Refine
Year of publication
Document Type
- Article (17)
- Postprint (4)
- Doctoral Thesis (1)
- Master's Thesis (1)
Is part of the Bibliography
- yes (23)
Keywords
- competition (23) (remove)
Bryophytes constitute an important and permanent component of the grassland flora and diversity in Europe. As most bryophyte species are sensitive to habitat change, their diversity is likely to decline following land-use intensification. Most previous studies on bryophyte diversity focused on specific habitats of high bryophyte diversity, such as bogs, montane grasslands, or calcareous dry grasslands. In contrast, mesic grasslands are rarely studied, although they are the most common grassland habitat in Europe. They are secondary vegetation, maintained by agricultural use and thus, are influenced by different forms of land use. We studied bryophyte species richness in three regions in Germany, in 707 plots of 16 m(2) representing different land-use types and environmental conditions. Our study is one of the few to inspect the relationships between bryophyte richness and land use across contrasting regions and using a high number of replicates. Among the managed grasslands, pastures harboured 2.5 times more bryophyte species than meadows and mown pastures. Similarly, bryophyte cover was about twice as high in fallows and pastures than in meadows and mown pastures. Among the pastures, bryophyte species richness was about three times higher in sheep grazed plots than in the ones grazed by cattle or horses. In general, bryophyte species richness and cover was more than 50% lower in fertilized than in unfertilized plots. Moreover, the amount of suitable substrates was linked to bryophyte diversity. Species richness of bryophytes growing on stones increased with stone cover, and the one of bryophytes growing on bark and deadwood increased with larger values of woody plant species and deadwood cover. Our findings highlight the importance of low-intensity land use and high structural heterogeneity for bryophyte conservation. They also caution against an intensification of traditionally managed pastures. In the light of our results, we recommend to maintain low-intensity sheep grazing on sites with low productivity, such as slopes on shallow soils.
Bryophytes constitute an important and permanent component of the grassland flora and diversity in Europe. As most bryophyte species are sensitive to habitat change, their diversity is likely to decline following land-use intensification. Most previous studies on bryophyte diversity focused on specific habitats of high bryophyte diversity, such as bogs, montane grasslands, or calcareous dry grasslands. In contrast, mesic grasslands are rarely studied, although they are the most common grassland habitat in Europe. They are secondary vegetation, maintained by agricultural use and thus, are influenced by different forms of land use. We studied bryophyte species richness in three regions in Germany, in 707 plots of 16 m2 representing different land-use types and environmental conditions. Our study is one of the few to inspect the relationships between bryophyte richness and land use across contrasting regions and using a high number of replicates.Among the managed grasslands, pastures harboured 2.5 times more bryophyte species than mead-ows and mown pastures. Similarly, bryophyte cover was about twice as high in fallows and pastures than in meadows and mown pastures. Among the pastures, bryophyte species richness was about three times higher in sheep grazed plots than in the ones grazed by cattle or horses. In general, bryophyte species richness and cover was more than 50% lower in fertilized than in unfertilized plots. Moreover, the amount of suitable substrates was linked to bryophyte diversity. Species richness of bryophytes growing on stones increased with stone cover, and the one of bryophytes growing on bark and deadwood increased with larger values of woody plant species and deadwood cover. Our findings highlight the importance of low-intensity land use and high structural heterogeneity for bryophyte conservation. They also caution against an intensification of traditionally managed pastures. In the light of our results, we recommend to maintain low-intensity sheep grazing on sites with low productivity, such as slopes on shallow soils.
My niche
(2020)
Intraspecific trait variation is an important determinant of fundamental ecological interactions. Many of these interactions are mediated by behaviour. Therefore, interindividual differences in behaviour should contribute to individual niche specialization. Comparable with variation in morphological traits, behavioural differentiation between individuals should limit similarity among competitors and thus act as a mechanism maintaining within-species variation in ecological niches and facilitating species coexistence. Here, we aimed to test whether interindividual differences in boldness covary with spatial interactions within and between two ecologically similar, co-occurring rodent species (Myodes glareolus, Apodemus agrarius). In five subpopulations in northeast Germany, we quantified individual differences in boldness via repeated standardized tests and spatial interaction patterns via capture-mark- recapture (n = 126) and automated VHF telemetry (n = 36). We found that boldness varied with space use in both species. Individuals of the same population occupied different spatial niches, which resulted in non-random patterns of within- and between-species spatial interactions. Behavioural types mainly differed in the relative importance of intra- versus interspecific competition. Within-species variation along this competition gradient could contribute to maintaining individual niche specialization. Moreover, behavioural differentiation between individuals limits similarity among competitors, which might facilitate the coexistence of functionally equivalent species and, thus, affect community dynamics and local biodiversity.
