Jens Roland

Bio: Jens Roland is an academic researcher from University of Alberta. The author has contributed to research in topics: Population & Tent caterpillar. The author has an hindex of 35, co-authored 78 publications receiving 3760 citations. Previous affiliations of Jens Roland include University of British Columbia & Canadian Forest Service.

Insect parasitoid species respond to forest structure at different spatial scales

Abstract: There is now a solid body of theoretical work1–4 demonstrating that the spatial structure of the habitat combined with animal movement strongly influence host–parasitoid dynamics. The spatial pattern over which parasitoid search takes place can be affected by the distribution of the hosts5, by the spatial arrangement of the host's habitat6 and by the spatial scale at which the parasitoid perceives variation in host abundance7,8. Empirical work, however, has been largely restricted to small-scale field studies of less than one hectare6,9 with very few larger10,11. Here we report initial results of a many-year, large-scale study that is among the first to examine the interaction between a population-level process (parasitism) and anthropogenic forest fragmentation at large and at multiple spatial scales. We demonstrate that parasitism by four species of parasitoids attacking the forest tent caterpillar, Malacosoma disstria, is significantly reduced or enhanced depending on the proportion of forested to unforested land. Each of the parasitoid species responds to this mosaic at four different spatial scales that correspond to their relative body sizes. Our data give empirical support to the argument that changes in landscape structure can alter the normal functioning of ecological processes such as parasitism, with large-scale population consequences3,4.

Alpine parnassius butterfly dispersal: effects of landscape and population size

Abstract: We used mark–recapture methods to estimate the number of Parnassius smintheus (Papilionidae) butterflies moving among 20 alpine meadows separated by varying amounts of forest along the east slope of the Rocky Mountains in Alberta, Canada. We combined generalized additive models and generalized linear models to estimate the effects of intervening habitat type and of population size on butterfly movement. By incorporating habitat-specific distances between patches, we were better able to estimate movement compared to a strictly isolation-by-distance model. Our analysis estimated that butterflies move readily through open meadow but that forests are twice as resistant to butterfly movement. Butterflies also tended to stay at sites with high numbers of butterflies, but readily emigrate from sites with small populations. We showed that P. smintheus are highly restricted in their movement at even a fine spatial scale, a pattern reflected in concurrent studies of population genetic structure. As an example of th...

Influence of landscape on the population genetic structure of the alpine butterfly parnassius smintheus (Papilionidae)

Abstract: Four microsatellite DNA markers were developed which were used to examine the relationship between landscape and population genetic structure among a set of populations of the butterfly Parnassius smintheus located in the foothills of the Canadian Rockies. Detailed information on the dispersal of adult butterflies among this same set of populations was available. Simple and partial Mantel tests were used to examine the relationships between genetic distances, predicted rates of dispersal, and a number of landscape variables, all measured pairwise for 17 sample sites. Nei's standard genetic distance was negatively correlated with predicted dispersal. We observed a significant pattern of isolation by distance at a very small spatial scale. The distance between sites that was through forest was a stronger predictor of genetic distance than the distance through open meadow, indicating a significant effect of landscape on population genetic structure beyond that of simple isolation by distance. Our results suggest that rises in the tree-line in alpine areas, caused by global warming, will lead to reduced gene flow among populations of P. smintheus.

Large-scale forest fragmentation increases the duration of tent caterpillar outbreak

Abstract: I examined historical data (1950–1984) on the duration of outbreaks of the forest tent caterpillar (Malacosoma disstria) in northern Ontario, Canada. Outbreak duration was compared to host tree species dominance and forest structure over large areas of boreal forest partially cleared for agriculture. Abundance of the principal host tree species Populus tremuloides had no consistent effect on duration of outbreak within forest districts, and was negatively correlated with duration of outbreaks among the eight forest districts examined. The amount of forest edge per km2 was the best, and most consistent, predictor of the duration of tent caterpillar outbreaks both within individual forest districts and among forest districts. Because forest tent caterpillar populations are driven largely by the impact of parasitoids and pathogens, results here suggest that large-scale increase in forest fragmentation affects the interaction between these natural enemies and forest tent caterpillar. Increased clearing and fragmentation of boreal forests, by agriculture and forestry, may be exacerbating outbreaks of this forest defoliator.

