The species–accumulation curve and estimation of species richness

Abstract

Summary 1.One of the general characteristics of ecological communities is that the number of species accumulates with increasing area sampled. However, it is important to distinguish between the species-area relationship and species accumulation curves. The species-area relationship is concerned with the number of species in areas of different size irrespective of the identity of the species within the areas, whereas the species accumulation curve is concerned with accumulation rates of new species over the sampled area and depends on species identity. 2. We derive an exact analytical expression for the expectance and variance of the speciesaccumulation curve in all random subsets of samples from a given area. The analytical species accumulation curve may be approximated by a semilog curve. Both the exact accumulation curve and its semilog approximation are independent of the underlying species abundance distributions, but are influenced strongly by the distribution of species among the samples and the spatial relationship of the samples that are randomized. 3. To estimate species richness in larger areas than that sampled we take account of the spatial relationship between samples by dividing the sampled area into subareas. First a species-accumulation curve is obtained for randomized samples of all the single subareas. Then the species-accumulation curve for all combinations of two subareas is calculated and the procedure is repeated for all subareas. From these curves a new total species (T-S) curve is obtained from the terminal point of the subarea plots. The T-S curve can then be extrapolated to estimate the probable total number of species in the area studied. 4. Data from the Norwegian continental shelf show that extrapolation of the traditional species-accumulation curve gave a large underestimate of total species richness for the whole shelf compared with that predicted by the T-S curve. Application of nonparametric methods also gave large underestimates compared with actual data obtained from more extensive sampling than the data analysed here. Although marine soft sediments sampled in Hong Kong were not as variable as those from the Norwegian shelf, nevertheless here the new method also gave higher estimates of total richness than the traditional species-accumulation approaches. 5. Our data show that both the species-accumulation curve and the accompanying T-S curve apply to large heterogeneous areas varying in depth and sediment properties as well as a relatively small homogeneous area with small variation in depth and sediment properties.

Efeitos da distância entre iscas nas estimativas de abundância e riqueza de formigas em uma floresta de terra-firme na Amazônia Central

“…Em táxons megadiversos, como as formigas, conforme mais indivíduos são amostrados, mais espécies são registradas. Isso acontece porque nesses grupos existem muitas espécies raras (Gotelli e Colwell, 2001;Ugland et al, 2003). Apesar da curva do coletor (Figura 3) não apresentar sinais de estabilização, nossos resultados sugerem que para amostrar 80% das espécies, levando em Tabela 2 -Local de coleta, área amostrada, número de iscas empregado e número de espécies coletado disponíveis em trabalhos que usaram iscas atrativas para coletar formigas em ambientes florestados na Amazônia.…”

Spatial Variability of Sponge Assemblages on the Wellington South Coast,New Zealand

“…Species accumulation curves in PRIMER were plotted for each site using UGE from DIVERSE [89,90]. A one-way ANOVA was used to determine if there were any significant differences in sponge abundance and sponge percentage cover between sites.…”

Additive partition of diversity as standard for the selection of protected areas: the natural reserves network of the Siena province (Italy)

“…In generale, la curva di rarefazione esprime il numero atteso di specie in un piccolo gruppo di n individui o n campioni, preso a caso dal numero N totale degli individui o campioni rilevati (Kobayashi 1974); può essere calcolata sulla media di un numero sufficiente di curve di accumulazione (Gotelli & Colwell 2001) o attraverso l'uso di una formula analitica (Ugland et al 2003, Koellner et al 2004, Chiarucci et al 2008b dove E(S n ) è il numero atteso di specie per il sotto campione di dimensione n, S è il numero di specie totale osservato, N è il numero totale di campioni mentre N i è il numero di campioni in cui è presente l'i-esima specie. In questo caso per numero di cam pioni si intende il numero di plot o di riserve naturali analizzate.…”

“…Tale pattern non è comune, poiché ci si attende che la curva calco lata aggregando tutti i plot sia quella a pendenza maggiore. Questo perché l'insieme di tutti i plot do vrebbe essere più eterogeneo rispetto ai dati prove nienti da un gruppo di campioni uniti da rapporti spaziali più stretti (Ugland et al 2003, Chiaruc ci & Bonini 2005, Chiarucci et al 2009). Per queste ra gioni Lucciola Bella risulta una riserva di estrema importanza che raccoglie un elevatissimo numero di specie focali, ospitate nei diversi habitat che la carat terizzano.…”