, TBE risk decreases in areas with higher values of HRI.

Interpretation

To our knowledge, no efforts have yet been made to explore the relationship between biodiversity and TBE risk, probably due to the scarcity of high-resolution, large-scale data about the abundance or density of critical host species. Hence, in this study we considered habitat richness as proxy for vertebrate host diversity. The results suggest that in highly diverse habitats TBE risk decreases. Hence, biodiversity loss could enhance TBE risk for both humans and wildlife. This association is relevant to support the hypothesis that the maintenance of highly diverse ecosystems mitigates disease risk.

Woodland features determining home range size of roe deer

Use of ecotones by ungulates may be mediated by their movements between main feeding areas and woodland, where they locate their shelter. The roe deer Capreolus capreolus has been termed as a woodland species, although we suggest that it did not evolve as a forest ungulate, but depending on forest glades. Roe deer feed on a wide range of vegetal species, although their diet is mainly dominated by woody plants. Our study was carried out in a fragmented area covered with small forest patches of Mediterranean "macchia" scrubwood, interspersed in an agricultural matrix. Aim of our study has been to test how ranging movements of roe deer are influenced by landscape heterogeneity and to evaluate which features of woodland affect home range size. Radio-locations of 22 female and 12 male adult roe deer, monitored for three years, were used to assess home range size. A linear mixed model was fitted to investigate variation in home range size according to eleven spatial parameters estimated to describe home range size and composition. Throughout the year, no significant difference was found between home range sizes of males (median: 16.70ha, Q₁-Q₃: 13.20-31.60ha) and females (median: 23.52ha, Q₁-Q₃: 13.30-44.00ha: lme: F=0.9; P=0.35). Habitat density, edge density, percentage of woodland within home range and woodland structure determined home range size. Home ranges with few habitat types and a small amount of wood were large, while roe deer occupied small home ranges when habitat density was high and when a high proportion of wood was concentrated in a single large patch. Woodland covered a mean±SE of 36.2±17.9% in each home range. In conclusion, roe deer seem to be particularly well adapted to live in human transformed, peripheral habitats, e.g. farmlands, as long as a minimum quantity of woodland is included within their HR.