Authors:Y. Zhang, K. Ma, M. Anand, W. Ye, and B. Fu
Alpha, beta, and gamma diversity are three fundamental biodiversity components in ecology, but most studies focus only on the scale issues of the alpha or gamma diversity component. The beta diversity component, which incorporates both alpha and gamma diversity components, is ideal for studying scale issues of diversity. We explore the scale dependency of beta diversity and scale relationship, both theoretically as well as by application to actual data sets. Our results showed that a power law exists for beta diversity-area (spatial grain or spatial extent) relationships, and that the parameters of the power law are dependent on the grain and extent for which the data are defined. Coarse grain size generates a steeper slope (scaling exponent z) with lower values of intercept (c), while a larger extent results in a reverse trend in both parameters. We also found that, for a given grain (with varying extent) or a given extent (with varying grain) the two parameters are themselves related by power laws. These findings are important because they are the first to simultaneously relate the various components of scale and diversity in a unified manner.
Local plant species richness and composition may vary across habitats and between plant taxonomic groups within temperate deciduous forests. Multi-taxon approach is therefore needed to provide a more detailed insight into determinants affecting vegetation structure. Fifty-four deciduous oak-dominated vegetation plots (20 m × 20 m) were sampled across central Slovakia (Štiavnické vrchy Mts) in order to study the effect of environmental (soil, light, topographic) factors on species richness and composition patterns of two main assemblages of understorey layer (herb-layer vascular plants and ground-dwelling bryophytes). The number of recorded herb-layer vascular plants and ground-dwelling bryophytes was 12–48 (mean 28) and 0–11 (mean 4) species per plot, respectively. Generalized linear model revealed that species richness of herb-layer vascular plants was driven by canopy openness, altitude, soil pH/base saturation gradient and plant-available phosphorus. Canopy openness and heat load index accompanied by soil pH/base saturation gradient determined changes of the ground-dwelling bryophyte richness. Canonical Correspondence Analysis identified soil pH/base saturation gradient, canopy openness, soil silt and topography related predictors (altitude, slope, radiation) as the main drivers of the herb-layer vascular plant compositional variability. Species composition variation of ground-dwelling bryophytes was controlled by radiation and canopy openness.
Authors:A. Gil-Tena, J. Nabucet, C. Mony, J. Abadie, S. Saura, A. Butet, F. Burel, and A. Ernoult
Over the last 30 years, ecological networks have been deployed to reduce global biodiversity loss by enhancing landscape connectivity. Bird species dwelling in woodland habitats that are embedded in agriculture-dominated landscapes are expected to be particularly sensitive to the loss of connectivity. This study aimed to determine the role of landscape connectivity in woodland bird species richness, abundance, and community similarity in north-east Brittany (north-west France). An exhaustive woodland selection protocol was carried out to minimize the effects of woodland size on the response variables. Connectivity of the woodland and forest network in the study area was evaluated using graph-theory, accounting for matrix permeability, and a characteristic median natal dispersal distance at the community level based on the bird species pool recorded in the sampled woodlands. Information-theoretic model selection, controlling for woodland size in all the cases, depicted the response of woodland birds at the community level to the connectivity of agriculture-dominated landscapes. On average, the sampled woodlands (n = 25) contained 15.5 ± 2.4 bird species, with an abundance of 25.1 ± 3.9, and had highly similar bird communities (species composition and proportion); eight species represented 57% of total abundance and were present in at least 22 woodlands. The performance of models improved when using effective, rather than Euclidean, interpatch distances in the connectivity assessment. Landscape connectivity was only significantly related to similarity of proportional species composition. Large woodlands contained communities with more similar species proportions in an inhospitable agricultural landscape matrix than in a more permeable one. Woodland size was the most relevant factor determining species abundance, indicating that the bird population sizes are primarily proportional to the local habitat availability. Connectivity in relation to landscape matrix permeability did not seem to induce the flow of woodland-dependent bird species that are dominant in the community but rather of matrix-dwelling bird species that are less dependent on woodland patch area. In conclusion, both habitat conservation and restoration (i.e., amount and quality), in combination with permeable landscape structures (such as heterogeneous land cover mosaics), are advocated for community level conservation strategies.
After stressing the need to keep separated the concept of variability and/or inequality and dissimilarity from that of diversity, it is suggested that diversity of a system should be measured primarily by the number of different classes (K) we can define in it (richness) by classification or identification processes. An index d, ranging between 0 and 1, that summarizes the similarity pattern within the system, can be used if necessary to transform K to a “fuzzy” diversity number, according to the idea that the higher is the similarity within the system the lower should be its diversity. Another index, r, is proposed to measure the “loss” of diversity due to similarity within the system, an index that fits the concept of “redundancy”. Since every diversity vector may be interpreted as a crisp symmetric similarity matrix, of which the Gini-Simpson’s index is the average dissimilarity, while the index of Shannon is the entropy of its eigenvalues, the index d can be chosen to quantify one among the following similarities: a) the overall average similarity of the classes considering the within classes similarity equal to 1 and the between classes similarity equal to 0 (crisp similarity pattern): this is coincident with the evenness of the proportion of importance of the classes, b) the average similarity between the classes without considering evenness, or c) the combination of the two similarities (similarity between the classes and evenness). In these last two cases, the similarity between the classes is characterizing the similarity pattern of a system in a fuzzy way (fuzzy diversity). It is stressed that the diversity of vegetation systems may be of two complementary types: plant individual-based diversity and plant community-based diversity. If we assume that each plant community type corresponds to one habitat then habitat diversity (or niche width) can be calculated for each class of plant individuals according to the number of classes of plant communities in which we can find it. Habitat diversity can be used to measure the indicator value of species or other classes of plant individuals and of plant communities. In this last case, we have to consider the distribution of plant communities in classes defined by environmental factors. It is suggested that the terminology alpha, beta, gamma diversity can be useful only if used to distinguish types of diversity in vegetation systems: alpha diversity = plant individual based diversity, gamma diversity = the union of alpha diversities, beta diversity = plant community based diversity. Thanks to the availability of mathematical tools, it is concluded that rather than being worried about measuring diversity it would be more fruitful to worry about why we are willing to measure it.
