Cumulative Species Richness Research Articles

Short-term effect of windstorm disturbance on saproxylic beetles in broadleaved temperate forests: Part II. Effects of gap size and gap isolation

The short-term effect of windthrow gap size and isolation for saproxylic beetle abundance, species richness and assemblage composition was studied in managed oak-hornbeam forest in France. The main gap effects did not increase with gap area. Non-metric multi-dimensional scaling (NMDS) and ANOSIM tests showed that all gaps, even small, differed from closed-canopy controls in terms of saproxylic species composition. However, only mid-size gaps were distinct from large and especially small gaps. The highest Bray–Curtis dissimilarity occurred between mid-size gaps and closed-canopy controls, and not between large gaps and controls. Partly in agreement with the resource concentration hypothesis, floricolous beetles were more abundant in mid-size and large gaps than in small ones. However, pioneer xylophagous species did not increase and late-successional xylophagous species did not decrease in abundance with increasing gap area. A peak in cumulative and mean local species richness was measured in mid-size gaps, but assemblage composition in mid-size gaps was not intermediate between small and large gaps, which does not fully comply with the intermediate disturbance hypothesis. From IndVal results, no strictly characteristic species were detected in small gaps, but several ones in mid-sized and large gaps. On the whole, scolytids and pioneer xylophagous beetles were favoured in gaps by an increase in felling density in the 78 and 314 ha surrounding landscapes, respectively. Individual species responses in occurrence or abundance were varied. As the faunistic peculiarity in the gaps was mainly confined to mid- and large-sized gaps, retaining uncleared gaps above 0.5 ha in size is recommended to improve saproxylic gamma diversity in forests.

Crustacean zooplankton in lakes and reservoirs of temperate and tropical regions: variation with trophic status

The influence of trophic status on the crustacean zooplankton community was investigated in lakes and reservoirs in temperate and subtropical-tropical regions. We tested if there is a consistent relationship between crustacean species richness, assemblages, and abundance and trophic indices such as total phosphorus and chlorophyll a. We also examined if these patterns differ between regions. Cumulative species richness and assemblages varied among regions. The greatest number of crustacean species was found in the temperate oligotrophic region with the largest number of lakes sampled. However, cumulative species richness was similar in temperate and subtropical–tropical regions when comparing subsets with a similar number of lakes and reservoirs. The relationships between species richness and latitude or trophic status were difficult to assess owing to imbalance among regions in number of lakes and reservoirs sampled and to biogeography and fish predation potential influences. Trophic status was associated with changes in abundance of all major crustacean zooplankton groups. Eutrophic ecosystems supported greater crustacean abundances at all latitudes. However, cladocerans and cyclopoids were more abundant in eutrophic lakes and reservoirs, whereas calanoids were more abundant in temperate oligotrophic lakes. Total phosphorus was found to be a better predictor of the biomass of major crustacean groups than chlorophyll a in all regions.

Fungal diversity during initial stages of leaf decomposition in a stream

Maple, linden and oak leaves were immersed in a stream for 1-21 d. Cumulative mass loss, ergosterol content, and species richness of released aquatic hyphomycete conidia increased with time. Numbers and richness of attached conidia were highest on days 1 and 2. Denaturing gradient gel electrophoresis revealed up to seven fungal phylotypes on the leaves before their immersion in the stream and after one day of stream exposure. After 5 d of immersion the contribution of these terrestrial fungi decreased and that of aquatic hyphomycetes increased. The dominant phylotypes belonged to Anguillispora filiformis, Articulospora tetracladia and Flagellospora curvula, which also dominated the community of released spores. The molecular diversity was highest on day 2 and 3 on all substrates. This may be due to a few species of terrestrial fungi, later outcompeted by aquatic hyphomycetes, and to many different conidia of aquatic hyphomycetes, some of which may germinate but are unable to establish themselves and reproduce.

