Species-area curves and estimates of total species richness in an old-field chronosequence

Average species-area curves were generated for vascular plants in 20 old-fields that were sampled in 1983, 1989, and 1994. These curves were fit with a saturating function to estimate total species richness for each old-field. Additional estimates of total species richness were generated by fitting the same saturating function to subsets of the species area curves and with a first-order jackknife procedure. Estimates of total species richness were strongly correlated with observed species richness. There was limited evidence suggesting that greater sampling was necessary to identify the same proportion of species in older, more species-rich old-fields.     

Short-term waterlogging increases arbuscular mycorrhizal fungal species richness and shifts community composition

Plant and Soil - Our aim was to investigate the effects of short-term waterlogging in shaping communities of the obligately aerobic AMF in roots of Populus deltoides. AMF community in populus roots...     

Benthic insects in Swedish lake-outlet streams: patterns in species richness and assemblage structure

1. We studied how species richness of three hierarchical insect species groups, namely all benthic, lotic and filtering taxa, were related to a number of environmental variables in a data set from fifteen Swedish lake outlets. 2. In partial least-squares analyses, we found that size-related factors (stream width, discharge) and velocity-related factors (current velocity, substratum particle size) were positively associated, and productivity-related factors (chlorophyll a, seston energy, conductivity) negatively associated, with the species richness of the three groups. 3. The weak and negative relationship of richness with productivity largely negated theoretical predictions, whereas the species-environment results corroborated earlier findings from running water systems. 4. The most important factors associated with the species composition of the lake outlets studied included pH, lake area, discharge, channel width and detritus. 5. Of the filter feeders, most species of blackflies (Diptera: Simuliidae) showed a negative relationship with pH. 6. A nested subset analysis demonstrated that species-poor sites did not have a subset of species found at more species-rich sites in any of the three hierarchical groups.     

Implications of shifts in coffee production on tree species richness, composition and structure on small farms around Mount Kenya

Small coffee farms around Mount Kenya in Kenya contain many planted and remnant tree species but little is known in the region about the relationship between trees on farms and the methods and dynamics of coffee production. Shifts in production may alter tree diversity and potentially impact on future biodiversity conservation efforts by affecting niches available for indigenous trees on farms. Here, knowledge was gathered on how changes in coffee production on 180 small farms around Mount Kenya may affect tree diversity, categorizing farms according to coffee yield levels over a period of five years as increasing, decreasing or stable production. Tree species richness, abundance and composition were analyzed using species accumulation curves, Rènyi diversity profiles, rank abundance and ecological distance ordinations, and the effects of coffee production examined using quasi-Poisson generalized linear regressions. Species richness were positively correlated with tree basal area but negatively related to coffee, banana and maize yields value. A difference in average tree species richness, abundance and basal area on increasing farms was observed compared to the decreasing and stable farms, even though formal tests on richness and densities differences were inconclusive. These dynamics do not significantly influence vegetation structure but seem to have a bearing on species composition on farms of different coffee production. The overall low abundance (23 % of trees) but high richness (78 % of species) of indigenous trees on coffee farms could change markedly if the dynamics observed in the current study persist, indicating the need for the development of intensified multi-species cropping systems.     

Effects of rain forest logging on species richness and assemblage composition of small mammals in Southeast Asia

Aim The effects of logging and habitat degradation on the richness and abundance of small mammals in Asian rain forests are largely unknown. This work compares the species richness, dominance and evenness of small non‐volant mammals between logged and unlogged forests, and assesses whether assemblage variability (β‐diversity) is similar between forest types. Location Southeast Asia, northern Borneo (Sabah, Malaysia), Sunda‐shelf. Methods We surveyed species‐rich assemblages of small non‐volant mammals in three unlogged and three logged forests for 2 years. At each forest site, we sampled a permanently marked transect and two additional sites in three trapping sessions. All analyses were performed at both levels to include the effects of local abundances and point estimates, separately from the relative abundances of species on a more regional scale. Results We trapped a total of 1218 individuals of 28 species. Eleven common species accounted for 95% of all captures. Species richness and diversity were significantly higher in unlogged forest (27 species) than in logged forest (17 species). This was mainly attributable to the smaller number of rarely recorded species in logged forest (five compared with 16 in unlogged forest, with a total of fewer than 10 captures). However, all common species were present in both logged and unlogged forests, and our analyses revealed similar patterns of dominance, evenness and fluctuations in abundance. Hence overall assemblage composition in multivariate space did not differ greatly between forest types. Assemblages of Muridae and Tupaiidae showed similar population fluctuations in space and time, indicating that the ecology of these taxa may be partially driven by the same environmental factors. Main conclusions Although species were distributed patchily within sites, analyses at local and regional scales revealed similar patterns in diversity and assemblage variability, suggesting that effects of forest modification did not differ extensively locally and regionally, but had a profound effect on rare species. Our results emphasize the importance and conservation value of logged forest stands that are able to hold a large proportion of the small mammals also found in unlogged forests. Rare and more specialized species are more vulnerable to forest degradation than commonly caught species, resulting in the complete loss, or a decrease in numbers, of certain groups, such as arboreal small mammals and Viverridae.     