Density dependence is of fundamental importance for population and range dynamics. Density-dependent reproduction of plants arises from competitive and facilitative plant-plant interactions that can be pollination independent or pollination mediated. In small and sparse populations, conspecific density dependence often turns from negative to positive and causes Allee effects. Reproduction may also increase with heterospecific density (community-level Allee effect), but the underlying mechanisms are poorly understood and the consequences for community dynamics can be complex. Allee effects have crucial consequences for the conservation of declining species, but also the dynamics of range edge populations. In invasive species, Allee effects may slow or stop range expansion. Observational studies in natural plant communities cannot distinguish whether reproduction is limited by pollination-mediated interactions among plants or by other neighbourhood effects (e.g. competition for abiotic resources). Even experimental pollen supply cannot distinguish whether variation in reproduction is caused by direct density effects or by plant traits correlated with density. Finally, it is unknown over which spatial scales pollination-mediated interactions occur. To circumvent these problems, we introduce a comprehensive experimental and analytical framework which simultaneously (1) manipulates pollen availability and quality by hand pollination and pollinator exclusion, (2) manipulates neighbourhoods by transplanting target plants, and (3) analyses the effects of con- and heterospecific neighbourhoods on reproduction with spatially explicit trait-based neighbourhood models. Synthesis. By manipulating both pollen availability and target plant locations within neighbourhoods, we can comprehensively analyse spatially explicit density dependence of plant reproduction. This experimental approach enhances our ability to understand the dynamics of sparse populations and of species geographical ranges.
Parental effects (PE) can be adaptive and improve offspring performance when parents and offspring experience similar environmental conditions. However, it is unknown whether adaptive PE exist also in habitats where such similarity is unlikely due to strong temporal variation. In particular, we do not know whether PE can adapt offspring to fluctuating levels of neighbour competition in such habitats. Here, we tested for adaptive PE in terms of two key environmental factors in a semi-arid annual system, competition and drought. While rainfall was stochastic in the study site, the competitive environment was partly predictable: higher plant densities followed after favourable (rainy) years due to high seed production. We therefore expected PE to adapt the offspring's competitive ability to these (predictable) fluctuations in plant densities, rather than to adapt the offspring's drought tolerance to the (unpredictable) occurrence of intensified drought. Parental plants of Biscutella didyma, an annual Brassicaceae, were raised under favourable watering and under drought conditions. Offspring performance was then tested under a full-factorial combination of two neighbour regimes and six watering levels in the glasshouse. Offspring of parents grown under favourable conditions were stronger competitors. This was associated with a small shift in phenology but not with higher parental seed provisioning. Offspring from parents grown under drought showed no improved drought tolerance. Moreover, no PE were detectable when offspring were grown without neighbours. Our results suggest a novel path of adaptive PE: higher competitive ability was induced in offspring that were more likely to experience high neighbour densities. Together with the lack of adaptive PE towards drought tolerance, this emphasizes that a correlation between parental and offspring environment is crucial for adaptive PE to evolve. Our results also call for the inclusion of competitive effects in future PE studies.Synthesis. This study demonstrates the important role of adaptive PE for plant fitness (regarding competition) but also their limits (regarding drought) in temporally variable environments, based on the predictability of the respective environmental factor.
The competitive exclusion principle is one of the oldest ideas in ecology and states that without additional self-limitation two predators cannot coexist on a single prey. The search for mechanisms allowing coexistence despite this has identified niche differentiation between predators as crucial: without this, coexistence requires the predators to have exactly the same R* values, which is considered impossible. However, this reasoning misses a critical point: predators' R* values are not static properties, but affected by defensive traits of their prey, which in turn can adapt in response to changes in predator densities. Here I show that this feedback between defense and predator dynamics enables stable predator coexistence without ecological niche differentiation. Instead, the mechanism driving coexistence is that prey adaptation causes defense to converge to the value where both predators have equal R* values ("fitness equalization"). This result is highly general, independent of specific model details, and applies to both rapid defense evolution and inducible defenses. It demonstrates the importance of considering long-standing ecological questions from an eco-evolutionary viewpoint, and showcases how the effects of adaptation can cascade through communities, driving diversity on higher trophic levels. These insights offer an important new perspective on coexistence theory.