Parasitological analyses of the male chimpanzees (Pan troglodytes schweinfurthii) at Ngogo, Kibale National Park, Uganda

Numerous intestinal parasites identified in populations of wild nonhuman primates can be pathogenic to humans. Furthermore, nonhuman primates are susceptible to a variety of human pathogens. Because of increasing human encroachment into previously nonimpacted forests, and the potential for disease transmission between human and nonhuman primate populations, further detailed investigations of primate ecological parasitology are warranted. For meaningful comparisons to be made, it is important for methods to be standardized across study sites. One aspect of methodological standardization is providing reliable estimates of parasite prevalence and knowing how many samples are needed to adequately estimate an individual's parasite prevalence. In this study the parasitic fauna of 37 adult, adolescent, and juvenile male chimpanzees from the Ngogo group, Kibale National Park, Uganda, were assessed from 121 fecal samples collected over a 3-month period. Twelve taxa of intestinal species (five helminth and seven protozoan) were recovered from the samples. The four most prevalent species were Troglodytella abrassarti (97.3%), Oesophagostomum sp. (81.1%), Strongyloides sp. (83.8%), and Entamoeba chattoni (70.3%). No one species was found in all samples from any one animal, and Troglodytella abrassarti, the most common intestinal organism, was found in all of the serial samples of only 69.4% of the chimpanzees. The cumulative species richness for individuals significantly increased for every sequential sample (up to three to four samples) taken per animal during this study. The results indicate that to accurately diagnose total intestinal infection and evaluate group prevalence, three to four sequential samples from each individual must be collected on nonconsecutive days. This conclusion applies only to short study periods in which possible seasonal effects are not taken into consideration. Validation of these results at different study sites in different regions with different climatic patterns is needed.

Uncommon bryophytes in Swedish forests?key habitats and production forests compared

An ongoing large-scale survey has revealed that there are 60–70 000 ‘woodland key habitats’ in Sweden, covering at least 1% of the productive forestland. According to definition they should contain red-listed species, but no inventories of these species have been made and instead the survey has been based on indirect criteria like natural forest characteristics and indicator species. We compared red-listed and indicator bryophytes between woodland key habitats (WKHs) and production forests (PFs) in two areas (500 and 600 km2) in south-east Sweden, using randomized sampling and with line-transect analysis. The number of records per hectare (one record=presence in a 10m×10 m) of red-listed bryophytes in the WKHs was 0.4 and 4, and in the PFs 0.5 and 0.8, depending on area. In only one of the areas, did WKHs have significantly more records per hectare and a larger number of red-listed bryophyte species log ha−1 than the PFs. The cumulative species richness for indicator species and red-listed species together was significantly higher in WKHs compared with PFs in both areas, to judge from the confidence bands of species accumulation curves. Positive correlations between red-listed species and indicator species regarding their number as well as their abundance in the WKHs support the use and selection of indicator species. Our results show that WKHs do not necessarily have a higher density of red-listed bryophyte species than PFs, especially when compared with mature PFs. A more complete picture would be achieved if different forest types and age classes were investigated separately, in a replicated design.

Uncommon bryophytes in Swedish forests—key habitats and production forests compared

An ongoing large-scale survey has revealed that there are 60–70 000 ‘woodland key habitats’ in Sweden, covering at least 1% of the productive forestland. According to definition they should contain red-listed species, but no inventories of these species have been made and instead the survey has been based on indirect criteria like natural forest characteristics and indicator species. We compared red-listed and indicator bryophytes between woodland key habitats (WKHs) and production forests (PFs) in two areas (500 and 600 km 2) in south-east Sweden, using randomized sampling and with line-transect analysis. The number of records per hectare (one record=presence in a 10 m×10 m) of red-listed bryophytes in the WKHs was 0.4 and 4, and in the PFs 0.5 and 0.8, depending on area. In only one of the areas, did WKHs have significantly more records per hectare and a larger number of red-listed bryophyte species log ha −1 than the PFs. The cumulative species richness for indicator species and red-listed species together was significantly higher in WKHs compared with PFs in both areas, to judge from the confidence bands of species accumulation curves. Positive correlations between red-listed species and indicator species regarding their number as well as their abundance in the WKHs support the use and selection of indicator species. Our results show that WKHs do not necessarily have a higher density of red-listed bryophyte species than PFs, especially when compared with mature PFs. A more complete picture would be achieved if different forest types and age classes were investigated separately, in a replicated design.