Species richness and assemblage structure of Trichoptera in Danish streams

• 1 Species richness and assemblages of Trichoptera from 157 ‘pristine’ Danish lowland stream sites were analyzed, for dependence on geographical position of the sites and simple physical variables, using two way indicator species analysis and detrended correspondence analysis.
• 2 A total of 106 species were recorded, representing ≈ 90% of the species pool known from Danish streams. Only seven species occurred at more than half the sites, whereas an additional 11 species were found at more than a quarter of the sites.
• 3 Although sites showed significant regional differences in environmental variables (stream order, width, slope and presence/absence of riparian forest), species richness and assemblages were primarily correlated with stream order, width and slope. Maximum richness was found at the largest (5th order) stream sites.
• 4 Regional differences in species assemblages were found, with several species being absent from the islands Funen and Bornholm. Species assemblages also differed between forested and non‐forested stream sites.
• 5 We found evidence that stream temperature may be of only minor importance in determining Trichoptera species richness and assemblage composition in Danish streams compared to other size‐related physical factors.

     

Dominant ants can control assemblage species richness in a South African savanna

1. Competition is considered a key factor structuring many communities, and has been described as the 'hallmark' of ant ecology. Dominant species are thought to play a key role structuring local ant assemblages through competitive exclusion. 2. However, while there have been many studies demonstrating competitive exclusion and consequently reduced richness at baits, it is not clear whether such regulation of 'momentary' diversity at clumped food resources can scale up to the regulation of richness at the site or assemblage level. 3. In this study, ant assemblages were sampled in three different savanna habitats in South Africa using both baiting and pitfall trapping. 4. As has been found in previous studies, there was a unimodal relationship between dominant ants and species richness at baits, with high abundances of dominant ants regulating species richness through competitive exclusion. Analysis of pitfall samples revealed strong convergence in pattern, and results from null model co-occurrence analyses supported the findings. 5. The importance of competition in structuring local ant assemblages was, however, only apparent at one of the three savanna habitats suggesting that a full range of extreme environments is needed to produce the full unimodal relationship at the assemblage level. 6. Although the relative importance of competition varied with habitat type, the study demonstrated that in some habitats, dominant ants can control species richness at the assemblage level.     

Rapid inventory of the ant assemblage in a temperate hardwood forest: species composition and assessment of sampling methods

Ants are key indicators of ecological change, but few studies have investigated how ant assemblages respond to dramatic changes in vegetation structure in temperate forests. Pests and pathogens are causing widespread loss of dominant canopy tree species; ant species composition and abundance may be very sensitive to such losses. Before the experimental removal of red oak trees to simulate effects of sudden oak death and examine the long-term impact of oak loss at the Black Rock Forest (Cornwall, NY), we carried out a rapid assessment of the ant assemblage in a 10-ha experimental area. We also determined the efficacy in a northern temperate forest of five different collecting methods--pitfall traps, litter samples, tuna fish and cookie baits, and hand collection--routinely used to sample ants in tropical systems. A total of 33 species in 14 genera were collected and identified; the myrmecines, Aphaenogaster rudis and Myrmica punctiventris, and the formicine Formica neogagates were the most common and abundant species encountered. Ninety-four percent (31 of 33) of the species were collected by litter sampling and structured hand sampling together, and we conclude that, in combination, these two methods are sufficient to assess species richness and composition of ant assemblages in northern temperate forests. Using new, unbiased estimators, we project that 38-58 ant species are likely to occur at Black Rock Forest. Loss of oak from these forests may favor Camponotus species that nest in decomposing wood and open habitat specialists in the genus Lasius.     

