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Department of Ecology and Water Resources / MENVM

Future global change scenarios predict a dramatic loss of biodiversity for many regions in the world, potentially reducing the resistance and resilience of ecosystem functions. Once before, during Plio-Pleistocene glaciations, harsher climatic conditions in Europe as compared to North America led to a more depauperate tree flora. Here we hypothesize that this climate driven species loss has also reduced functional diversity in Europe as compared to North America. We used variation in 26 traits for 154 North American and 66 European tree species and grid-based co-occurrences derived from distribution maps to compare functional diversity patterns of the two continents. First, we identified similar regions with respect to contemporary climate in the temperate zone of North America and Europe. Second, we compared the functional diversity of both continents and for the climatically similar subregions using the functional dispersion-index (FDis) and the functional richness index (FRic). Third, we accounted in these comparisons for grid-scale differences in species richness, and, fourth, investigated the associated trait spaces using dimensionality reduction. For gymnosperms we find similar functional diversity on both continents, whereas for angiosperms functional diversity is significantly greater in Europe than in North America. These results are consistent across different scales, for climatically similar regions and considering species richness patterns. We decomposed these differences in trait space occupation into differences in functional diversity vs. differences in functional identity. We show that climate-driven species loss on a continental scale might be decoupled from or at least not linearly related to changes in functional diversity. This might be important when analyzing the effects of climate-driven biodiversity change on ecosystem functioning.

Grazing seems to be not only means of conserving species diversity of grasslands but also - in many cases - of its increasing. This thesis tries to find out the mechanisms of grazing that result in increased or decreased species diversity. The experiment was proceeded in Slupenec, a part of Český Krumlov, where horse pastures are situated. In order to compare grazing and mowing I collected phytosociological data from plots 1 x 1 mš. I also collected data about soil moisture, composition and pH in order to find out the main gradients in vegetation. The vegetation data from plots 20 x 20 cmš were collected before and after grazing on three pasturelands. In the chosen locality, higher level of plant species diversity have been proven on pastures in comparison with meadows. There is significantly higher percentage of plots contributing to the higher level of ß diversity on pastures than on meadows. At the same time the variability of vegetation was in most cases explained by the categorial variable pasture / meadow. Concerning selectivity of grazing, it has been proven that horses prefer grazing on species with greater cover abundance. The plots with lower rate of grazed species have got higher ß diversity. In terms of functional traits of plants, it has been proven that higher percentage of no-rosette...

De nombreuses études mettent en évidence un effet positif de la diversité spécifique sur la productivité des communautés végétales et la biodiversité associée. Mais l’effet de la diversité génétique sur la communauté d’espèces reste encore peu étudié en dépit des rares études montrant un effet positif avec des perspectives d’application dans le domaine de l’amélioration des plantes. C’est dans ce contexte que cette thèse s’interroge sur l’effet de la diversité génétique sur les communautés prairiales et la biodiversité du sol associée. Cette thèse repose sur une situation réelle via un dispositif d’évaluation de mélanges prairiaux installé par et chez un sélectionneur de plantes fourragères. Les résultats majeurs de cette thèse sont un effet positif de la diversité génétique des espèces sur la production de biomasse du mélange, particulièrement lors d’épisodes de sècheresse, et sur l’équilibre d’abondance des espèces. Ces effets positifs semblent être le résultat d’une différenciation de niches des espèces qui est à la base de la complémentarité des espèces en écologie. Il a été mis en évidence une complémentarité temporelle des espèces par une asynchronie des dynamiques de croissance, mais aussi une complémentarité sur l’acquisition de la lumière par des mécanismes de sélection et de plasticité. Enfin, des effets de la diversité génétique ont été observés sur la diversité microbienne avec des rétroactions potentielles sur les plantes. Au vu de ces résultats, il apparait que la diversité génétique occupe une place centrale dans l’assemblage et la structuration des communautés végétales et microbiennes, nous amenant à réfléchir quant à sa valorisation en amélioration des plantes. / Many studies highlight a positive effect of species diversity on plant community productivity and associated biodiversity. But genetic diversity effect on species community is still poorly studied despite the rare studies showing a positive effect with prospects for application in the field of plant breeding. It is in this context that this thesis examines the genetic diversity effect on grassland communities and associated soil biodiversity. This thesis is based on a real situation via an evaluation design of grassland mixtures installed by and in a plants breeding company. The major results of this thesis are a positive effect of the species genetic diversity on mixture biomass production, especially during drought episodes, and on species abundance equilibrium. These positive effects seem to be the result of a niche differentiation of species which is at the basis of species complementarity in ecology. Temporal complementarity of species has been demonstrated by asynchronous growth dynamics, but also by a complementarity for light acquisition via selection and plasticity mechanisms. Finally, genetic diversity effects have been observed on microbial diversity with plants feedbacks. In view of these results, it appears that genetic diversity occupies a central role in the assembly and structure of plant and microbial communities, leading us to consider how it could be integrated into plant breeding program.

