Relationship between species richness and sampling effort

relationship between species richness and sampling effort

With both species accumulation models, the species richness of the palm relation appeared when individuals were used as sampling effort. Box I. Relationship of Ectoparasite Richness to Number of Papers Published on the . A false negative correlation between sampling effort and parasite species . Species density showed a direct relationship both with volume of the sampled stream segment and fish abundance. It seems plausible that larger streams.

Unit ranking may not require sample identifications to the species level because the primary concern is the relative abundances of focal taxa and how they change across space or time Colwell and CoddingtonOliver and Beattie Normally, community characterization is carried out using one or a few sampling techniques and comprehensive species lists are neither necessary nor feasible DisneyLongino and Colwell Community characterization has most often been used by entomologists, ecologists, and conservation biologists.

Recently, analytical advances focused on examining arthropod ecology have converged with a growing emphasis on including arthropods in rapid biodiversity surveys for conservation purposes WilsonCoddington et al. Accordingly, a number of taxon-specific, structured inventory techniques have been introduced that use a variety of sampling methods that combine the "species hunting" techniques of systematists with the more quantitative methods of ecologists Coddington et al.

This approach serves as a practical, short-term alternative to long-term, comprehensive surveys e. By design, this methodology combines the quantitative approach of community characterization with the objectives of strict inventory.

It permits analyses of inventory completeness and an assessment of the costs and benefits of methods when used individually and in combination Longino and ColwellFisher aDelabie et al.

To assess inventory methods, an account of species captured per sampling method as well as per unit area or time is necessary to evaluate effectiveness. Curves can be constructed to measure either species density the number of species per unit area or species richness the number of species per individual; Gotelli and Colwell Species accumulation curves are similar to rarefaction curves Gotelli and Colwellwhich are produced by randomly and repeatedly resampling a pool of individuals or samples and plotting the number of species represented by increasing numbers of individuals.

In fact, rarefaction curves can be viewed as the statistical expectation of a corresponding species accumulation curve when samples are repeatedly reordered Gotelli and Colwell When the actual number of species in an area is unknown as is typically the case for arthropods the shape of a rarefaction curve can be used to estimate how completely an area has been sampled and how efficiently different methods have captured species in that area Colwell and CoddingtonLongino and ColwellFisher a.

A curve that approaches an asymptote after a large sampling effort is representative of a decrease in species accrual-a measure of sampling completeness Colwell and CoddingtonLongino and ColwellGotelli and Colwell Sampling completeness can be further evaluated by comparing curve asymptotes with values determined by species richness estimators or by observed species richness from well-sampled localities.

When used in combination with a structured inventory, rarefaction curves are intended to permit quantitative analyses of species richness for comparison between methods or between sites. Additionally, subsamples can be evaluated within the context of the entire data set to determine the relative efficiency of method combinations and changes in design e. Among arthropods, ants Hymenoptera: Formicidae have been a focal group for development of structured inventory protocols and novel techniques for analyzing data generated from structured inventory.

Ants are an appropriate group for testing the effectiveness of new methods. They are diverse, abundant, and nearly ubiquitous. They influence the biotic and abiotic processes of the ecosystems where they occur. A majority of species nest in fixed positions, largely ensuring that species dwell where they are sampled. Numerous, established sampling techniques are available, representing a range of costs and yields Bestelmeyer et al.

Furthermore, structured inventory techniques and biodiversity data analyses have been established for inventorying and estimating ant species richness in tropical rainforest ecosystems Fisher, ab, Longino and ColwellAgosti et al. Much less is known about the performance of structured inventory methods to capture ants in subtropical and temperate ecosystems.

Similarly, the performance of species richness estimators remains largely untested on data drawn from temperate or subtropical ant communities. The biodiversity crisis is not confined to the tropics Platnick and neither are the goals of conservation biology, entomology, and ecology. Accordingly, improving structured inventory methods and species richness estimation for ants and arthropods in a variety of ecosystems is warranted.

In this study, we evaluated the efficiency of a structured inventory of ants in northern and central Florida. In so doing, we compared the efficiency of four individual sampling methods and the performance of three species richness estimation techniques. The ant fauna of Florida has been thoroughly surveyed in the past 50 yr throughout the state Van Pelt, Deyrup and TragerDeyrup et al.

As a result, there is a clear record of distribution and habitat association for a majority of species Deyrup Consequently, this study presented a unique opportunity to compare inventory results and species richness estimations with approximate species richness values expected at local and regional scales.

In evaluating sampling methods our objectives were 1 to compare the number of ant species captured by baits, pitfalls, litter extraction, and hand-collecting methods and combinations thereof in five different ecosystems, 2 to compare the complementarity of sampling methods, and 3 to determine the relative costs in time of sampling methods. These objectives permit an analysis of the efficiency of sampling methods in the context of facilitating conservation or land-planning decisions that require comparable estimates of species richness and endemism Coddington et al.

relationship between species richness and sampling effort

Materials and Methods Study Area. A detailed description of the ecosystems sampled and the methods used in this study can be found in King Briefly, this study was carried out in 3 sites in each of five different ecosystems a total of 15 study sites in north and central Florida. The plant community descriptions of Myers and Ewel were used as a basis for ecosystem selection. These sites were selected a priori because they contain some of the remaining nearly undisturbed native upland ecosystems in Florida.

We also sampled a non-native ecosystem, consisting of converted previously cleared fields, to represent moderately disturbed habitat. The ecosystems sampled represent a gradient of upland plant communities that include closed-canopy, hardwood forests, open-canopy pine and oak woodland, and completely open, herbaceous savannah.

