Self-similarity and the species-area relationship

Self-similar distributions of species across a landscape have been proposed as one potential cause of the well-known species-area relationship. The best known of these proposals is in the form of a probability rule for species occurrence. The application of this rule to the number of species occurring in primary well-shaped rectangles within the landscape gives rise to a discrete power law for species-area relationships. However, this result requires a specific scheme for bisecting the landscape to generate the rectangles. Some additional, more general consequences of the probability rule are presented here. These include the result that the number of species in a well-shaped rectangle depends on its location, not just on its area. In addition, a self-similar landscape contains well-shaped rectangles that are, in fact, not self-similar. The probability rule in general produces testable predictions about how and where species are distributed that are independent of the power law.     

History and the species-area relationship in Lesser Antillean birds

We examined the species-area relationship for three historically distinct subsets of Lesser Antillean birds identified by molecular phylogenetic analysis of island and continental populations. The groups comprised recent colonists from continental or Greater Antillean source populations, old taxa having recently expanded distributions within the Lesser Antilles, and old endemic taxa lacking evidence of recent dispersal between islands. The number of young taxa was primarily related to distance from the source of colonists in South America. In a multiple regression, the logarithmic slope of the species-area relationship for this group was shallow (0.066+/-0.016). Old endemic taxa were restricted to islands with high elevation, and within this subset, species richness was related primarily to island area, with a steep slope (0.719+/-0.110). The number of recently spread endemic taxa was related primarily to island elevation, apparently reflecting the persistence of such populations on islands with large areas of forested and montane habitats. Historical analysis of the Lesser Antillean avifauna supports the dynamic concept of island biogeography of MacArthur and Wilson, rather than the more static view of David Lack, in that colonists exhibit dispersal limitation and extinction plays a role in shaping patterns of diversity. However, the avifauna of the Lesser Antilles is probably not in equilibrium at present, and the overall species-area relationship might reflect changing proportions of historically distinguishable subsets of species.     

The species-area relationship of European Lumbricidae (Annelida,Oligochaeta)

Summary Studies throughout Europe reporting species lists of lumbricid earthworms and ranging from 100 m² to >500000 km² are analysed for the regression of species number S on size of area A [km²]. This species-area relation is described by: S=7.9*A^0.09 (r=0.76).Revised version of a poster presented at the Wilhelm Michaelsen Memorial Symposium (International Symposium on Terrestrial Oligochaeta), Hamburg Sept. 14–18th 1987     

Local richness-species pool ratio: A consequence of the species-area relationship

A constant ratio between species richness estimated at the local and regional scale is interpreted as a proof of quasi-neutral unsaturated communities. Based on Zobel’s model of plant community (Zobel,Folia Geobot. 36: 3–8, 2001) we tested the methodology of the species-pool concept by comparing the saturated and unsaturated communities generated by spatially-explicit mechanistic simulations with known assembly rules. Tests show that local-regional species plots can be applied to distinguish saturated vs. unsaturated communities, however, the outcome of tests, i.e. the relationship between local and regional richness depends on the size of the areas compared. Independently from the mechanisms controlling diversity, trivial saturation will appear if one of the scales is either too small or too broad because species-area curves are bound at these extreme scales. Similarly, trivial unsaturaton will appear if the two scales compared are close to each other. The application of species-area curves is useful because they help to find scales for non-trivial relationships. Field tests reporting quasi-neutrality and unsaturated plant communities were performed at the intermediate scales of the corresponding species-area curves, and they were estimated from heterogeneous samples. Therefore, this field evidence might be biased by scaling artefacts. We propose to reanalyze the field evidence with solid scaling conventions and to restrict the concept of quasi-neutrality to subordinated functional groups based on the following hypotheses: (1) neutrality will appear within subordinated guilds as a consequence of the hierarchical structure of plant communities; (2) the lower a guild in the hierarchy the higher neutrality of within-layer processes detected; (3) quasi-neutrality found at the community level is not a proof of community-level neutrality but it is due to the higher number of subordinated species in the samples.     