Species richness of moss landscapes unaffected by short‐term fragmentation

Theory predicts that habitat fragmentation and varying corridor length and width will affect animal populations in adjoining habitat patches due to varying migration rates. Previous work on the moss/microarthropod microcosm showed that connecting moss patches with moss corridors maintained species richness and individual species abundance. By contrast, in this study there was little evidence for differences in species richness between landscapes of varying connectivity and corridor length and width. The γ diversity, the cumulative species richness of entire connected systems, followed the same pattern. Similar non‐significant results were obtained for species abundance. Contrary to a previous study, I found no evidence that populations of predators were more affected by fragmentation than non‐predators. Since this experiment ran during temperate environmental conditions and the previous experiments ran during more extreme conditions, I hypothesise that corridors may be more useful in reducing species extinction during extreme environmental conditions.

ECOSYSTEM ENGINEERING BY CATERPILLARS INCREASES INSECT HERBIVORE DIVERSITY ON WHITE OAK

By creating or modifying habitats used by other organisms, physical ecosystem engineers can influence local patterns of biological diversity. However, there have been very few empirical studies quantifying engineering effects in different biological systems. In this study, we examined the effect of shelter-building caterpillars on the species richness and guild structure of leaf-chewing herbivores occupying individual white oak (Quercus alba) saplings. For each of two years, we disrupted leaf-tie formation on 93 white oak saplings during a three-week period in early summer that coincided with the peak in leaf-tie construction by the most common leaf-tying caterpillar, Pseudotelphusa sp. (Gelechiidae). We then created artificial leaf ties on 62 of these saplings by clipping together adjacent pairs of leaves (10% of the foliage) on each tree. For 31 of these trees, we also placed a single Pseudotelphusa caterpillar into each artificial tie to examine possible nonengineering effects associated with the caterpillar in addition to its shelter-building activity. One month later, removal of leaf ties had reduced the average density of leaf ties present on a tree by 61% (1999) and 54% (2000). This effect persisted throughout the season, indicating that no species assumed the engineering role of Pseudotelphusa sp. once it was removed. The decrease in shelter availability significantly decreased mean cumulative species richness of leaf-chewing insects by 38% (1999) and 14% (2000) compared to the two artificial tie treatments (with and without caterpillars initially), which did not differ from one another. Herbivore community composition also differed significantly between the removal and artificial tie treatments in both years, due to increased species richness of leaf-tying caterpillars (1999 and 2000), sawflies (1999 only), and beetles (2000 only) on trees with artificial ties. By creating leaf shelters early in the season, Pseudotelphusa sp. caterpillars have large and persistent effects on seasonal patterns of herbivore recruitment to and/or retention by white oak trees. Corresponding Editor: R. F. Denno

Ciliate populations in temporary freshwater ponds: seasonal dynamics and influential factors.

