A negative heterogeneity–diversity relationship found in experimental grassland communities

Abstract

Recent meta-analyses and simulation studies have suggested that the relationship between soil resource heterogeneity and plant diversity (heterogeneity-diversity relationship; HDR) may be negative when heterogeneity occurs at small spatial scales. To explore different mechanisms that can explain a negative HDR, we conducted a mesocosm experiment combining a gradient of soil nutrient availability (low, medium, high) and scale of heterogeneity (homogeneous, large-scale heterogeneous, small-scale heterogeneous). The two heterogeneous treatments were created using chessboard combinations of low and high fertility patches, and had the same overall fertility as the homogeneous medium treatment. Soil patches were designed to be relatively larger (156 cm(2)) and smaller (39 cm(2)) than plant root extent. We found plant diversity was significantly lower in the small-scale heterogeneous treatment compared to the homogeneous treatment of the same fertility. Additionally, low fertility patches in the small-scale heterogeneous treatment had lower diversity than patches of the same size in the low fertility treatment. Shoot and root biomass were larger in the small-scale heterogeneous treatment than in the homogeneous treatment of the same fertility. Further, we found that soil resource heterogeneity may reduce diversity indirectly by increasing shoot biomass, thereby enhancing asymmetric competition for light resources. When soil resource heterogeneity occurs at small spatial scales it can lower plant diversity by increasing asymmetric competition belowground, since plants with large root systems can forage among patches and exploit soil resources. Additionally, small-scale soil heterogeneity may lower diversity indirectly, through increasing light competition, when nutrient uptake by competitive species increases shoot biomass production.

Species richness in a model with resource gradient

“…We have shown that there are many zones over which coexistence of species is possible, contrary to the assumption made by Kadmon and Allouche (2007). We have, however, also demonstrated that in special conditions the negative relation between species richness and heterogeneity found by Kadmon and Allouche (2007); Gazol et al (2013) could also occur.…”

“…Only the appearance of regions where the living conditions are extremely difficult or prevent life at all, could lead to a plateau or even decrease of the SR. Our study confirms therefore earlier claims (MacArthur and Wilson 1963;Hortal et al 2009;Lundholm 2009) that the relationship between SR and GR has a positive character. We show also that the non-significant or negative relationship claimed by Gazol et al (2013); Laanisto et al (2013); Kadmon and Allouche (2007) can also take place, but in special circumstances.…”

“…A topic recently much discussed is whether an increase of heterogeneity has always a positive effect on the species richness (Kadmon and Allouche 2007;Hortal et al 2009;Hortal et al 2013;Gazol et al 2013). Kadmon and Allouche (2007) proposed a model merging two well-know approaches-the island biogeography theory (MacArthur and Wilson 1963;He et al 2005) and the niche model (Silvertown 2004).…”

Species Diversity of Carabid Beetles and Ants of Two Reclaimed Tailing Ponds

“…The heterogeneity-diversity relationship has been investigated in a number of studies, including beetles [26] and other insects [27][28]. However, not all trends are positive [29][30], which is hypothesized to be influenced by the differences in resource availability between the investigated communities [31]. A positive correlation between plant cover and number of carabid species is widely recognized [32][33][34].…”

No consistent effect of plant species richness on resistance to simulated climate change for above- or below-ground processes in managed grasslands

“…This is in line with analyses by Socher et al [16, 17], who report differential effects of management for the three exploratories: the diversity-promoting effect of grazing in the Swabian Alp is inverted into a negative effect in Schorfheide-Chorin. This may be due to grazing disturbance being at a small spatial scale, increasing dominance of tall species in fertile grasslands [29]. We cannot resolve whether it is the regional conditions that led to different correlations between species richness and buffering ability (Fig.…”