It is now widely accepted that over one-third of the global food supply depends upon pollinators. Risking severe ecological and economic implications, the status of the 4000 species of bees native to North America has been poorly understood due to a lack of long-term survey data. In this study, I conducted bee surveys on Massachusetts cranberry (Vaccinium macrocarpon Ait.) bogs from 2007-2009 and compared diversity and abundance data to those from historical surveys performed in 1990-1992 on the same bogs. I found that overall bee diversity declined severely in the 19-year survey period, while total bee abundance remained consistent. My data provide supporting evidence for the loss of North American bumble bees (Bombus spp.), but also provide the first evidence for declines in the U.S. in overall wild bee diversity. Maximizing the potential for agricultural landscapes to serve as quality pollinator habitat and identifying appropriate integrated pest management strategies should involve a comprehensive understanding of each species’ life history traits and conservation status. The loss of biodiversity associated with the intensification of agriculture has been well documented for several wildlife species but remains poorly understood for bees, which provide pollination to many agricultural crops. Most pollinator-dependent crops rely heavily on managed honey bees (Apis mellifera L.) for pollination. Four thousand other species of bees native to North America may provide pollination insurance in the event of honey bee losses, but without a clear understanding of how agricultural intensification affects wild bees, habitat conservation measures aimed at protecting them may be futile. In the second part of this study, I evaluated six metrics of agricultural intensification with respect to native bee diversity and abundance in Massachusetts cranberry bogs, including honey bee competition, bog management type (i.e. organic versus conventional), distance from epicenter of cranberry-growing region, toxicity of insecticide program, susceptibility of reproductive bees to insecticide, and surrounding land use. I found a clear association between reduced native bee diversity and abundance and the effects of increased agricultural intensification of the landscape. Recognition that native bee communities in North America are diminishing as a consequence of agricultural intensification may help to unify a movement toward improved conservation management.

The dark kangaroo mouse, Microdipodops megacephalus, is a sensitive species in the Great Basin Desert. This thesis explores the structure of desert rodent communities of the Great Basin to better understand M. megacephalus' place in the community and the conditions that promote large and stable populations. To determine community structure, I used nestedness analysis to evaluate 99 communities of nocturnal granivorous rodents. I found that the community structure was non-random, indicating the existence of assembly rules and ecological constraints. I also found that M. megacephalus was the second most vulnerable species in the community. To explore the correlation between species diversity and relative abundance, I performed regression analyses on M. megacephalus and five commonly co-occurring species of the nocturnal granivore guild: Perognathus longimembris (little pocket mouse), Perognathus parvus (Great Basin pocket mouse), Dipodomys ordii (Ord's kangaroo rat), Dipodomys microps (chisel-toothed kangaroo rat), and Peromyscus maniculatus (deer mouse). Results showed a positive correlation between rodent species diversity and relative abundance for M. megacephalus, P. longimembris, P. parvus, and D. microps, and a negative correlation for D. ordii and P. maniculatus. To further understand community composition, I ran interspecific association analyses based on presence-absence data for the six species using chi-square to determine strength of interspecific associations. I found positive interspecific associations between M. megacephalus and P. parvus, between P. longimembris and P. parvus, between P. longimembris and D. microps, and between D. microps and P. maniculatus, and a negative association between P. longimembris and P. maniculatus. A species cluster dendogram with respect to sites in common further supports the interspecific association results. A site cluster dendogram with respect to species abundances implies that dune habitat promotes diversity but not uniformity. All results indicate that M. megacephalus is more abundant and stable at sites with high species richness. The results also provide evidence for the existence of assembly rules, competition, and niche partitioning in desert rodent communities.

This thesis is the culmination of a graduate research project involving a floristic survey of the lichens of the Spring Mountain National Recreation Area (SMNRA), Humboldt-Toiyabe National Forest, Nevada. The project was based on extensive collections made between 1997 and 2007 as part of an air pollution biomonitoring program and a baseline established by Larry St. Clair (BYU). The Spring Mountains are a sky island mountain range in the Mojave Desert located less than an hour northwest of Las Vegas. A floristic survey of the lichen communities in the Spring Mountains represents a major addition to our understanding of the lichen flora of the Mojave Desert, a poorly studied region in western North America. This thesis also compares the lichen flora of the SMNRA with other lichen floras of the Mojave Desert based on a literature survey of all the lichen studies conducted in the Mojave Desert. The SMNRA species list represents 58% of the 217 species in 68 genera reported for the Mojave Desert. This survey of all reported Mojave lichen species reveals several interesting interactions related to species diversity, substrate, and growth form distribution patterns. These interactions appear to be influenced by two general factors: Microhabitat conditions and available substrates – which are further defined by differences in geological substrates, occurrence and development of woody plant communities, and a combination of environmental factors – elevation, temperature, precipitation, and insolation. Drier and warmer habitats are generally dominated by crustose species with some, mostly smaller, foliose taxa in protected microhabitats usually with shaded or northern exposures. Fruticose species are generally lacking or sparse with smaller thalli when found in hot and dry habitats. All the fruticose species reported from the Mojave Desert sites were rare and had very small thalli. Many foliose and fruticose species, with larger, more complex thalli and thus greater surface area, are more susceptible to higher rates of water loss and therefore occur less frequently in extreme arid locations. The lichen communities in the Mojave Desert respond to sharp contrasts in microhabitat conditions with exposed, lower elevation sites having lower numbers of species along with more drought resistant growth forms – crustose and squamulose species. The Spring Mountains NRA, with high elevation mountains and well developed woody plant communities, accommodates a large variety of microhabitat conditions spread over a complex temperature and moisture gradient. These conditions have resulted in the highest species diversity (124 species in 48 genera) and the greatest number of foliose and corticolous species when compared with all of the other Mojave Desert lichen floras.

