Trophic niche partitioning between two Rock Nuthatches (Sitta tephronota&Sitta neumayer) in a contact zone in Iran

Abstract

Two sympatric nuthatch species, Sitta tephronota and S. neumayer, provided the exemplar case of character displacement when the term was coined. The two species are quite similar morphologically but have diverged from one another in sympatry, presumably because of competition-driven selection favoring the partitioning of food resources. However, actual diet partitioning has never been shown. Here, we report the dietary composition of the two species by analyzing items recovered from the gastrointestinal tract. We found that S. tephronata fed predominantly on Coleopterans, Hemipterans and Orthopterans with the most important seed plants taken being Amygdalus lycioides, Ficus carica and Fabaceae, whereas, S. neumayer fed mainly on Coleopterans, Hemipterans and Lepidopteran, with A. lycioides, Fabaceae and Tritium aestivum as the most important plants taken. To determine whether the two species partition prey into different sizes, we examined two mostly abundant insect preys (Hemipterans and Coleopterans) and measured head length for Hemipterans and mandible size for Coleopterans as proxies for prey body size. We found a significant relationship between bird body size and prey size, as S. tephronata, which is larger, captured larger bugs and beetles. We also measured the ability of each species to crack seeds of different hardness, finding that S. tephronata takes larger and harder seeds than S. neumayer. Analyses of trophic niche breadth and overlap showed (1) that trophic niche breadth for S. neumayer was wider than that for S. tephronata; (2) overall trophic niche overlap was considerably high but (3) overlap in the size of the most frequently consumed insects was low, suggesting that the species may be partitioning resources by prey size. We conclude that the relative body size of consumed prey is an important axis of niche partitioning and may have driven character displacement in associated trophic traits, allowing the stable coexistence of the two species.

The ecological and evolutionary significance of effectiveness landscapes in mutualistic interactions

“…Although nuthatches (Sittidae) cache seeds, their diets are dominated by insects (e.g. Mohammadi et al, 2016) and they immediately consume many transported seeds (Hutchins et al, 1996). Paca (Cuniculidae) are highly frugivorous generalist herbivores that destroy many seeds (Beck-King et al, 1999) while discarding others intact and apparently seldom caching seeds (Pimentel & Tabarelli, 2004).…”

Micro‐spatial separation and associated morphological adaptations in the original case of avian character displacement

“…Trophic niche segregation for nuthatches through divergence in diet has been established (Grant , Mohammadi et al . ). Apart from confirming this, our study suggests that as well as food type, Western Rock Nuthatch and Eastern Rock Nuthatch also differ in their micro‐habitat preference.…”

Potential prey and conservation implications of the Algerian Nuthatch Sitta ledanti (Vielliard 1976)

“…The same is true for the diet of other nuthatches studied elsewhere in the world, where it is dominated by arthropods. 2,49,3,50,8 Gastropods are also eaten with low proportion by the Eurasian Nuthatch. 51 This difference between the proportions of Arthropods and Molluscs found in the nestlings' fecal sacs could be linked to the most profitable prey choices in terms of energy intake 52,53 ; where the Algerian Nuthatch consumed much less gastropods because of their low nutritional value per unit of time, especially for large snails.…”

“…Most research on the nuthatches' diet has been conducted on adults. [1][2][3] However, studies of nestlings' diet have been largely ignored; even it is believed that nestlings' diet is similar to those of adults. 4 To understand the biology and ecology of birds, studies on nestlings' diet are necessary.…”

“…It's contains arthropods, spiders and plant material. [1][2][3] Nonetheless, we chose to examine the nestlings' fecal sacs for this study since it is more appropriate from the standpoint that it provides the opportunity to not kill or disturb the birds, especially for endemic and threatened species such as the Algerian Nuthatch. 9 However, no detailed description of the Mesogean nuthatches diet' has been provided, with the exception of the Algerian Nuthatch 8 wherethe European earwig (Forficula auricularia) is the main prey to feed its nestlings, and the species searches for arthropods in the dead wood of all types of trees during the breeding season, preferring the Algerian oak (Quercus canariensis) as the main support for food quests.…”