Specialization and niche overlap across spatial scales: Revealing ecological factors shaping species richness and coexistence in Australian songbirds

Abstract

Ecological specialization enables the partitioning of resources and thus can facilitate the coexistence of species and promote higher species richness. Specialization and niche partitioning are expected to exert a decisive influence on local spatial scales, while species richness at regional scales should be shaped mostly by historical factors and abiotic conditions. Moreover, specialization is expected to be particularly important in communities that are exceptionally species rich for their environmental conditions. Concurrently, niche overlap in these communities should be minimized to enable species coexistence. We tested these hypotheses by studying specialization–richness relationship and niche overlap in assemblages of 298 species of songbirds (Passeriformes) across Australia. We used local (2–6 ha) to regional (bioregions) spatial scales and detailed data on habitat, diet and foraging behaviour (method, substrate and stratum). We expected the richness–specialization relationship to be particularly strong (a) on local spatial scales and (b) in communities exceptionally species rich for given environmental conditions (approximated by moisture and vegetation complexity). We also expected (c) low niche overlap in assemblages with specialized species. Only the third prediction was partly supported. First, while the specialization and species richness were often positively related, the strength and the direction of the relationship changed between traits and across spatial scales. The strength of the specialization–richness relationship was consistently positive only in foraging stratum, and it increased towards smaller spatial scales only in case of habitat and diet. Simultaneously, species in local communities demonstrated high overlap in habitat and diet. Second, we did not find particularly strong specialization–richness relationships in exceptionally species‐rich communities. Third, we found the expected negative relationship between specialization and overlap in foraging stratum and substrate (in local communities), suggesting that species partition ecological space locally in terms of where they find food. Our expectations were only weakly supported. Specialization on foraging stratum was probably important in facilitating species coexistence. Conversely, although species were often specialized on habitat and diet, high overlap in these traits did not preclude their local coexistence. Overall, specialization and overlap in foraging traits were more important for species coexistence than habitat or diet.

Ecological niche partitioning in a fragmented landscape between two highly specialized avian flush-pursuit foragers in the Andean zone of sympatry

“…The foraging niche width was wider in the Spectacled Whitestart compared to the Slate-throated Whitestart, which is also consistent with differences in vegetation between the species as a relatively more diverse (less uniform) vegetation structure was detected in the territories of the Spectacled Whitestart than the Slate-throated Whitestart. The ecological niche overlap index based on foraging site location characteristics was in the range of values indicating lower/intermediate degree of niche overlap 57 confirming that the two species differ in their ecological niches. All these results combined with the lack of any observed aggression between the two species are consistent with the ecological sorting mechanism 6 .…”

“…Degree of overlap of resource utilization (foraging niches) between the two species was calculated according to Pianka 67 : where overlaps (O's) are symmetrical and p ij and p ik are the proportions of the ith resource (foraging places type) used by the jth and kth species. The index can range from 0 (no overlap) to 1 (full overlap), but in practice for similar avian foraging site distribution data the range of recorded values is approximately from ~ 0.2 to ~ 0.4 for low overlap and from ~ 0.6 to ~ 0.8 for high niche overlap 57 .…”

Trophic resource partitioning drives fine‐scale coexistence in cryptic bat species

“…Our finding that trophic partitioning only occurs at the fine spatial scale is consistent with other studies of bats (Peixoto et al., 2018), ants (Albrecht & Gotelli, 2001), parasitoid insects (Harvey et al., 2014) and bobcats (Lewis et al., 2015), showing that interspecific interactions are more important for shaping community structure at fine rather than broad spatial scales. However, this pattern is not universal (e.g., Harmáčková et al., 2019). In our study system, these fine‐scale mechanisms could contribute to enabling broad‐scale range overlap across the north of the Iberian Peninsula because theoretical studies have shown that fine‐scale coexistence mechanisms can prevent competitive effects from scaling‐up and affecting the broad‐scale distributions of species (Godsoe et al., 2015).…”

The effects of land degradation on plant community assembly: Implications for the restoration of the Tibetan Plateau

“…This suggests that the higher niche similarity may lead to a more clustered phylogenetic structure (Bennett et al, 2013; Mayfield & Levine, 2010). Likewise, the lower niche overlap intensity in the seriously degraded lands shows that niche differences may be necessary to promote species coexistence in resource‐constrained habitats (Godoy et al, 2014; Harmáčková et al, 2019; Kent et al, 2019). Importantly, the species had a lower species:family ratio and clear variation in phenotypic shapes (such as tall grasses and dwarf forbs) in the highly degraded lands.…”

“…We set an index that is higher than 0.5 as the high spatial overlap degree (R. H. Liu et al, 2018). It can thus be used to assess the potential for competition between species in a community (Harmáčková, Remešová, & Remeš, 2019). We also calculated the Shannon–Wiener niche breadth (Bi) (Colwell & Futuyma, 1971) and overlap (O ik ) (Bewick, Chisholm, Akcay, & Godsoe, 2015; Pianka, 1973) using the following equations: …”