SUMMARY 1. The ciliate populations of two temporary ponds in southern Ontario were studied throughout their aquatic phases in 2001. Pond I (∼1 ha) held water for 98 days, whereas Pond II (∼0.25 ha) held water for 34 days. Populations were assessed both within the ponds themselves and within a series of enclosures in which invertebrate predator pressure was manipulated.2. In the natural pond water, total ciliate abundance in Pond II rose rapidly from day 1 increasing two orders of magnitude by day 7. In contrast, total abundance in Pond I began at the same level as in Pond II but increased much more slowly, reached a plateau of around 500 individuals L−1, and increased again late in the hydroperiod.3. Despite being only 500 m apart, the two ponds were fairly dissimilar in terms of their species richness and species composition. Pond I contained 50 species compared with 70 species for Pond II, with only 24 species shared. Additional species occurred within the enclosures raising the total species richness to 145 species; 88 from Pond I, 104 from Pond II, with 47 species (30%) in common. Pond II contained more mid‐sized ciliates (50–200 μm), whereas Pond I was dominated by smaller ciliates, especially in mid‐May and early June. In Pond I, cumulative species richness throughout the hydroperiod was highest in the predator addition enclosures (65 ± 4 species), followed by the partial‐predator exclusion enclosures (50 ± 4). Lowest species richness was found in the control enclosures (39 ± 2) and in the pondwater controls (39 ± 0). Differences between the ciliates in the natural pond water and the enclosures appeared to be related to a greater concentration of phytoplankton within the enclosures (perhaps resulting from extensive growth of duckweed, Lemna, outside), and higher densities of zooplankters in the pond.4. The physicochemical environment influenced species richness, total abundance and the number of rare species (27 in Pond II versus 13 in Pond I). Variation in ciliate abundance in Pond I could be explained by the number of days after filling (39%) and enclosure treatment (23%). These two parameters also explained 72% of the variation in species richness in Pond I (46 and 26%, respectively). Sixty‐five per cent of the variation in abundance in Pond II could be explained by the measured parameters: number of days after filling 27%, pH 19%, and nitrate levels 12%. Fifty‐two per cent of the variation in species richness was explained by the environmental parameters, of which pH was the most influential. Species succession was a strong feature of both ponds and its relationship to environmental variables and the presence of other organisms is discussed.5. Addition of invertebrate predators resulted in higher abundance and higher species richness for a limited time period in one of the ponds – suggesting that differences in foodweb dynamics may influence ciliate community composition.

An investigation into the metazoan parasites of the spiny dogfish (Squalus acanthias L.), off the west coast of Ireland

The present study was undertaken to examine the parasite fauna of spiny dogfish, and to determine seasonal variations in infection rates and faunal composition. A total of 10 metazoan parasite species was recorded, of which four species occurred in the intestine, three species were parasitic on the gills, two species occurred on the skin, and one species parasitized the spiracle. However, a cumulative parasite species richness curve indicated that a larger sample may have yielded additional parasite species. The parasite assemblage consisted of five species of copepods (Eudactylina acanthii Scott, Caligus curtis Müller, Pandarus bicolor Leach, Echthrogaleus coleoptratus (Guerin-Meneville) and Pseudocharopinus bicaudatus (Krøyer)), two species of nematodes (Anisakis simplex Rudolphi and Hysterothylacium aduncum (Rudolphi)), two species of cestodes (Trilocularia gracilis Olssen and Gilguina squali (Fabricius)), and one species of monogenean (Erpocotyle abbreviata (Olssen)). The parasite fauna was found to be similar to that of S. acanthias from the North Sea, and from New Zealand waters. Results obtained during the present study indicate that the infection rates of certain parasite species display seasonal cycles, most species displaying their greatest prevalence in spring and their lowest prevalence in autumn.

Effects of catchment perturbations by logging and wildfires on zooplankton species richness and composition in Boreal Shield lakes

SUMMARY 1. Forest logging and wildfires are important perturbations of the boreal forest, but their effects on lake biota remain largely unknown. Here, we test whether zooplankton species richness and species assemblages differed among three groups of lakes in Eastern Canada characterised by different catchment conditions: logged in 1995 (n=9); burnt in 1995 (n=9); unperturbed (n=20). Lakes were sampled in June, July and September 1 year after catchment perturbations.2. Cumulative species richness in reference lakes averaged 46 (33–60) of which 63% were rotifers. Mean cumulative species richness and mean diversity in logged and burnt lakes did not differ from those in reference lakes.3. Lake species assemblages were described by the density of 62 species (41 rotifers and 21 crustaceans). Among‐group differences in species assemblages were not significant. Eighteen per cent of the total variability in species assemblages could be explained by 13 environmental factors, among which dissolved oxygen concentration and cyanobacteria biovolume were the most important. About 5% of species assemblage variability was attributed to covariation between environmental factors and time of sampling, while 4.1% was attributed to temporal variation.4. Variations in zooplankton species richness and assemblages in Boreal Shield lakes are important, both among lakes and among sampling dates. They seem to depend on environmental factors unrelated to catchment‐based perturbations, at least on the short‐term of 1 year.

