Effects of productivity on species–area curves in herbaceous vegetation: evidence from experimental and observational data

Abstract

The effects of productivity on the parameters of the species–area curve were investigated in this paper using two data sets on terrestrial plant communities: (1) one including 48 plots in 12 experimental sites on ploughed, formerly cultivated fields in the Siena region, Italy, and (2) one including 40 plots in hay meadows in the Bremen region, Germany. In both regions, species presence of vascular plants was recorded in nested plots ranging in size from 0.004 to 256 m2 and 0.001 to 1000 m2, respectively. Productivity was estimated as dry standing biomass. In the Siena data set, species richness showed a humped-back relation to biomass in the plot sizes up to 1 m2. For the larger plot sizes, no significant correlations were found. In the Bremen data set, positive relation between species number and biomass was observed at the smallest spatial scale (0.001 m2), whereas the relation disappeared or tended to be negative for the larger plot sizes. In general, the slopes z of the log species–log area curves (SAC) were negatively related to biomass in both data sets, while the intercept c increased with biomass in the Siena data set and was unrelated to biomass in the Bremen data set. The relationship between c and z was negative in the Siena data set and positive in the Bremen data set. The above results differed somewhat depending on which plot sizes were considered for the calculation of the SAC. Literature data confirmed that there are no clear patterns in the inter-correlations between productivity, small scale and large scale species richness. Sites differing in productivity and in the slopes and intercepts of SAC may thus give rise to different species richness–productivity relationships. There can be one possible relation between species richness and biomass at one spatial scale (e.g. humped-back) and another type of relation, even opposite, at another spatial scale. This suggests that the properties of species–area curves do not respond in a uniform way to the changes in productivity, but depend on the type of habitat or plant community and its particular properties. The parameter of the SAC can then hardly be used as scale-independent parameter to investigate the effects of ecological factors, such as productivity, on species richness. The lack of clear patterns in the relations between small scale and large scale species richness implies that the predictions of the species-pool hypothesis may fail when applied to plot sizes as dealt with in this study

Don't Diss Integration: A Comment on Ricklefs's Disintegrating Communities

“…Here, a populous regional species pool of more than 80 species was associated with local species densities of 10 species m Ϫ2 or less; again, local richness was more heavily regulated by competitive exclusion. Given such evidence, it is not surprising that a study conducted in two regions of Europe (Siena, Italy, and Bremen, Germany; Chiarucci et al 2006) found poor correlation between regional species pool size and local species richness.…”

Sand pits as habitats for beetles (Coleoptera): does area affect species number and composition?

“…The SAR was tested using two models: the commonly used log-log power function, S = c A Z (Arrhenius 1921;Tjørve 2003), and a curved model called the quadratic power function, S = 10 (b0?b1 logA?b2 (logA)2) (Chiarucci et al 2006), where S = species number, A = area, z = the slope (z value) and c and b x are constants. The models were chosen to fit our empirical data and according to Dengler (2009) both models generally perform well.…”

“…This is consistent with island biogeography theory (MacArthur and Wilson 1967) and previous SAR studies including beetles (e.g., Lövei et al 2006;Magura et al 2001;Vries de et al 1996). The SAR model that best explained the relationship was the quadratic power function (Chiarucci et al 2006;Dengler 2009), where the fitted SA-curve shows a rapid initial increase in the number of sand species followed by a peak at around 2.5-3 ha and then a decrease (Fig. 3).…”

Species-area relationship within and across functional groups at alpine grasslands on the northern Tibetan Plateau, China

“…Alpine pastures on the Plateau are traditionally grazed by yaks and/or sheep and are managed by single or multiple families (Cao et al 2011;Cao et al 2013). Livestock grazing can affect plant species composition, which influences the form and parameters of SAR in many habitats (Hiernaux 1998;de Bello et al 2007;Chen et al 2008). However, there is lack of available information on the selective grazing behaviors of domestic yaks and sheep on the Northern Tibetan Plateau.…”

“…Therefore, the two theories are not necessarily mutually exclusive, and stochastic processes, environmental filters (temperature, precipitation, moisture and nutrients in soils), and biotic interactions may simultaneously govern local species richness and composition (Lortie et al 2004). For example, Chiarucci et al (2006) suggested that the intercepts and slopes of SAR curves were dependent on habitat types and plant community properties. In our results, we found that both the slopes and intercepts of the SAR curves for all species and forbs were significantly higher in alpine meadows than in alpine steppes ( Figure 3 and Table 2).…”