A comparison of small rodent assemblages after a 20 year interval in the Alps

Human-induced environmental alterations in the Alps may importantly affect small mammal species, but evidence in this sense is limited. We live-trapped small rodents in the Central-Eastern Italian Alps in three close-by habitat types (rocky scree, alpine grassland, and heath) at 2100 m a.s.l. during summer-fall, in 1997 and 2016. We compared small rodent assemblages through a Redundancy Detrended Analysis (RDA). In both surveys, we detected two specialist species, i.e., the common vole (Microtus arvalis) and the snow vole (Chionomys nivalis), and, unexpectedly, the forest generalist bank vole (Myodes glareolus). In 1997, grassland was mainly occupied by the common vole, while the bank vole and the snow vole were sympatric in the other habitats. In 2016, the snow vole was detected only in the scree, while other species did not show distribution changes. We discuss a series of hypotheses that might have driven the differences observed across decades, among which is a species-specific response to abiotic and biotic environmental alterations, with the alpine habitat specialist moving out of sub-optimal habitats. We encourage further research on this topic, e.g., via long-term longitudinal studies

Climate seasonality limits leaf carbon assimilation and wood productivity in tropical forests

The seasonal climate drivers of the carbon cycle in tropical forests remain poorly known, although these forests account for more carbon assimilation and storage than any other terrestrial ecosystem. Based on a unique combination of seasonal pan-tropical data sets from 89 experimental sites (68 include aboveground wood productivity measurements and 35 litter productivity measurements), their associate canopy photosynthetic capacity (enhanced vegetation index, EVI) and climate, we ask how carbon assimilation and aboveground allocation are related to climate seasonality in tropical forests and how they interact in the seasonal carbon cycle. We found that canopy photosynthetic capacity seasonality responds positively to precipitation when rainfall is < 2000 mm.yr−1 (water-limited forests) and to radiation otherwise (light-limited forests); on the other hand, independent of climate limitations, wood productivity and litterfall are driven by seasonal variation in precipitation and evapotranspiration respectively. Consequently, light-limited forests present an asynchronism between canopy photosynthetic capacity and wood productivity. Precipitation first-order control indicates an overall decrease in tropical forest productivity in a drier climate.Peer reviewe

Climate seasonality limits leaf carbon assimilation and wood productivity in tropical forests

The seasonal climate drivers of the carbon cycle in tropical forests remain poorly known, although these forests account for more carbon assimilation and storage than any other terrestrial ecosystem. Based on a unique combination of seasonal pan-tropical data sets from 89 experimental sites (68 include aboveground wood productivity measurements and 35 litter productivity measurements), their associated canopy photosynthetic capacity (enhanced vegetation index, EVI) and climate, we ask how carbon assimilation and aboveground allocation are related to climate seasonality in tropical forests and how they interact in the seasonal carbon cycle. We found that canopy photosynthetic capacity seasonality responds positively to precipitation when rainfall is  < 2000 mm yr⁻¹ (water-limited forests) and to radiation otherwise (light-limited forests). On the other hand, independent of climate limitations, wood productivity and litterfall are driven by seasonal variation in precipitation and evapotranspiration, respectively. Consequently, light-limited forests present an asynchronism between canopy photosynthetic capacity and wood productivity. First-order control by precipitation likely indicates a decrease in tropical forest productivity in a drier climate in water-limited forest, and in current light-limited forest with future rainfall  < 2000 mm yr⁻¹

Interspecific competition between mice and voles induced by ad libitum food resources: a simulation of climate change effects on sympatric species?

How resources are partitioned among sympatric species is conditional to extrinsic (e.g. climate driven) and intrinsic (e.g. demography-dependent) factors. To analyse these effects, we carried out a treatment-control experiment with supplemental ad libitum food accessible to the community of wild rodents, throughout seasons at two latitudinal extremes. We intensively live-trapped woodland rodents in north-eastern Italian Alps (2019 – 2021) and in south-eastern Norway (2013 – 2015), and applied multistate open robust design models to estimate the variability of demographic parameters under the experimental settings. Rodent assemblage was different at the two latitudes, with yellow-necked mouse, wood mouse (Apodemus spp.) and bank vole (Myodes glareolus) living in sympatry in Italy, whereas only bank vole occurred in Norway. In Norway, food scarcity and harsh climate seemed to limit rodent survival and abundance. In Italy, supplemental food promoted mice abundance, which in turn seemed to depress voles survival and abundance, most likely due to inter-specific behavioural and exploitative competition. The competitive mechanisms which we induced by providing ad libitum food resources may simulate population responses under climate change scenarios, with generalist species (e.g. Muridae) becoming prevalent part of the assemblage and overriding specialist species (e.g. Arvicolinae), also at the current extremes of their distribution range