QuestionDisturbed areas offer great opportunities for restoring native biodiversity, but they are also prone to invasion by alien plants. Following the limiting similarity hypothesis, we address the question of whether or not similarity of plant functional traits helps developing seed mixtures of native communities with high resistance to invasive species at an early stage of restoration. LocationCentre of Greenhouses and Laboratories Durnast, Technische Universitat Munchen, Freising, Germany. MethodsUsing a system of linear equations, we designed native communities maximizing the similarity between the native and two invasive species according to ten functional traits. We used native grassland plants, two invasive alien species that are often problematic in disturbed areas (i.e., Ambrosia artemisiifolia and Solidago gigantea) and trait information obtained from databases. The two communities were then tested for resistance against establishment of the two invaders separately in a greenhouse experiment. We measured height of the invasive species and above-ground biomass, along with leaf area index, 4 and 8months after sowing respectively. ResultsBoth invasive species were successfully reduced by the native community designed to suppress S. gigantea dominated by small-seeded species. These results could be considered as partial support for the limiting similarity hypothesis. However, given the success of this mixture against both invasive species, suppression was better explained by a seed density effect resulting from the smaller seed mass of the native species included in this mixture. Further, the dominance of a fast-developing competitive species could also contribute to its success. ConclusionsThere was no unequivocal support for the limiting similarity hypothesis in terms of the traits selected. Instead we found that increasing seeding density of native species and selecting species with a fast vegetative development is an effective way to suppress invasive plants during early stages of restoration. If limiting similarity is used to design communities for restoration, early life-history traits should be taken into account.
Language production ultimately aims to convey meaning. Yet words differ widely in the richness and density of their semantic representations, and these differences impact conceptual and lexical processes during speech planning. Here, we replicated the recent finding that semantic richness, measured as the number of associated semantic features according to semantic feature production norms, facilitates object naming. In contrast, intercorrelational semantic feature density, measured as the degree of intercorrelation of a concept's features, presumably resulting in the coactivation of closely related concepts, has an inhibitory influence. We replicated the behavioral effects and investigated their relative time course and electrophysiological correlates. Both the facilitatory effect of high semantic richness and the inhibitory influence of high feature density were reflected in an increased posterior positivity starting at about 250 ms, in line with previous reports of posterior positivities in paradigms employing contextual manipulations to induce semantic interference during language production. Furthermore, amplitudes at the same posterior electrode sites were positively correlated with object naming times between about 230 and 380 ms. The observed effects follow naturally from the assumption of conceptual facilitation and simultaneous lexical competition and are difficult to explain by language production theories dismissing lexical competition.
1. Plant-plant interactions may critically modify the impact of climate change on plant communities. However, the magnitude and even direction of potential future interactions remains highly debated, especially for water-limited ecosystems. Predictions range from increasing facilitation to increasing competition with future aridification. 2. The different methodologies used for assessing plant-plant interactions under changing environmental conditions may affect the outcome but they are not equally represented in the literature. Mechanistic experimental manipulations are rare compared with correlative approaches that infer future patterns from current observations along spatial climatic gradients. 3. Here, we utilize a unique climatic gradient in combination with a large-scale, long-term experiment to test whether predictions about plant-plant interactions yield similar results when using experimental manipulations, spatial gradients or temporal variation. We assessed shrub-annual interactions in three different sites along a natural rainfall gradient (spatial) during 9 years of varying rainfall (temporal) and 8 years of dry and wet manipulations of ambient rainfall (experimental) that closely mimicked regional climate scenarios. 4. The results were fundamentally different among all three approaches. Experimental water manipulations hardly altered shrub effects on annual plant communities for the assessed fitness parameters biomass and survival. Along the spatial gradient, shrub effects shifted from clearly negative to mildly facilitative towards drier sites, whereas temporal variation showed the opposite trend: more negative shrub effects in drier years. 5. Based on our experimental approach, we conclude that shrub-annual interaction will remain similar under climate change. In contrast, the commonly applied space-for-time approach based on spatial gradients would have suggested increasing facilitative effects with climate change. We discuss potential mechanisms governing the differences among the three approaches. 6. Our study highlights the critical importance of long-term experimental manipulations for evaluating climate change impacts. Correlative approaches, for example along spatial or temporal gradients, may be misleading and overestimate the response of plant-plant interactions to climate change.
Strategic sexual signals
(2016)
The color red has special meaning in mating-relevant contexts. Wearing red can enhance perceptions of women's attractiveness and desirability as a potential romantic partner. Building on recent findings, the present study examined whether women's (N = 74) choice to display the color red is influenced by the attractiveness of an expected opposite-sex interaction partner. Results indicated that female participants who expected to interact with an attractive man displayed red (on clothing, accessories, and/or makeup) more often than a baseline consisting of women in a natural environment with no induced expectation. In contrast, when women expected to interact with an unattractive man, they eschewed red, displaying it less often than in the baseline condition. Findings are discussed with respect to evolutionary and cultural perspectives on mate evaluation and selection.