Mänskliga aktiviteter som till exempel urbanisering, har bidragit till förlusten av biologisk mångfald. En metod som man har föreslagit är att introducera gröna områden och plantera träd i stadsområden. Hypoteserna som testades i den här studien är att det finns en signifikant skillnad i trädartrikedom och trädartsdiversitet mellan tätorter och omgivande naturskogar i centrala Sverige; och att artrikedomen och diversiteten varierar mellan olika habitat i tätorterna. Studien utfördes inom fyra kommuner i Dalsland: Bengtsfors, Åmål, Dals-Ed och Mellerud. Man inventerade träd i fem olika habitater per kommun inom ett tätortsområde, samt ett naturskogsområde som ligger nära orten. Antalet trädarter och individuella träd beräknades och diversiteten inom varje kommun beräknades med hjälp av Shannon-Weavers diversitetsindex för det senare fallet. En signifikant skillnad i trädartrikedom och trädartsdiversitet uppmättes mellan ett tätortsområde och ett naturskogsområde (medianvärde på 10 respektive 3,5). Trädartrikedomen var högst i Bengtsfors med 13 olika trädarter och trädartdiversiteten var högst i Dals-Eds kommun (H’ = 1,22). En signifikant skillnad i trädartrikedom hittades, men inte i trädartsdiversitet. I tätorterna hade vattendrag det högsta medelvärdet i trädartrikedom tillsammans med förskolor med 4 trädarter. Den tidigare har också det högsta medelvärdet i trädartsdiversitet (H’ = 1,07). Resultaten stämde överens med den första hypotesen, men inte med den andra hypotesen. Sammanfattningsvis, är det välgörande att bibehålla och återställa gröna områden och träd i tätorter, och att det krävs mer forskning, för att föreslå strategier om att skydda biologisk mångfald och städerna från klimatförändringar och andra faror. / Anthropogenic activities, e.g. urbanization, have contributed to the loss to biological diversity. One method that has been proposed to combat urban biodiversity loss is to introduce green areas and to plant trees in urban areas. The hypotheses that were tested in this study are that; there is a significant difference in tree species richness and diversity between urban areas and surrounding natural forests in central Sweden; also, that the species richness and diversity varies between different habitats in urban areas. The study was performed in four municipalities in Dalsland: Bengtsfors, Åmål, Dals-Ed and Mellerud. Trees were inventoried in five different habitats per municipality within a suburban area, and in a natural forest area located near the locality. The number of tree species, individual trees, as well as the tree species diversity within each municipality were accounted for, with the use of Shannon-Weaver’s diversity index for the latter. A significant difference in tree species richness and diversity were found between suburban areas and surrounding natural forest areas (median of 10 and 3,5 respectively). The species richness was the highest in Bengtsfors’ municipality with 13 tree species, and the species diversity was the highest in Dals-Ed’s municipality (H’ = 1,22). A significant difference in tree species richness was found, but not in tree species diversity. In the suburban areas, sites near to water bodies had the highest average tree species richness, alongside kindergartens with 4 tree species. The former also has the highest average tree species diversity (H’ = 1,07). The results matched with the first hypothesis but did not match with second hypothesis. In conclusion, it is beneficial to maintain or restore green areas and trees in urban areas, and it requires more research, to propose strategies to protect biodiversity and cities from climate change and other dangers.

The vegetation responses to seven silvicultural treatments one growing season after harvesting were examined on seven sites in the southern Appalachian mountains of Virginia and West Virginia. Treatments included: 1) control, 2) understory control by herbicide, 3) group selection, 4) high-leave shelterwood, 5) low-leave shelterwood, 6) leave tree, and 7) clearcut. The effects of harvesting were compared between treatments and between pre-harvest and post-harvest samplings. Species richness, percent cover, and local species extinctions were calculated for sample plots ranging in size from 1m2 to 2 ha. Vegetation richness and cover increased with increasing harvest intensity. Local species extinctions were similar in the control and disturbed treatments. Additional analyses were performed using the control, high-leave shelterwood, and clearcut on five of the seven sites to determine the relationships between soil, litter, and other environmental characteristics and vegetation in the herbaceous layer (<1 m in height). Multivariate analysis techniques were used to analyze average differences in species abundance between pre-harvest and post-harvest and to relate post-harvest vegetation to microsite characteristics. Regional-scale differences in site location were more important in explaining the presence of a species than were environmental characteristics. Within a region, species primarily were distributed along a light/litter weight gradient and secondarily along a soil properties and nutrient gradient. / Master of Science