Authors:R. E. Lorenzón, A. H. Beltzer, P. M. Peltzer, A. L. Ronchi-Virgolini, M. Tittarelli, and P. Olguin
We studied spatial changes in species composition (i.e., beta diversity) of local assemblages of birds along ∼450 km of the Middle Paraná River, an extensive fluvial system of South America. Point counts were used to survey birds at 60 plots located in shrub swamps and marshes of the floodplain within four sites (15 plots per site). Two sites were surrounded by each of the two upland ecoregions. Beta diversity of bird assemblages was high and was more important than alpha diversity in shaping regional diversity (i.e., gamma diversity) of the fluvial system. Compositional changes were related to species turnover among plots, while nestedness dissimilarity was not important for shaping diversity patterns. Variation-partitioning analysis showed that local conditions (i.e., landscape composition within a radius of 200 m from the center of each plot) accounted for more spatial variation in assemblage composition than did location along the fluvial system. Adjacent upland ecoregions did not account for spatial changes in bird composition within the fluvial system. In conclusion, environmental heterogeneity created by flood pulses is an important factor for sustaining regional diversity of birds within the fluvial system through effects on beta diversity.
Authors:M. Zeidler, M. Duchoslav, M. Banaš, and M. Lešková
Dwarf pine (Pinus mugo) is a successful pioneer tree, but also an invader of the subalpine belt in Central-European mountains. In the Hrubý Jeseník Mts. (Czech Republic), dwarf pine was introduced at the end of the 19th century by humans into alpine communities. To analyse the influence of non-native woody species on species diversity, vegetation composition and the ecological bioindication of invaded alpine communities, three habitats (non-invaded alpine grasslands, gaps of alpine grasslands within dwarf pine stands and closed dwarf pine stands) were compared at two localities (Keprník, Tabulové kameny) using the space-for-time substitution approach. Plant species composition was assessed by means of phytosociological relevés, and bioindication by means of Ellenberg indicator values. At both localities, both beta and gamma diversity were lower, and species composition more uniform in dwarf pine plantations in contrast to the gaps within and alpine grasslands outside of dwarf pine stands. At Keprník, alpha diversity was lower in the dwarf-pine plantation than outside of it, while at Tabulové kameny no significant differences were found. This is probably due to the somewhat different spatial structure of the dwarf pine stands and the different timing of dwarf pine introduction at these localities. Bioindication showed that dwarf-pine stands were drier, more shaded and had a higher soil fertility than alpine grasslands. Dwarf pine colonisation of alpine grasslands causes the extinction of many endangered plant species, complicating conservation goals. Because of the limited size of alpine areas, changes caused by dwarf pine in medium-high mountains might be more significant than in mountains with large alpine forest-free areas.
Authors:L. Grandpré, D. Boucher, Y. Bergeron, and D. Gagnon
Boreal mixedwood understory communities are highly dynamic because they are simultaneously influenced by canopy succession, small-scale environmental variation and disturbances. In such a system, fire initiates succession but canopy gaps, resulting from spruce budworm outbreaks or other disturbances, also affect forest dynamics during succession. In this study, we assessed the short-term response of understory communities along a canopy gap severity gradient in mature and old-growth forest stands. The objective was to determine if resource heterogeneity is driving understory community composition and diversity. We created artificial gaps of varying severities in stands of two late successional forest stages. Four treatments, i.e., total cut, conifer cut, girdling of conifers and a control treatment, were each applied over an area of 100 m2 and replicated three times in both types of forest stands. The cover of each understory species was measured before treatment application and 1, 2 and 11 years following it, in seven 1 m2 plots per replicate. Percent transmission of photosynthetic photon flux density and soil temperature were also measured on different occasions after the beginning of the experiment. Species richness, alpha diversity and total cover all increased following gap creation, and this increase was sustained up to 11 years. Increases were more pronounced in total cut than in other treatments. The increase in species richness and diversity was also more pronounced in old-growth stands, while total cover increase was greater in mature stands. Gap creation resulted in significant changes in abundance patterns that were associated with the resident species assemblages. The magnitude of changes in community composition did not significantly differ between mature and old-growth forests and differences in species composition among stands were maintained following gap creation. This study supports the evidence that resource heterogeneity resulting from small-scale disturbances will contribute to maintaining diversity among understory communities by allowing species more typical of early-successional communities to coexist with species from late-successional ones. Such a process may be essential for maintaining the species pool likely to re-invade the stands following major disturbances.
Authors:R. Ohlemüller, P. Bannister, K.J.M. Dickinson, S. Walker, B.J. Anderson, and J.B. Wilson
.D. Clarkson. 1998. Environmental correlates of tree alpha-diversity in New Zealand primary forests. Ecography 21: 235-246.
Environmental correlates of tree alpha-diversity in New Zealand primary forests