Thomas Secher Jensen

ALMaSS, an agent-based model for animals in temperate European landscapes

Abstract The animal, landscape and man simulation system (ALMaSS) was designed as a predictive tool for answering policy questions regarding the effect of changing landscape structure or management on key animal species in the Danish landscape. By combining agent-based models of animals with a comprehensive and dynamic landscape simulation, it aims to improve predictive ability. The landscape model comprises detailed mapping, weather, farm management, and vegetation growth. Each vegetated area has its own growth model and in the case of farmed areas, management is modelled in detail. Animal models are agent-based, designed using the state/transition concept, and are rule-based. Each animal may interact with others and directly with its local environment. Field vole ( Microtus agrestis ) is used as an example of the extent to which dynamic landscapes can influence the population dynamics. Simulations of crop diversity and rotation demonstrate significant effects of spatial and temporal heterogeneity on population sizes, population fluctuations and landscape permeability. These two factors interact and thus different responses to temporal factors occur at different levels of spatial heterogeneity. Spatial and temporal heterogeneity in both the model and the real world are often related to changes in land-use and management. Consequently, the impact of landscape changes on any population can be enormous and heavily spatially influenced. Therefore, the use of dynamic landscapes is seen as an important addition to the modeller’s toolkit.

Gene flow and population structure of a common agricultural wild species (Microtus agrestis) under different land management regimes.

The impact of landscape structure and land management on dispersal of populations of wild species inhabiting the agricultural landscape was investigated focusing on the field vole (Microtus agrestis) in three different areas in Denmark using molecular genetic markers. The main hypotheses were the following: (i) organic farms act as genetic sources and diversity reservoirs for species living in agricultural areas and (ii) gene flow and genetic structure in the agricultural landscape are influenced by the degree of landscape complexity and connectivity. A total of 443 individual voles were sampled within 2 consecutive years from two agricultural areas and one relatively undisturbed grassland area. As genetic markers, 15 polymorphic microsatellite loci (nuclear markers) and the central part of the cytochrome-b (mitochondrial sequence) were analysed for all samples. The results indicate that management (that is, organic or conventional management) was important for genetic population structure across the landscape, but that landscape structure was the main factor shaping gene flow and genetic diversity. More importantly, the presence of organically managed areas did not act as a genetic reservoir for conventional areas, instead the most important predictor of effective population size was the amount of unmanaged available habitat (core area). The relatively undisturbed natural area showed a lower level of genetic structuring and genetic diversity compared with the two agricultural areas. These findings altogether suggest that political decisions for supporting wildlife friendly land management should take into account both management and landscape structure factors.

No recent temporal changes in body size of three Danish rodents

We used museum collections to study temporal trends of possible changes in skull size, body mass and body length in three species of rodents in Denmark. Skulls of adult Microtus agrestis, Apodemus flavicollis and Apodemus sylvaticus, collected between 1895 and 2004, 1847 and 2002, and 1895 and 2002, respectively, were measured and data on body mass and length were taken from the museum registers. Principal component (PC) analysis was used to combine data of the four skull measurements taken. We tested the relationship of sex, latitude, longitude, month and year of collection to PC1 by a General Linear Model (GLM). PC1, body length and body mass of M. agrestis significantly increased from west to east. In addition, PC1, body mass and body length of M. agrestis declined from summer (August) through autumn and winter to spring (March), probably due to the decline in food availability towards winter. None of the other factors examined (sex, latitude and year) were significantly related to body size. PC1 of A. flavicollis and A. sylvaticus was not significantly related to any of the environmental factors examined.

Mice as stowaways? Colonization history of Danish striped field mice

Species from the steppe region of Eastern Europe likely colonized northwestern Europe in connection with agriculture after 6500 BP. The striped field mouse (Apodemus agrarius Pallas, 1783), is a steppe-derived species often found in human crops. It is common on the southern Danish islands of Lolland and Falster, which have been isolated from mainland Europe since approximately 10 300–8000 BP. Thus, this species could have been brought in with humans in connection with agriculture, or it could be an earlier natural invader. We sequenced 86 full mitochondrial genomes from the northwestern range of the striped field mouse, analysed phylogenetic relationships and estimated divergence time. The results supported human-induced colonization of Denmark in the Subatlantic or Subboreal period. A newly discovered population from Central Jutland in Denmark diverged from Falster approximately 100–670 years ago, again favouring human introduction. One individual from Sweden turned out to be a recent introduction from Central Jutland.