Between geometry and biology: the problem of universality of the species-area relationship

The species-area relationship (SAR) is considered to be one of a few generalities in ecology, yet a universal model of its shape and slope has remained elusive. Recently, Harte et al. argued that the slope of the SAR for a given area is driven by a single parameter, the ratio between total number of individuals and number of species (i.e., the mean population size across species at a given scale). We provide a geometric interpretation of this dependence. At the same time, however, we show that this dependence cannot be universal across taxa: if it holds for a taxon composed from two subsets of species and also for one of its subsets, it cannot simultaneously hold for the other subset. Using three data sets, we show that the slope of the SAR considerably varies around the prediction. We estimate the limits of this variation by using geometric considerations, providing a theory based on species spatial turnover at different scales. We argue that the SAR cannot be strictly universal, but its slope at each particular scale varies within the constraints given by species' spatial turnover at finer spatial scales, and this variation is biologically informative.     

Effect of community assembly and primary succession on the species-area relationship in disturbed ecosystems

The species-area relationship (SAR) provides a cornerstone for ecological theory. Implicit in SAR studies is the assumption that SAR properties, especially SAR slopes, remain constant through time, even though the ecosystem characteristics that they encompass–the spatial distribution and abundance of species–change on seasonal to evolutionary time scales. Focusing on disturbed subalpine systems, we evaluated whether SAR properties are a function of stage of succession at Mount St. Helens, WA, and at Gothic, CO. We found that the SAR flattens and shifts upward as these systems mature. The decrease in SAR curvature at Mount St. Helens suggests a transition toward power-law SAR behavior with assembly. Overall, the observed changes in SAR properties raise questions about the appropriateness of applying contemporary SARs to predict future levels of species richness in disturbed or successional systems.     

Predator-dependent species-area relationships

In addition to having a positive effect on species richness (species-area relationships [SARs]), habitat area can influence the presence of predators, which can indirectly influence prey richness. While these direct and indirect effects of area on richness occur simultaneously, no research has examined how predation might contribute to SAR variation. We extend MacArthur and Wilson's equilibrium theory of island biogeography by including predation-induced shifts in prey extinction and predict that predators will reduce slopes of prey SARs. We provide support for this with data from two insular ecosystems: orthopteran richness in Ozark glades (rocky herbaceous communities within a forested matrix) with and without insectivorous lizards and zooplankton richness in freshwater ponds with and without zooplanktivorous fishes. Our results emphasize that anthropogenic activities yield simultaneous changes in processes altering diversity and that it is critical that we understand how these components of anthropogenic change interact to impact diversity.     

Breakdown of the species-area relationship in exotic but not in native forest patches

We studied the pattern of bird species richness in native and exotic forest patches in Hungary. We hypothesized that species-area relationship will depend on forest naturalness, and on the habitat specialization of bird species. Therefore, we expected strong species-area relationship in native forest patches and forest bird species, and weaker relationship in exotic forest patches containing generalist species. We censused breeding passerine bird communities three times in 13 forest patches with only native tree species, and 14 with only exotic trees in Eastern Hungary in 2003. Although most bird species (92%) of the total of 41 species occurred in both exotic and native forests, the species-area relationship was significant for forest specialist, but not for generalist species in the native forests. No relationship between bird species and area was found for either species group in the forest with exotic tree species. The comparison of native versus exotic forest patches of similar sizes revealed that only large (>100 ha) native forests harbor higher bird species richness than exotic forests for the forest specialist bird species. There is no difference between small and medium forest patches and in richness of generalist species. Thus, the species-area relationship may diminish in archipelago of exotic habitat patches and/or for habitat generalist species; this result supports the warning that the extension of exotic habitats have been significantly contributing to the decline of natural community patterns.     