Rodents and pathogens distribution along an altitudinal gradient in the Italian Alps

In a global change context, the association between generalists and specialists could be a determinant of ecosystem stability. This holds particularly true in mountain ecosystems, where the environmental tolerance of generalists to global warming may lead to their upward distributional shifts, while a decline is expected in specialists. As a consequence, even the parasites that these species carry can shift, eventually promoting the emergence of infectious diseases in newly colonized areas. We examined these relationships in small mammals along an altitudinal gradient in the Italian Alps (Province of Trento), where we identified 5 altitudinal belts from 500 to 2500 m a.s.l. with 500-meter intervals. We live-trapped small mammals applying capture-mark-recapture technique in 2019 and 2020. We counted ticks on rodents and collected blood and ear biopsy samples. Molecular PCR based methods coupled with sequencing and serological assays were performed for vector- and rodent-borne pathogens screening. We analysed probability of infection with Generalized Linear Mixed Models . Overall, we captured 333 animals belonging to 11 species (Apodemus flavicollis, A. sylvaticus, Chionomys nivalis, Microtus arvalis, M. subterraneus, M. agrestis, Myodes glareolus, Sorex araneus, S. alpinus, S. minutus, Crocidura leucodon). Apodemus spp. and My. glareolus were sympatric in the montane belt, from 500 to 1500 m a.s.l. My. glareolus was also present in the alpine belts, from 2000 to 2500 m, together with C. nivalis, Microtus spp. and shrews. We counted 3782 feeding-ticks belonging to the genus Ixodes. From the molecular screening of 324 ear samples we detected an unevenly altitudinal pattern of tick-borne pathogens distributions , with Borrelia spp. occurring up to 1500 m a.s.l. (prevalence 13.88%), while Anaplasma phagocytophilum (7.09%) and Babesia microti (3.08%) mainly recorded in alpine belts. We screened 440 sera samples and detected Dobrava virus in A. flavicollis (0.8%). Also 10% C. nivalis tested positive to both Dobrava/Puumala viruses. All samples tested negative for Tick-borne encephalitis virus. The observed altitudinal segregation in pathogens distribution revealed that this factor acted in a space-for-time way, mimicking the long-term temporal climatic variations expected under global warming. This may be explained by the presence of a more specialist endophilic tick species at higher altitudes that solely utilize small mammals as hosts for all developmental stages (e.g., Ixodes trianguliceps). Moreover, our findings supported the expansion of the generalist species My. glareolus toward higher altitudes, where specialists, such as C. nivalis, resulted restricted only in some specific habitats. The potential replacement of specialists by generalists can cause an homogenization at the community level, which in turn could alter ecosystem functioning and host-parasite-pathogen association, with implication for spreading of emerging infectious diseases

Host aggregation and local density corresponds to heterogeneity in tick-borne and rodent-borne diseases