The Theory of Island Biogeography

Abstract: Preface to the Princeton Landmarks in Biology Edition vii Preface xi Symbols Used xiii 1. The Importance of Islands 3 2. Area and Number of Speicies 8 3. Further Explanations of the Area-Diversity Pattern 19 4. The Strategy of Colonization 68 5. Invasibility and the Variable Niche 94 6. Stepping Stones and Biotic Exchange 123 7. Evolutionary Changes Following Colonization 145 8. Prospect 181 Glossary 185 References 193 Index 201

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Landscape perspectives on agricultural intensification and biodiversity – ecosystem service management

Abstract: Understanding the negative and positive effects of agricultural land use for the conservation of biodiversity, and its relation to ecosystem services, needs a landscape perspective. Agriculture can contribute to the conservation of high-diversity systems, which may provide important ecosystem services such as pollination and biological control via complementarity and sampling effects. Land-use management is often focused on few species and local processes, but in dynamic, agricultural landscapes, only a diversity of insurance species may guarantee resilience (the capacity to reorganize after disturbance). Interacting species experience their surrounding landscape at different spatial scales, which influences trophic interactions. Structurally complex landscapes enhance local diversity in agroecosystems, which may compensate for local high-intensity management. Organisms with high-dispersal abilities appear to drive these biodiversity patterns and ecosystem services, because of their recolonization ability and larger resources experienced. Agri-environment schemes (incentives for farmers to benefit the environment) need to broaden their perspective and to take the different responses to schemes in simple (high impact) and complex (low impact) agricultural landscapes into account. In simple landscapes, local allocation of habitat is more important than in complex landscapes, which are in total at risk. However, little knowledge of the relative importance of local and landscape management for biodiversity and its relation to ecosystem services make reliable recommendations difficult.

REVIEWS AND SYNTHESES Landscape perspectives on agricultural intensification and biodiversity - ecosystem service management

Abstract: Understanding the negative and positive effects of agricultural land use for the conservation of biodiversity, and its relation to ecosystem services, needs a landscape perspective. Agriculture can contribute to the conservation of high-diversity systems, which may provide important ecosystem services such as pollination and biological control via complementarity and sampling effects. Land-use management is often focused on few species and local processes, but in dynamic, agricultural landscapes, only a diversity of insurance species may guarantee resilience (the capacity to reorganize after disturbance). Interacting species experience their surrounding landscape at different spatial scales, which influences trophic interactions. Structurally complex landscapes enhance local diversity in agroecosystems, which may compensate for local highintensity management. Organisms with high-dispersal abilities appear to drive these biodiversity patterns and ecosystem services, because of their recolonization ability and larger resources experienced. Agri-environment schemes (incentives for farmers to benefit the environment) need to broaden their perspective and to take the different responses to schemes in simple (high impact) and complex (low impact) agricultural landscapes into account. In simple landscapes, local allocation of habitat is more important than in complex landscapes, which are in total at risk. However, little knowledge of the relative importance of local and landscape management for biodiversity and its relation to ecosystem services make reliable recommendations difficult.

Habitat Management to Conserve Natural Enemies of Arthropod Pests in Agriculture

Abstract: ▪ Abstract Many agroecosystems are unfavorable environments for natural enemies due to high levels of disturbance. Habitat management, a form of conservation biological control, is an ecologically based approach aimed at favoring natural enemies and enhancing biological control in agricultural systems. The goal of habitat management is to create a suitable ecological infrastructure within the agricultural landscape to provide resources such as food for adult natural enemies, alternative prey or hosts, and shelter from adverse conditions. These resources must be integrated into the landscape in a way that is spatially and temporally favorable to natural enemies and practical for producers to implement. The rapidly expanding literature on habitat management is reviewed with attention to practices for favoring predators and parasitoids, implementation of habitat management, and the contributions of modeling and ecological theory to this developing area of conservation biological control. The potential to int...