ABSTRACT
Describing the spatial distribution of communities is crucial to understanding how environmental disturbance can affect biodiversity. Agricultural lands are susceptible to disturbances of anthropogenic origin and have been identified as ecosystems of conservation concern. Such lands are vulnerable to invasions by anthropogenically introduced non-native plants disturbing habitats. This research focused on the invasion-induced taxonomic filtering of birds with shared habitat requirements. The birds were surveyed along a gradient of invasion-altered areas (far from the invasion, uninvaded although susceptible to invaders, and invaded) to identify changes in bird assemblages (ground/herb dwellers, bush foragers, ecotone birds, and tree foragers) caused by this disturbance. Data were collected from 112 sites sampled in southeastern Poland. There were significantly fewer bird species from each assemblage on invaded sites than on uninvaded sites, although exposed to invasion, despite the decrease in the abundance of only ground/herb dwellers. Beta diversity analysis showed that sites with invasion contained bird communities significantly different from those at other sites. Invasion-induced changes resulted in a significant reduction in the diversity of ground/herb dwellers in comparison with uninvaded sites and created a distinctive bush bird assemblage. This was most likely due to the transformation of the grassland layer and the thickening of the shrub layer by plant invaders, which resemble shrubs in morphology. The results indicated the filtering effect of invasion on bird species composition at the level of two habitat assemblages despite the decreases in bird abundance and species diversity of the whole community.
ABSTRACT
The trade-off between animal's parental reproductive effort and survival is still poorly understood. Parental allocation between the workload during breeding attempts and the parents' own body conditions can be assessed through the offspring quality. Here, I questioned whether the immune responsiveness of female great tits may be considered as a mediator of this trade-off. Specifically, I tested whether (1) the parental reproductive effort decreases, (2) the food composition provided to chicks changes, and (3) whether the nestling immunocompetence and body mass decrease after experimental immunisation. Two populations of great tit Parus major occupying nest boxes were studied in Niepolomice Forest and Krzyszkowice Forest (Southern Poland) in 2011 and 2012, respectively. Three days after hatching, half of the females were challenged with sheep red blood cells (SRBC), while other females were injected with phosphate-buffered saline PBS (control). Six days later, food provided by the parents was collected from nestlings. After another 2 days, the offspring's body mass was measured and wing web swelling in response to an additional phytohaemagglutinin (PHA) injection. In both years, immunocompetence and in 2012 also body mass in the offspring of SRBC-immunised mothers were lower than in control nestlings, indicating a cost of mounting the immune response in the female. Six days after the start of the female treatment, the number of caterpillars and the volume of food items provided by parents to chicks were higher, whereas the number of spiders was lower in nests with SRBC treatment than in control ones. This might be explained by compensational parental feeding after recovery from the inflammation of a female. Thus, the trade-off between parental effort and survival of parents is mediated by the costs incurred for their immunity and can be assessed by the amount and quality of food provided to the nestlings and the offspring condition.