Ecology of four turbid clay pans during a filling-drying cycle in the Paroo, semi-arid Australia

The clay pans studied were small (<2 ha), shallow (<30 cm) and contained very turbid, alkaline water of low conductivity for 40–90 days. Nutrients peaked early but chlorophyll-a values varied through time. Water temperatures ranged from 3.5 to 25.5 °C. Cumulative species richness ranged from 30 to 55, with mean momentary species richness varying from 15.5 to 29.1 among the four pans. Macroinvertebrate assemblages were dominated by adult phyllopods, hemipterans and coleopterans, and zooplankton was dominated by juvenile phyllopods, copepods and cladocerans. No macrophytes were present. Ordination showed two pairs of pans (A+B and C+D) which matched ordination of physicochemical data, with turbidity the factor best explaining the pattern. Macroinvertebrate assemblages varied between the centre and littoral zone of all pans, particularly in C and D in which CPOM was more abundant in the littoral. Grouping of assemblages was directed as much by differences in abundance as variation in species composition. Succession was directional and continuous. Among macroinvertebrates, insects dominated initially and terminally, but phyllopod crustaceans were important much of the time. In the zooplankton, phyllopods dominated initially then entomostracans, with final assemblages mostly consisting of copepods. Succession was quicker and later assemblages more stable in zooplankton. The feeding group of filter feeders/collectors dominated during the life of the pans, except at the beginning and end when predators were important. The major carbon source was algal, despite the high turbidity and abundant detrital matter.

Influence of host ecology and morphology on the diversity of Neotropical bird lice

Host‐parasite systems can be powerful arenas in which to explore factors influencing community structure. We used a comparative approach to examine the influence of host ecology and morphology on the diversity of chewing lice (Insecta: Phthiraptera) among 52 species of Peruvian birds. For each host species we calculated two components of parasite diversity: 1) cumulative species richness, and 2) mean abundance. We tested for correlations between these parasite indices and 13 host ecological and morphological variables. Host ecological variables included geographic range size, local population density, and microhabitat use. Host morphological variables included body mass, plumage depth, and standard dimensions of bill, foot and toenail morphology, all of which could influence the efficiency of anti‐parasite grooming. Data were analysed using statistical and comparative methods that control for sampling effort and host phylogeny. None of the independent host variables correlated with louse species richness when treated as a dependent variable. When richness was treated as an independent variable, however, it was positively correlated with mean louse abundance. Host body mass was also positively correlated with mean louse abundance. When louse richness and host body mass were held constant, mean louse abundance correlated negatively with the degree to which the upper mandible of the host's bill overhangs the lower mandible. This correlation suggests that birds with longer overhangs are better at controlling lice during preening. We propose a specific functional hypothesis in which preening damages lice by exerting a shearing force between the overhang and the tip of the lower mandible. This study is the first to suggest a parasite‐control function of such a detailed component of bill morphology across species. Avian biologists have traditionally focused almost exclusively on bills as tools for feeding. We suggest that the adaptive radiation of bill morphology should be reinterpreted with both preening and feeding in mind.

Small-scale dynamics of desert annuals in an ungrazed Rhanterium epapposum community over three growth seasons in Kuwait

Summary Two blocks, each consisting of twelve 0.25 m2 permanent plots (0.5 × 0.5 m), were established in a community dominated by desert annuals in an area of Kuwait protected from grazing. Small-scale dynamics of desert annuals, cumulative species richness and inter-annual plot similarity were investigated in plots of both blocks in three growth seasons, 1997, 1998 and 2000. The three study periods had different precipitation patterns in respect of the amount of rainfall received during the growth period, as well as the timing and amount of the first rains to trigger germination. In all three seasons, most species of the cumulative species pool (i.e. all species registered in each block during the study period) were rare, and of the more frequent ones, species turnover was generally high. High turnover is also reflected in a low inter-annual plot similarity. Stochastic climatic factors appear to play a major role in determining species composition and thus species turnover in a particular growth season. Species turnover, mediated by temporal niche partitioning, is generally regarded as an important factor in promoting coexistence in communities dominated by annuals in spatially uniform habitats. However, very high species richness in the particularly favourable growth season 1998, in which over 75% of species of the cumulative species pool were recorded, suggests that in this desert ecosystem characterised by generally very low vegetation cover, the role of species turnover in maintaining diversity may not be as important as in other ecosystems dominated by annuals.

