Rates Of Species Accumulation Research Articles

Arthropod diversity of exotic vs. native Robinia species in northern Arizona

Summary1 Arthropods were collected on native locust, Robinia neomexicana A. Gray, and exotic Robinia pseudoacacia L. in northern Arizona over a 2‐year period to determine the number of arthropod species and number of individuals present.2 More arthropod species were found on the native (251) than on the exotic Robinia (174).3 Greater species diversity was likewise found on the native than the exotic. The five most numerous insects collected each year accounted for 81% to 91% of the total number collected on the exotic and native Robinia in 1997 and 1998. Only 12 species occurred on both the native and exotic Robinia in both years.4 These findings are discussed in the context of using exotic trees in plantations and ecological theory regarding rates of arthropod species accumulation on exotic hosts.

Sampling Effort and Estimates of Species Richness Based on Prepositioned Area Electrofisher Samples

Abstract Estimates of species richness based on electrofishing data are commonly used to describe the structure of fish communities. One electrofishing method for sampling riverine fishes that has become popular in the last decade is the prepositioned area electrofisher (PAE). We investigated the relationship between sampling effort and fish species richness at seven sites in the Tallapoosa River system, Alabama, based on 1,400 PAE samples collected during 1994 and 1995. First, we estimated species richness at each site using the first-order jackknife and compared observed values and jackknife estimates of species richness to estimates based on historical collection data. Second, we used a permutation procedure and nonlinear regression to examine rates of species accumulation. Third, we used regression to predict the number of PAE samples required to collect the jackknife estimate of species richness at each site during 1994 and 1995. We found that jackknife estimates of species richness generally were le...

The effects of disturbance on forest butterflies using two methods of sampling in Trinidad

The butterfly assemblages of pairs of forest habitats, differing in disturbance level, within the Victoria Mayaro reserve of South-East Trinidad, are described using walk-and-count transects and canopy and understorey fruit traps. The concurrent use of these two butterfly censusing techniques, revealed major but conflicting differences in species accumulation rates under different disturbance conditions. The disturbed evergreen habitat had the significantly highest accumulation rate from walk-and-count data but the significantly lowest from fruit trap data. This reflects the specificity of much of the fruit-feeding guild for closed canopy forest. Disturbed habitats were found to lack a distinct canopy fauna. These results are discussed in light of the intermediate disturbance hypothesis. Within a region of forest, butterflies were found to be more characteristic of a disturbance level than of a particular forest type, lending weight to the belief that butterfly faunas can be used as bioindicators of forest disturbance. Several restricted geographic range species were not adversely affected by forest disturbance, at these levels of disturbance. The butterfly censuses in this study suggest that the optimal strategy for safeguarding butterfly species richness under natural forest management regimes would be to maintain a mosaic of habitats that included areas of undisturbed primary forest and a network of other forest patches, that varied in management regime and level of disturbance.

The effect of overstory composition on understory woody regeneration and species richness in 7-year-old plantations in Costa Rica

Regeneration under tropical plantations has been suggested as a route to facilitate the restoration of natural forests on degraded deforested lands in the tropics. We tested the hypothesis that 7-year-old tree plantations would have greater abundance and species richness of woody colonizers compared to abandoned pastures, but that the response may differ among plantation tree species. Species accumulation curves were constructed for each of seven plantation trees and abandoned pasture. Vochysia guatemalensis and V. ferruginea had higher rates of woody species accumulation in the understory than the other plantations species or the abandoned pasture. When considered by size class of the regeneration, Pentaclethra macroloba plantations had a higher species richness in the 30–200 cm-tall size class compared to the abandoned pastures, and Pinus tecunumanii and Vochysia guatemalensis had greater species richness of stems >200 cm tall compared to the abandoned pasture. Composition of the regeneration was dominated by shrubs, particularly Conostegia subcrustulata. Nevertheless, the Vochysia spp. seemed to favor the presence of a greater diversity of tree species in their understory than the other plantation species. The facilitation of understory development and tree recruitment into the Vochysia plantations may be attributed to suppression of grasses and ferns together with a growth form that attracts seed dispersers. Thus with some plantation species there seems to be a true potential to facilitate a more rapid restoration of a forest community than would occur naturally.

Estimating number of species and relative abundances in stream-fish communities: effects of sampling effort and discontinuous spatial distributions

We sampled fishes and measured microhabitat in series of contiguous habitat units (riffles, runs, pools) in three Virginia streams. We used Monte Carlo simulations to construct hypothetical series of habitat units, then examined how number of species, similarity in relative abundances, and number of microhabitats accumulated with increasing number of habitat units (i.e., sampling effort). Proportions of all species and microhabitats represented were relatively low and variable at low sampling effort, but increased asymptotically and became less variable with greater sampling effort. To facilitate comparisons among streams, we fitted simulation results to negative exponential curves. The curves indicated that 90% of the species present were usually found by sampling 5 to 14 habitat units (stream length of 22–67 stream widths). Estimates of species relative abundances required less sampling effort for a given accuracy than estimates of number of species. Rates of species accumulation (with effort) varied among streams and reflected discontinuity in species distributions among habitat units. Most discontinuity seemed to be due to low population density rather than to habitat selectivity. Results from an Illinois stream corroborated our findings from Virginia, and suggested that greater sampling effort is needed to characterize fish community structure in more homogeneous stream reaches.