Ants were sampled from June through September using baits, pitfall traps, leaf litter extraction with Berlese funnels, and hand collecting.

relationship between species richness and sampling effort

A total of 36 pitfall and 36 litter samples were taken separately at 5-m intervals m total in two parallel lines separated by 10 m Fisher, b A transect of 36 baits was placed between the pitfall and litter extraction lines, with each bait corresponding to pitfall and litter extraction samples.

Traps were buried with the open end flush with the surface of the ground and operated for 3 d. The two samples were pooled; larger objects e. Values calculated with Bootstrap and species accumulation curves were similar to each other and lower than those generated by the Jackknife 1 method Table 4. However, species richness and abundance values, attributes typically used to characterize the structure of fish communities, are known to be very sensitive to sampling effort.

As such, the choice of a sample size that permits the generation of reliable estimates of these attributes is a central question in studies of ecological communities Cao et al. If a sample actually represents the community from which it was collected, it is expected that subsequent samples collected under the same conditions will produce similar values of species density and composition.

In the present study, data obtained for the m reaches of the nine stream segments were extremely variable with respect to composition and species density. This suggests that estimates based on samples of this size may not provide a good enough representation of those fish communities.

Community ecology: Diversity, stability, function

We do not believe that the high variability in species density and assemblage composition observed in our study result from inadequate sampling effort, since our sampling protocol was established based on a large series of samples obtained in several locations in Brazilian Amazon unpublished data. The low abundance of fish in m reaches also represents a common feature of central Amazonian streams.

Furthermore, the very low catches observed at the end of each sampling period indicates a near exhaustion of fishes in each stream reach and support the adequacy of our sampling procedure. A possible disturbance effect generated by the collecting team along the stream segment from first to last reach may also be discarded, since there wasn't any obvious tendency in similarity values obtained along each set of five reaches sampled data not shown.

Habitat heterogeneity is known to have a strong effect on the distribution of fish species along streams, both in function of major longitudinal features e. In the present study, the sampling points were chosen without previous knowledge about habitat heterogeneity i.

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In fact, the lowest species richness was observed in the 1st order stream segment at Fazenda Dimona, which was the smallest of all studied segments and also had a remarkably homogeneous substrate formed mostly by coarse litter.

The relation between sampling effort and species richness as shown by species accumulation curves was steeper in larger stream segments, possibly due to species-area relationships and also environmental heterogeneity Harrel et al. A given length of a higher-order stream segment will have a larger flooded area and a larger volume of water than a similar length of a lower-order stream segment.

The observed variations in fish species richness of same-order stream segments in the present study were partially explained by the volume of water in the segment. The 2nd and 3rd order stream segments at Fazenda Dimona are larger and seemingly more structurally complex than similar-order segments in the other two sites, which might explain the higher species richness observed in that stream.

It seems plausible that larger streams contain higher number of microhabitat types, which allow for the presence of more fish species per stream length. Thus, a larger stream length makes it possible to survey a wider variety of habitats and consequently, to collect rare species that occupy uncommon microhabitats, increasing the species richness recorded.

For example, Zuanon et al. So, the eventual absence of such habitat in a given stream reach or segment would result in the absence of a whole subset of the fish assemblage in that stream section, generating low similarity values among reaches or segments. Although part of the variation in observed fish species density can be explained by differences in stream dimensions and habitat diversity, we cannot rule out the possible effects of stream connectivity to different basins.

The streams located in the Cabo Frio and Km 41 sites are connected by higher-order tributaries to the Amazon River, whereas the Fazenda Dimona stream connects through the Cuieiras River to the Negro River.

This low connectivity and possible effects of an ecological barrier may explain part of the low similarity observed between stream segments in the present study, although historical factors can't be ruled out. Although we observed this trend in our study, the best predictor of species richness was stream segment volume. However, the low number of streams surveyed and presence of outliers e. The extrapolation of species accumulation curves generated reliable estimates of fish species richness in sampled streams.

Such supposed reliability is based on the similarity of values obtained with the Bootstrap and Jackknife methods in fact, a little smaller but within the confidence limits of the Jackknife estimates. It is also known that Jackknife estimates are based on the presence of rare species and tend to overestimate richness when the number of samples is small Krebs, ; Santos, According to our findings and adopting a conservative approachthe fish fauna in these stream segments could be confidently characterized if we use the higher values of stream length estimated for each stream order, that is, m for 1st order, m for 2nd order, and m for 3rd order.

Lyons sampled 10 warm-water streams in southern Wisconsin using a towed electrofishing unit and also found that the recommended length of stream to sample for confidently estimating species richness could be an absolute distance specified in meters. Nevertheless, species richness is often related to the number of habitat units sampled, which varies in function of stream size Simonson et al.

relationship between species richness and sampling effort

Sampling relatively long stream reaches makes it more likely that a sample may include a wide variety of microhabitats and thus reduces the possible effects of different distribution patterns among fish species in the samples. However, we should emphasize that the use of a variety of sampling devices and techniques, including gill nets and fike net traps, especially in larger streams, can add consistency to the protocol we propose here.

The application of the proposed sampling protocol in a variety of habitats and at a wider regional scale would provide important information about its validity for Amazonian terra firme forest streams in general.

Such data would generate information about the variation of fish species diversity and provide reference values that could be used in the characterization of the Amazonian ichthyofauna and definition of fine-tuned regional strategies for biological conservation. The authors thank to R. Literature Cited Angermeier, P.

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