Fish fauna associated with floating objects sampled by experimental and commercial purse nets

SUMMARY: Based on the commercial surrounding nets traditionally used in the Coryphaena hippurus fishery, we designed an experimental purse seine (64 m long and 14 m high, with a purse line and a central codend of 2 mm mesh) for sampling fish fauna associated with flotsam. Taxa, number, biomass and sizes of fishes caught with both types of gear around fish aggregation devices were compared. From 63 hauls with the experimental net, we caught 11370 fishes belonging to 17 families and 26 species. In contrast, 816 fishes belonging to 7 species and 5 families were collected from 39 commercial hauls. Despite differences in number of hauls for each net, the curves of cumulative species richness showed that additional hauls could not increase the number of species collected with the commercial net. The most abundant species from experimental net catches were Trachurus picturatus, which represented over 80% of the specimens caught in spring and summer, Naucrates ductor, which represented about 50% of autumn catches, both in terms of abundance and biomass, and Seriola dumerili, which represented 46% and 21% of the samples taken in summer and autumn respectively. Seriola dumeril was also frequent in commercial net catches, in which T. picturatus did not appear, while Coryphaena hippurus and N. ductor represented more than 85% of both abundance and biomass. Large differences between the two types of net were also obtained in the mean fish weight and length frequency distributions of the catches by season. Fish caught with the experimental net ranged from 6 to 570 mm length, while fish collected from commercial hauls had a size range of 35 to 700 mm. The effectiveness of the experimental net in catching small fishes showed that it can be an optimal sampling method not only in the study of fish fauna associated with flotsam, but also in studies to catch early life stages.

Effects of leaf litter species on macroinvertebrate community properties and mosquito yield in Neotropical tree hole microcosms.

Detritus quality and quantity affect macroinvertebrate productivity and distribution in many freshwater ecosystems. This study experimentally investigated the effects of leaf litter from Ceiba pentandra, Dipteryx panamensis, Ficus yoponensis, and Platypodium elegans on macroinvertebrate species composition, richness, and abundance in artificial water-filled tree holes in a lowland moist forest of Panama. Species composition was similar among treatments, but species richness and longevity differed among litter types and were consistently highest with Platypodium litter. Similar patterns were observed in natural tree holes of the focal tree species. The mosquito Culex mollis was the most abundant species in the field experiment. Average conductivity and dissolved oxygen concentration differed among leaf species, but pH did not. Leaf toughness was positively correlated with mean macroinvertebrate abundance and cumulative species richness. A laboratory experiment measured C. mollis yield and pupation time in tree hole microcosms containing the four litter species. Cumulative mosquito mass and time to pupation differed among leaf litter species, with Platypodium litter supporting the greatest yield. Pupation was slowest on Ceiba litter. Grazing by mosquito larvae facilitated leaf decomposition in all treatments. Results suggest that differences in macroinvertebrate species richness and mosquito yield can be attributed to differences in nutritional quality among litter species.

Small‐scale plant dynamics in temperate Themeda triandra grasslands of southeastern Australia

