Physical supporting or defense structures of plants, which decrease palatability, remain in plant tissue after a plant’s death and so decrease detritus decomposition rates. Consequently, palatability and detritus decomposition rate are expected to be positively correlated. Carbon is the main component of these restricting structures, whereas nitrogen is expected to increase plant attractiveness for herbivores. In this study, we tried to confirm the expected positive relationship between palatability and detritus decomposition rate and to find the species functional traits that are responsible for this concordant response. Some traits are shared by species as a consequence of their common phylogenetic history; consequently, we also studied the effect of phylogenetic correction on the expected relationships.We assessed the palatability of meadow plant species to a generalist slug
in an aquarium grazing experiment and detritus decomposition rate in a field litter-bag test. The two characteristics are positively correlated and the relationship is strengthened by phylogenetic correction. The relationship was strongest for the decomposition rates during the first three months of exposition, but weakened when the exposition period was from six months to a year. Palatability was negatively affected by plant carbon content, but no relationship was found between plant palatability and nitrogen content. Similarly, only the relationship of litter decomposition with litter carbon content was significant. The regression tree method was used to detect the influence of species traits on species palatability and detritus decomposition rate. In general, leaf dry matter content, litter carbon content and seed weight were chosen as the best predictors of plant palatability response. Results for the detritus decomposition rate response mainly reflect supporting or defensive structure contents. Litter carbon content, seed weight and plant height are the most apparent common predictors of these variable responses.In general, our study confirmed the positive relationship between plant palatability and detritus decomposition. Both plant tissue grazing and detritus decomposition are slowed down by plant tissue supportive structures, manifested as high dry matter content or high tissue carbon content.
Traditionally, species absence in a community is ascribed either to dispersal limitation (i.e., the inability of propagules of a species to reach a site) or to habitat limitation (abiotic or biotic conditions of a site prevent species from forming a viable population); sowing experiments can then distinguish between these two mechanisms. In our view, the situation is even more complicated. To demonstrate the complexity of the problem, we designed and applied simulations based on an extension of matrix models covering effects of propagule pressure and habitat limitation, and reflecting various characteristics of a species and of a habitat. These included life history, fecundity, seed bank viability of a species, habitat carrying capacity and disturbances. All the investigated factors affected proportion of occupied habitats. Whereas they can, to a large extent, compensate for each other, simultaneous decrease of habitat suitability and propagule input can be detrimental to the survival of a population. Our model demonstrated that in many cases, the absence of a species in a community is of stochastic nature, and result of interaction of species life history and various external conditions, and thus cannot be simply attributed to a single cause. The model results are supported with examples of case studies. The results also explain some well-known ecological phenomena, as decrease of niche breadth from the center to the margins of area of distribution. Finally, the model also suggests some caveats in interpretation of the results of sowing experiments.
Authors:P. Pech, J. Dolanský, R. Hrdlička, and J. Lepš
We examined the response of communities of four groups of organisms (plants, snails, ants and spiders) in a small scale mosaic of 8-years mown and unmown plots in a wet meadow in Central Europe. The experimental setup consisted of 7 unmown and 8 regularly mown 4 m2 plots in checkerboard arrangement. Eight years after the start of the experiment, the plant community structure diverged in response to mowing/nonmowing, both in species composition and structure. Both bryophyte and vascular plant species numbers were significantly higher in the mown plots. In unmown plots, bryophytes nearly disappeared and plots were dominated by the tall tussock grass Molinia caerulea. Both diversity and abundance of snails were higher in unmown plots than in mown ones. Ant nests were more abundant in mown plots and species composition differed between mown and unmown plots. We captured significantly more individuals of spiders in mown plots but we did not find any difference in species composition. We conclude that the 8-years duration of different management of 4 m2 plots was sufficient to establish different communities in low movable organisms, whereas these plots are probably too small to host different assemblages of organisms with good active dispersal abilities.
Authors:M. Dainese, M. Scotton, F. Clementel, A. Pecile, and J. Lepš
We studied the floristic composition in the pastures of the Southern Alps (Trento Province, Italy). One hundred and five plots in seven different pasture plant communities were sampled: (1) nitrophilous, (2) montane mesic, (3) subalpine mesic, (4) calcareous montane, (5) calcareous subalpine, (6) acid montane, and (7) acid subalpine pastures. Forward selection and variation partitioning were applied to identify the most important factors controlling the species composition and plant traits in the pastures. Aggregated weighted averages were calculated for each plot using the published values of average height, specific leaf area, and seed mass for each species. Explanatory variables were recorded for each site to reflect climate, soil properties, and grazing pressure. We hypothesised that species composition and functional variation in pastures of the Southern Alps are controlled by three main environmental filters: climate, resource availability, and grazing pressure. We found that variables of climate and soil properties had a major role in explaining the species composition and variations in plant traits, while grazing pressure showed a lower independent effect. Species composition and plant traits depended mainly on temperature, soil fertility, and variables of bedrock type — soil pH. Our results confirm the importance of taking the effects of climate and resource availability into account when describing plant and community functions of grasslands.
Authors:F. Bello, J. Lepš, S. Lavorel, and M. Moretti
Measurements of trait community composition are known to be sensitive to the way species abundance is assessed, but not to what extent. This was investigated by considering two of the most commonly used indices of community trait composition, trait averages and functional diversity, in bee communities along a post-fire environmental gradient. The indices were computed using three different species abundance measurements (log and unlog number of individuals and species occurrence only) and 5 traits. For certain traits, the responses of the indices to fire varied according to how species abundance was measured. The measurements that took species abundance into account in the most distinct way (e.g., occurrence vs. unlog data) produced the least similar results for all traits. Species were then grouped into different classes on the basis of their relative abundance (i.e., dominants, subdominants, and rare species). As a result, the measure that attaches the highest importance to the abundance of species (unlog data) related mostly to the dominant species traits, while the measure attaching the lowest (i.e., species occurrence) related more to rare species traits. Species diversity was mostly independent of trait averages and functional diversity, regardless of the measure of species abundance used. We also quantified functional redundancy (i.e., the potential minus the observed functional diversity in each community). When more weight was attached to species abundance, redundancy decreased and tended to be less correlated with species diversity. Overall, the way species abundance is taken into consideration in indices of functional composition offers promising insights into the way community assembly mechanisms respond to environmental changes.