Effects of patch size on colonisation in estuaries: revisiting the species-area relationship

The effects of patch size on the colonisation and succession of intertidal invertebrates and algae were investigated in an estuary near Sydney, New South Wales, Australia. The specific aim was to test explicitly for the presence of a species-area relationship, and examine whether this could be explained by the random placement hypothesis (i.e. that the number of species per unit area was the same on patches of different sizes). In addition, I tested the extent to which differences in numbers of species reflected differences in the composition of assemblages. Wooden panels of three different sizes (10 × 10 cm, 20 × 20 cm and 40 × 40 cm) were placed in the field on intertidal oyster leases in each of two different experimental trials: spring (October 1994) and summer (January 1995). Independent replicate measures of the number of colonising species on panels were obtained after different periods of time, up to 25 months. I also obtained measures of abundance of individual species and composition of assemblages on panels of different sizes. This allowed specific tests of the hypothesis that the size of the patch being colonised is important in structuring these assemblages. The strength of the species-area relationship increased through time on panels submersed in October, but the trend was reversed for panels submersed in January. There was a significant interaction between factors of patch size and time of submersion for multivariate measures of differences in composition among replicates. The random placement hypothesis was supported in certain situations, but not in others. When rejected, it was for different reasons on panels submersed in the two different trials. Panels initiated in October tended to have proportionally greater numbers of species per unit area on larger panels, while the panels initiated in January tended to have more species per unit area on smaller panels. There was an identifiable relationship between differences in numbers of species and differences in species composition for panels submersed in October. This was not true, however, for panels submersed in January, where the species-area relationship did not hold after longer periods. The succession of organisms through time was, overall, more important in structuring the assemblages than was the size of the patch being colonised. The species-area relationship should not necessarily be regarded as a truism – it did not always hold in this system. The initial timing of experiments with respect to recruitment and succession influenced the results. Received: 16 March 1998 / Accepted: 5 October 1998     

Scale-dependence in species-area relationships

Species-area relationships (SARs) are among the most studied phenomena in ecology, and are important both to our basic understanding of biodiversity and to improving our ability to conserve it. But despite many advances to date, our knowledge of how various factors contribute to SARs is limited, searches for single causal factors are often inconclusive, and true predictive power remains elusive. We believe that progress in these areas has been impeded by 1) an emphasis on single-factor approaches and thinking of factors underlying SARs as mutually exclusive hypotheses rather than potentially interacting processes, and 2) failure to place SAR-generating factors in a scale-dependent framework. We here review mathematical, ecological, and evolutionary factors contributing to species-area relationships, synthesizing major hypotheses from the literature in a scale-dependent context. We then highlight new research directions and unanswered questions raised by this scale-dependent synthesis.     

河南宝天曼落叶阔叶林木本植物单物种–面积关系

单物种–面积关系(ISAR)方法可判定单个物种在不同空间尺度下对邻域生物多样性的影响作用是促进、抑制或中性。尽管已有研究尝试分析了不同径级大小个体对邻域植物多样性的影响,但这方面仍缺乏较系统的研究,对不同径级植株在维持森林群落植物多样性方面的作用差异仍不清楚。本研究以河南宝天曼国家级自然保护区1ha落叶阔叶林固定样地为例,通过对全部树(包括大树和小树)分别对全部树/大树/小树,大树分别对全部树/大树/小树,小树分别对全部树/大树/小树9种类型的ISAR进行比较分析,拟验证如下假设:(1)大树相比小树来说对邻域植物多样性的影响更大,(2)同一物种或同一径级个体对邻域小树比对邻域大树的影响要强,(3)宝天曼落叶阔叶林木本植物中中性物种占主体。结果显示不同大小的树木个体对邻域植物多样性的影响作用也因空间尺度、邻域植物个体大小而有所差别:支持同一物种或同一径级个体对邻域小树比对邻域大树的影响要强的假设,没有检测到大树比小树对邻域植物多样性更大的影响作用;中性物种在所研究森林群落中1–10 m尺度上均占绝对优势,促进种的数量在全部树对全部树,全部树对小树,小树对全部树以及小树对小树情况下随着尺度的增加呈先升高后下降的趋势,抑制种在少数小尺度下被少量检测到。本研究结果有助于我们更好地认识和理解森林群落中物种作用及群落维持机制,但该结果还需在更大尺度样地以及其他类型的森林中进行检验。     

The species-area relationship in the hoverfly (Diptera, Syrphidae) communities of forest fragments in southern France