Host-parasite-pathogen dynamics in nature have been linked to a range of extrinsic and intrinsic factors, which shape the spatio-temporal heterogeneity of environment. Here we evaluated how anthropogenic food manipulation may affect hosts local density and space-use patterns, parasite burden, and pathogen prevalence The study was carried out from February 2019 to April 2021 in Cembra Valley (Trentino, Italian Alps), in a treatment-control field experiments. Treatment sites were at ungulate feeding sites dispensing supplemental ad libitum food, where roe deer were being captured and marked with GPS collars, whereas control sites were placed at least 500 m away from the closest feeding site. In both treatment and control sites, we performed monthly live capture-mark recapture of rodents by individually marking captured individuals with Passive-Integrated Transponder (PIT) tag. Standard capture information, life-history traits and parasites’ presence were recorded, while biological samples (blood, tissue, faeces) were collected. We applied Spatially Explicit-Capture-Recapture models to spatially predict rodent density and space-use patterns, while we relied on GPS telemetry data to perform a recursion analysis with the aim of assessing roe deer revisitation patterns at treatment and control sites. Through Generalized Linear Mixed Models, we modelled how mice tick burden varied in dependence on the presence of ungulate feeding sites, rodent density and phenotypic traits (sex, status and body mass). Additionally, serological assays and molecular PCR-based methods coupled with sequencing were performed to assess the prevalence of rodent- and vector-borne pathogens at control and treatment sites. 398 yellow-necked and wood mice (Apodemus spp.), 109 bank voles (Myodes glareolus) and 12 roe deer individuals were captured at treatment sites. The availability of supplemental food shrunk rodents’ space-use, increasing mice but not voles local densities. Roe deer revisitation rate was significantly higher at treatment respect to control sites. 1790 feeding Ixodidae ticks were counted on rodents. Tick burden was significantly higher in heavier individuals, but did not depend on site. Conversely, spatial pattern of rodent- (Dobrava-Belgrade and Puumula viruses) and vector-borne (Tick-borne Encephalitis virus, Borrelia afzelii, Babesia microti, Anaplasma phagocytophylum and Hepatozoon spp.) pathogens occurrence varied among control and treatment sites. Vector-borne pathogens showed a lower prevalence at feeding sites (mean prevalence, 8.69%) than at control sites (13.89%), while the opposite was found for rodent-borne ones (1.55% and 1.16%, respectively). Our findings suggest that both woodland rodents and roe deer were attracted by supplemental food resources. We argue that the co-occurrence of incompetent (roe deer) and competent hosts (rodents) at these sites might affect infectious pathogens’ spreading. These results underline the importance of considering spatial distribution of competent and incompetent hosts, and not only overall density, to investigate zoonotic ris

Are generalists species replacing specialists? Implications of hosts species distribution on tick-borne diseases along an altitudinal gradient in the Italian Alps.

Introduction In a global change context, the association between generalists and specialists could be a determinant of ecosystem stability. This holds particularly true in mountain ecosystems, where the environmental tolerance of generalists to global warming may lead to upward distributional shifts and thus declining of specialists. As a consequence of this altitudinal expansion, even the parasites that these species carry can shift, eventually promoting the emergence of infectious diseases in newly colonized areas. We examined these relationships in small mammals along an altitudinal gradient of Alpine habitats, analysing the differences in small mammals’ assemblage and pathogens’ occurrence. Methods We capture-mark-recaptured wild small mammals from 500 to 2500 m a.s.l. at 500-meters intervals in the Italian Alps, in 2019 and 2020. We counted ticks on rodents and collected ear biopsy samples. Molecular PCR-based methods coupled with sequencing and serological assays were performed for vector-borne pathogens screening. We analysed small mammal species assemblages and probability of infection along the altitudinal gradient with Redundancy Detrended Analysis (RDA) and Generalized Linear Mixed Models (GLMMs). Results In total we captured 333 animals belonging to 11 species (Apodemus flavicollis, A. sylvaticus, Chionomys nivalis, Microtus arvalis, M. subterraneus, M. agrestis, Myodes glareolus, Sorex araneus, S. alpinus, S. minutus, Crocidura leucodon) and counted 3782 ticks (3718 larvae and 64 nymphs) belonging to the genus Ixodes. A. flavicollis and My. glareolus occupied in sympatry the montane belts, from 500 to 1500 m a.s.l. My. glareolus was also present in the alpine belts, from 2000 to 2500 m, together with C. nivalis, Microtus spp. and shrews. We also detected an unevenly altitudinal pattern of distributions of vector-borne pathogens, with Borrelia spp. occurring up until 1500 m a.s.l. (prevalence 13.88%), while Anaplasma phagocytophilum (7.09%) and Babesia microti (3.08%) mainly recorded in alpine belts. Conclusions Wild rodents are important reservoirs of numerous tick-borne pathogens. The altitudinal segregation that we found, revealed that also parasites are affected by climate, as shown by the presence of A. phagocytophilum and B. microti at higher altitudes where I. ricinus has never been recorded. This made us speculate on the presence of a more specialist endophilic tick species that solely utilize small mammals as hosts for all developmental stages (such as Ixodes trianguliceps). Moreover, our findings support the expansion of the generalist species My. glareolus toward higher altitudes, where specialists, such as C. nivalis, were restricted only in some specific habitats. The potential replacement of specialists by generalists can cause an homogenization at the community level which in turn could alter ecosystem functioning, including the host-parasite-pathogen association with implication for emerging infectious diseases spread