Abstract. Vegetation subjected to two long‐term burning regimes (annual or biennial burning) was studied in permanent plots, at two spatial scales: 0.01 m2 and 1 m2, to determine the small‐scale dynamics of plants in temperate Themeda triandra grasslands of southeastern Australia. Species turnover rates were estimated by presence/absence data while species mobility was assessed using cumulative frequency data.While mean species richness did not fluctuate greatly between years, the vegetation was internally dynamic rather than static. Cumulative species richness increased by 50% at both spatial scales and sites over the 4‐yr study period. However, few species became cumulatively frequent (i.e. occurred in 80% of plots in the first and/or subsequent years), suggesting that cumulative species richness increases were due to small‐ or local‐scale movements of plants, rather than ‘shifting clouds’ of species moving across the entire site. The vegetation's dynamics did not differ greatly at sites subject to different (frequent) fire intervals.Species turnover and mobility were individualistic, but the dynamics of many species was greater at the smaller spatial scale: 31–48% of the species present at both spatial scales at the two sites had higher turnover rates at the 0.01 m2 scale. Similarly, some ‘non‐mobile’ species at the 1‐m2 scale (i.e. ‘constant’ or ‘local’ mobility types), were more mobile at the smaller‐scale. Turnover rate and mobility type were strongly associated with life form in some cases, particularly at the annually‐burnt site. In general, therophytes (and to a lesser degree, geophytes) were positively associated with high turnover and mobility in most years, while hemicryptophytes were negatively associated with high turnover in many instances. Hemicryptophytes included many species with a range of mobility types and hence, few significant associations between mobility and this life form were found.The previously unrecognized internal dynamics of this community under ‘stable’ management regimes contributes to species coexistence by allowing plants with different dynamics properties to persist in a spatially and temporally unpredictable manner. Frequent burning is presumably the important component driving much of the non‐directional, small‐scale dynamics because it regularly destroys individual plants and aerial plant parts and creates opportunities for seedling regeneration, whilst permitting the vegetative persistence and spread of established plants in non‐light‐limited microsites.

Corridors maintain species richness in the fragmented landscapes of a microecosystem

Theory predicts that species richness or single-species populations can be maintained, or at least extinctions minimized, by boosting rates of immigration. One possible way of achieving this is by establishing corridors of suitable habitat between reserves. Using moss patches as model microecosystems, we provide here probably the first field experimental test of the idea that corridors can reduce the rate of loss of species, and therefore help to maintain species richness. Connecting patches of habitat with corridors did indeed slow the rate of extinction of species, preserving species richness for longer periods of time than in disconnected habitat patches. The pattern of γ-diversity, the cumulative species richness of entire connected systems, is similarly higher than that of fragmented systems, despite the homogenizing effects of movement. Predators are predicted to be more susceptible to fragmentation because of their greater mobility and smaller population sizes. Our data are consistent with this prediction: the proportion of predator species declined significantly in disconnected as compared with connected treatments.

Fitting species–accumulation functions and assessing regional land use impacts on avian diversity

As one samples species from a particular assemblage, the initial rapid rate with which new species are encountered declines with increasing effort. Nine candidate models to characterize species–accumulation functions were compared in a search for a model that consistently fit geographically extensive avian survey data from a wide range of environmental conditions. Landscape‐specific species–accumulation curves generated under a bootstrap resampling plan were best described by a generalized Weibull cumulative distribution function. Traditional species–area models of cumulative species richness as a function of accumulated sample had notable functional bias. The Weibull model fitted species–accumulation data equally well among sixty‐six forested landscapes in the eastern U.S. Landscapes with a greater proportion of agricultural and urban land uses accumulated species more slowly than landscapes which retained a greater proportion of natural habitats (r=−0.64, P&lt;0.001). This finding supports predictions of ecosystem behavior under human land use. There was no evidence that intermediate levels of land use intensity maximized accumulation rates. The approach reviewed in this paper makes no assumptions about the form of the species–abundance distribution or how species are distributed in space, thereby offering some advantages over more conventional diversity indices for characterizing how species assemblages respond to anthropogenic disturbance. Investigation of how species accumulation varies over time in a given geographic area is needed to evaluate fully the potential application of this approach to regional land use planning.

Species Richness of Stream Stones: An Investigation of the Mechanisms Generating the Species-Area Relationship

In an upland fourth-order stream, the fauna dwelling on both natural and artificial stones was found to be highly correlated with stone surface area. The power function model provided a good description of the species-area relationship of the stones. For both types of stones, passive sampling was rejected as an explanation for the species-area relationship. The compilation of cumulative species richness, proceeding in order from the smallest area to the largest area and vice versa revealed a negative fragmentation effect. Groups of small stones harboured an impoverished fauna compared with large stones of the same surface area. Small stones did not harbour a distinctive fauna, but simply a sub-set of the species found on larger stones