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Every species has certain habitat requirements, which may be altered by interactions with other co-occurring species. These interactions are mostly ignored in predictive models trying to identify key habitat variables correlated with species population abundance/occurrence. We investigated how the structure of the urban landscape, food resources, potential competitors, predators, and interaction between these factors influence the abundance of house sparrow Passer domesticus and the tree sparrow P. montanus in sixty 25 ha plots distributed randomly across residential areas of the city of Poznań (Poland). The abundance of the house sparrow was positively correlated with the abundance of pigeons but negatively correlated with human-related food resources. There were significant interaction terms between abundances of other urban species and habitat variables in statistical models. For example, the abundance of house sparrow was negatively correlated with the abundance of corvids and tree sparrows but only when food resources were low. The abundance of tree sparrows positively correlated with density of streets and the distance from the city center. The abundance of this species positively correlated with the abundance of corvids when food resources were low but negatively correlated at low covers of green area. Our study indicates that associations between food resources, habitat covers, and the relative abundance of two sparrow species are altered by the abundance of other urban species. Competition, niche separation and social facilitation may be responsible for these interactive effects. Thus, biotic interactions should be included not only as an additive effect but also as an interaction term between abundance and habitat variables in statistical models predicting species abundance and occurrence.

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European souslik (Spermophilus citellus) is an endangered species being the subject of reintroduction plan in some European countries, including Poland. It is important to obtain data about behavior of reintroduced species, especially a reaction to captivity of specimens prepared to release. The aim of this study was to evaluate influence of human exposure on sousliks behavior. Observed animals were kept in Poznań zoo in three enclosures. Two of them (called "high noise") were in part of the zoo available to the visitors, whereas one ("low noise") was in part closed for them. In "high noise" enclosures sousliks spent more time outside burrows and more specimens were present above ground. They also ate and ran more frequently in "high noise" enclosure, whereas emitted loud voices more often in the "low noise" one. In all enclosures more animals were present above grounds in absence of humans. Time spent by one souslik above ground was positively significantly correlated with the number of sousliks outside burrows. European sousliks observed in this study were used to humans and were less vigilant if they were exposed to permanent humans presence, but they did not become tamed and behave in a way similar to free living animals.

A high rate of human-induced disturbance of tropical ecosystems results in enormous loss of biodiversity due to local extinctions. Yet, mechanisms at the population level that lead to the extinction are still poorly understood. Here we tested the hypothesis that human-induced disturbance results in smaller amount of nesting sites for wood-dwelling arthropods that leads to smaller population size and diminished reproduction, and therefore, may promote local extinctions. We completed censuses in less-disturbed and human-disturbed secondary rain forest plots in Puerto Rico. We measured population size and brood production in wood-nesting ants and examined whether these parameters differ between less-disturbed and more-disturbed habitats. In addition, we measured volume of wood parts of all inhabited and potential nesting sites to assess nest site availability. We found that more human-disturbed forests furnish smaller nest sites, resulting in diminished population size and lowered brood production. Our study shows that human-induced disturbance decreases volume of available nesting sites that leads to decreased population size and lowered reproduction. Thus, in addition to the well-documented loss of species richness in human-disturbed tropical habitats, we demonstrated the direct effect of the disturbance that may promote vulnerability of local populations.Electronic supplementary materialThe online version of this article (10.1007/s13744-018-0624-5) contains supplementary material, which is available to authorized users.