Altering the balance between bacterial production and protistan bacterivory triggers shifts in freshwater bacterial community composition

Bacterivorous protists are known to induce changes in bacterial community composition (BCC). We hypothesized that changes in BCC could be related quantitatively to a measure of grazing: the ratio of bacterial mortality to growth rate. To test this hypothesis, we analyzed time-course changes in BCC, protistan grazing rate, and bacterial production from 3 in situ studies conducted in a freshwater reservoir and three laboratory studies. In the field experiments, samples were manipulated to yield different levels of protistan bacterivory and incubated in dialysis bags. Laboratory investigations were continuous cultivation studies in which different bacterivorous protists were added to bacterial communities. BCC was assessed using 4–6 different rRNA-targeted oligonucleotide probes for community analysis. Change in BCC (Δ BCC) was estimated as the sum of changes in the proportions of the two phylogenetic groups that showed the largest shifts. Analysis of a set of 22 estimates of shifts in the ratio of grazing to production rate over periods of 48–72 h and Δ BCC showed that Δ BCC was positively and tightly correlated (r ² = 0.784) with shifts in the ratio of grazing mortality to cell production. While the nature of a shift in BCC is unpredictable, the magnitude of the change can be related to changes in the balance between bacterial production and protistan grazing. This revised version was published online in August 2006 with corrections to the Cover Date.     

Bat assemblage structure in two dry forests of Colombia: Composition, species richness, and relative abundance

We studied the composition, species richness, and relative abundance of bat assemblages in the Colombian dry forests of Chicamocha and Patía. In Chicamocha, 11 bats of the family Phyllostomidae were captured with mist-nets, corresponding to 85–100% of the potential phyllostomids species in the area. Two bats of the family Vespertilionidae were also captured in Chicamocha. In Patía, 12 species were captured with mist-nets, all Phyllostomidae, representing 72–100% of the estimated total number of species in the zone. Minor differences in number of species and composition were detected among sampling periods in Chicamocha. The most common species in this dry forest were Glossophaga longirostris and Sturnira lilium. In Patía, notable differences in the number of species and composition were observed among sampling periods, and the most common species were Artibeus jamaicensis, Carollia perspicillata and Phyllostomus discolor. Arid-zone dwelling bats were absent in Patía and we suggest that this absence may be associated with the isolation of Patía from other northern dry zones of Colombia since Quaternary times. There was also low abundance of bats in Patía, which appears to be related to human disturbance. The most abundant phyllostomid bat species in the two dry forests studied are those that include fruit and/or nectar-pollen from columnar cacti as an important proportion of their diets.     

Stochastic relations between species richness and the variability of species composition

Ecological communities change over time and space, and ecologists have long suggested that biodiversity might influence the rate of change. Here we cast new light on this question by demonstrating statistical covariation between species richness and the variability of species abundances and identities within a community (compositional variability). We provide a new analytical framework for several previously published measures of ecosystem functioning and compositional variability. We derive three related variances, each of which measures compositional variability due solely to stochastic sampling processes. Our analyses show that whether relations between species richness and compositional variability are positive, negative or zero, depends on two factors. Not only does the particular variance used affect the relation, but, more importantly, the underlying determinants of species richness can strongly affect the stochastic relations between species richness and compositional variability. This analysis makes clear for the first time how species richness should correlate with important measures of community variability, even in the absence of systematic processes.     

Effects of micrometazoa on the protistan assemblage of a littoral food web

SUMMARY. 1. Effects of two size-classes of micrometazoa (assemblages of rotifers and of rotifers/cladocerans/copepods) on the abundance and composition of a co-occurring, substrate-associated protistan assemblage were assessed by selectively transferring these groups from a small pond to laboratory microcosms.
2. Addition of micrometazoa to the microcosms resulted in significant changes in the dominance of different protistan groups within 7 days, including a substantial decrease in the abundance of larger omnivorous and bactivorous Protozoa, mostly ciliates, and dominant algal taxa, and an increase in the abundance of heterotrophic microflagellates.
3. Mechanisms whereby micrometazoa reduce the abundance of larger heterotrophic protists may include competition for overlapping resources, but probably involves interference and predation as well. Positive effects of Metazoa on the abundance of heterotrophic microflagellates may result from the elimination of ciliates that prey on and compete with smaller Protozoa.
4. Interactions indicated in this study may alter both quantitative and qualitative aspects of energy flow and mineral cycling in benthic food-webs and be part of a larger trophic cascade involving other Metazoa such as fish.     

Country-based patterns of total species richness,endemicity, and threatened species richness in African rodents and insectivores

Country-based patterns of total species richness, endemicity, and threatened species richness in African rodents and insectivores are studied in this paper. We found several patterns which were similar between insectivores and rodents. Indeed, in both groups we observed: (i) a significantly uneven distribution of species richness across countries and geographic regions with highest species richness peaks being in Middle Africa and lowest peaks in Northern Africa, (ii) species richness increasing with rainfall but being independent on a country’s surface area, (iii) in each country, the insectivore total species richness and endemic species richness increases were positively correlated with rodent total species richness and endemic species richness increases. However, number of endemics peaked in South Africa and D.R. Congo in both groups, but also in Tanzania for Insectivores and in Ethiopia for rodents. In addition, the highest numbers of threatened species occurred in D.R. Congo, Rwanda and Uganda for rodents and in South Africa, Tanzania and Cameroon for insectivores. The conservation implications of these results were discussed.     

