Abstract
Understanding how species sort themselves into communities is essential to explain the mechanisms that maintain biodiversity. Important insights into potential mechanisms of coexistence may be obtained from observation of non-random patterns in community assembly. The spatial niche overlap (Pianka index) and co-occurrence (c-score) patterns in carabid species in three types of steppes (desert steppe, typical steppe, and meadow steppe) in China was investigated. Non randomness was tested using null models. Niche overlap values were significantly higher than expected by chance in the desert steppe, where vegetation cover is less abundant and less uniformly distributed, which possibly forces species to concentrate in certain places. In the typical and meadow steppes, results were influenced by the scale of the analysis. At a broad scale, niche separation was found as a result of species segregation among different sectors (habitats) within these steppes, but when the analysis was conducted at a finer scale, species appeared to be no more segregated than expected by chance. The high co-occurrence averages found in the meadow and typical steppes indicate that the distributions of the species found in a site may be negatively affected by the presence of other species, which suggests that some species tend to exclude (or reduce the abundance of) others. The very low c-score average observed in the desert steppe suggests that competition is not involved there. Thus, in more homogeneous landscapes (such as the typical and meadow steppes), competition might play some role in community structure, whereas spatial variation in the abundances of species is more driven by the uneven spatial distribution of vegetation in the landscape where productivity is lower and less uniformly distributed.
Highlights
The niche concept formalized by Hutchinson (1957) is centered on species co-occurrence
The high average C-scores found in the meadow and typical steppe suggests that the presence of a species is directly affected by the presence of other species, and that competition may have some role in defining species assemblages in these ecosystems, whereas the low value observed in the desert suggests, as above, that competition is not involved here
Our analyses based on the use of null models constructed under different sets of assumptions reveal that spatial niche overlap values in carabid communities inhabiting Central Asian steppes reflect both habitat structure and species interactions, and that results are scale dependent
Summary
The niche concept formalized by Hutchinson (1957) is centered on species co-occurrence. While the fundamental niche is a purely theoretical concept because usually species do not use all the n-dimension in their environment, the realized niche is the part of the fundamental niche which is occupied by the species after its interactions with other species (Vandermeer 1972; Soberón and Arroyo-Peña 2017). High niche overlap may lead to conflictual interactions (such as competition and exclusion) for some species (Giménez Gómez et al 2018; Pascual-Rico et al 2020) or only indicate strong interactions in one niche dimension, with coexistence permitted by only weak interactions in others (Koutsidi et al 2020). Low niche overlap generally indicates lower levels of interaction, thereby allowing sustainable co-existence of species (Koutsidi et al 2020; Yang and Hui 2020)
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