The effect of forest fragmentation was studied in hoverfly communities of 54 isolated forests (0.14–171 ha) in south west France. The positive relationship between species richness and wood patch area was investigated by testing the three hypotheses usually put forward to explain it: 1) the sampling effect hypothesis, 2) the patch heterogeneity hypothesis, 3) the hypothesis of equilibrium between distance from other patch (colonisation) and surface area of the patch (extinction). The syrphid species were divided into 3 ecological groups, based on larval biology as summarized in the "Syrph the Net" database: non forest species, facultative forest species and forest species. A total of 3317 adults belonging to 100 species, were captured in the 86 Malaise traps. Eight species were non forest (N=16), 65 facultative forest (N=2803) and 27 forest species (N=498).
Comparison of the slopes of the species-area curves for species richness and species density per forest patch showed a strong sampling effect in the species-area relationship. Wood patch heterogeneity increased with wood patch area and positively influenced hoverflies richness. Less isolated wood patches presented high richness of forest species and low richness of non forest species. Only forest species richness seemed to respond to the equilibrium between surface area and isolation. Depending on which hypothesis explained best the species-area relationship, management recommendations to mitigate fragmentation effects were formulated at various spatial scales and for different stakeholders.     

动物进化中神经肽样物质和神经系统关系之探讨

用免疫组织化学方法,研究和追踪神经肽样物质在原生动物、水螅及蝾螈胚胎发育过程中分布的变化,试图探索在动物早期进化过程中神经肽样物质和神经系统之间的关系。实验结果表明：（1）从系统发育看神经肽样物质比神经系统先出现并行使在细胞内的功能。（2）在随后的进化中神经肽样物质先分布于非神经系统部位,如肠道外缘及表皮,并逐渐进入神经系统,这无论从系统发育和个体发育中都能找到依据。（3）在神经系统,神经肽样物质先出现在周边神经,之后;才出现在中枢神经,实验中表明NPY是随着神经嵴细胞的迁移而进入周边神经系统,之后,随着胶质细胞的出现而出现在中枢神经系统。（4）原生动物和蝾螈胚胎均由皮膜或表皮细胞中囊泡状结构直接分泌神经肽祥物质进入胞质内或细胞外。     

Linking species-area and species-energy relationships in Drosophila microcosms

Resource availability is an important constraint on community structure. Some authors have suggested it conceptually links two of the most basic patterns in ecology, the species–area relationship and the latitudinal gradient in species richness. I present the first experimental test of this conjecture, by manipulating both the area and resource concentration of artificial larval drosophilid fly habitats and then allowing colonization from a natural species pool. Both the abundance and species richness of these habitats depended upon the total quantity of resources available, regardless of whether those resources were contained within smaller high-quality habitats or larger poor-quality habitats. While the intercepts of species–area relationships varied with resource concentration, they all collapsed onto the same species–energy curve. These results support the view that energetic constraints are of fundamental importance in structuring ecological communities, and that such constraints may even help explain ecological patterns such as the species–area relationship that do not explicitly address resource availability.     

Evaluation of species-area functions using Sonoran Desert plant data: not all species-area curves are power functions

Ecologists have been studying the relationship between species richness and area for about a century. As area increases, more species are typically observed. Many mathematical functions have been proposed to describe the pattern of increase. Numerous researchers have assumed that the relationship is a power function despite the fact that there are many possible alternatives. There has been limited work in evaluating which species-area functions are most appropriate for field data. This study examines which of a variety of functions best describe how Sonoran Desert plant species richness of remnant habitat patches in the Phoenix metropolitan area vary with sampled area and the area of entire patches. No single species-area function was adequate for describing all empirical datasets. Sample curves of woody species were most frequently best described by the sigmoid logistic, Hill, and Lomolino functions, whereas herbaceous datasets were best fit by the sigmoid logistic or convex rational functions. A curve depicting the relationship between patch-level woody species richness and patch area was best fit by the convex exponential function. The power function provided the best fit for only one case. This study demonstrates the utility of testing alternative functions for statistical fit rather than assuming that any particular equation adequately describes the species-area relationship.