Biogeographical determinants for total and endemic species richness in a continental archipelago

We examined the relationship between plant species richness and biogeographical variables (island area, island maximum elevation, distance from nearest inhabited island, distance from nearest mainland) using a data set comprising 201 islands of the Aegean archipelago. We found that endemic species richness was strongly correlated to total species richness. Single-island endemic species richness was most strongly correlated to island maximum elevation, and then to island area, with an apparent small island effect for islands smaller than 47 km². Total species richness was most strongly correlated to island area (with no apparent small island effect), and less strongly correlated to island maximum elevation. Distance from the mainland or other inhabited islands displayed limited predictive value in our data set. The slope of the relationship between species richness and geographical factors (island area, elevation, distance from island/mainland) was steeper for endemic species richness than for total richness. Finally, the different scales of endemicity (single-island endemics, island group endemics and Aegean regional endemics) displayed similar qualitative trends and only differed quantitatively. Thus, we conclude that different biogeographical factors act as drivers for total species richness than for endemic species richness.     

Tree species richness and density affect parasitoid diversity in cacao agroforestry

In Brazil, cacao is mostly planted beneath shade trees. The diversity of shade trees varies from monospecific to highly diverse canopies, characteristic of pristine Atlantic Forest. This study evaluates the relationships between family richness of Hymenoptera-Parasitica and Chrysidoidea, and tree species richness and density, the species richness of herbaceous understorey, and the area and age of the cacao agroforestry system. We sampled 16 cacao agroforestry systems, with canopy diversity ranging from one to 22 tree species per hectare, in three seasons: summer (March), winter (August) and spring (November). Parasitoids were sampled using eight Malaise-Townes traps per site. Tree species richness and density were enumerated within 1 ha at each site, and herbaceous plant species richness was calculated in eight 1 m² plots, within the hectare. The number of parasitoid families increased with tree species richness and density in spring and summer, but decreased in winter. Neither species richness of herbaceous plants nor area and age of the system affected parasitoid family richness. We suggest that the increase of parasitoid diversity with tree species richness and density in warmer seasons reflects increasing heterogeneity and availability of resources. The decrease in parasitoid family number with tree density in winter may be due to local impoverishment of resources, leading to parasitoid emigration to neighbouring forest remnants. This result implies that a higher diversity of shade trees will help to maintain high parasitoid levels and, in consequence, higher levels of natural enemies of cacao pests, particularly in the warmer seasons. This prediction is borne out in the experience of cacao producers. The proper management of shade tree diversity will play a vital role in maintaining the sustainability of cacao agroforestry production systems in the tropics and, concurrently, will maintain high biodiversity values in these locations.     

Regional patterns of diversity and estimates of global insect species richness

The total number of insect species in the world is an important if elusive figure. We use a fresh approach to estimate global insect species richness, based on biogeographic patterns of diversity of well or better documented taxa. Estimates generated by various calculations, all variations on a theme, largely serve to substantiate suggestions that insect species are likely to number around 10 million or less.     

Copepod feeding in the ocean: scaling patterns,composition of their diet and the bias of estimates due to microzooplankton grazing during incubations

Here, we report insights from the compilation and analysis of data on marine calanoid copepod feeding rates in the ocean. Our study shows that food availability and body weight are major factors shaping copepod feeding rates in the field, with a relatively minor role of temperature. Although the maximal feeding rates of copepods that are observed in the field agree with the well-known 3/4 of body size scaling rule for animals, copepod feeding in the oceans is typically limited and departs from this rule. Ciliates and dinoflagellates appear to be highly relevant in the composition of copepod diets, and this represents an indirect increase in the flux of primary production that is likely to reach the upper trophic levels; this contribution is higher in the less productive systems and may help to explain accounts of proportionally higher standing stocks of copepods supported per unit of primary producer biomass in oligotrophic environments. Contrary to common belief, diatoms emerge from our dataset as small contributors to the diet of copepods, except in some very productive ecosystems. We have also evaluated the bias in the estimation of copepod grazing rates due to within-bottle trophic cascade effects caused by the removal of microheterotrophs by copepods. This release of microzooplankton grazing pressure accounts for a relevant, but moderate, increase in copepod grazing estimates (ca. 20–30%); this bias has an effect on both the carbon flux budgets through copepods and on our view of their diet composition. However, caution is recommended against the indiscriminate use of corrections because they may turn out to be overestimates of the bias. We advise that both uncorrected and corrected grazing rates should be provided in future studies, as they probably correspond to the lower and upper boundaries of the true grazing rates.