Testing habitat copying in breeding habitat selection in a species adapted to variable environments

The habitat copying hypothesis states that animals use the reproductive performance of conspecifics to evaluate habitat quality and choose their future breeding site. We used data from Audouin's Gull Larus audouinii (1992–2003), a species adapted to unpredictable environments, to analyse subcolony (as patch) choice within a colony (small spatial scale). We also assessed the suitability of alternative hypotheses to the habitat copying hypothesis. The probability of subcolonies being reoccupied annually increased with their size (as number of nests), which suggests the existence of group adherence effects. Subcolony growth rate was related to its average reproductive success (or patch reproductive success) in the previous year: the higher the reproductive success in a colony, the higher the probability of growth the following year. However, this last result was obtained without considering the effect of colony size on the response variable because colony size is related to it. Therefore, results suggest at the population level that in this system habitat copying might either be one of the strategies used by the species in selecting its breeding habitat, or one of the possible strategies operating alone. The other strategies are group adherence mechanisms, and also the effect of conspecific attraction. At the individual level we failed to find evidence of habitat copying and only the previous success of an individual affected its fidelity to a subcolony. The importance of the lack of environmental predictability in the system is discussed, as predictability is a prerequisite of habitat copying.     

Contribution of space remote sensing to river studies

• 1 A review is presented of types of satellite remote-sensing data currently available, and their recent uses in studies of river systems.
• 2 Broad-scale assessments of relative water quality may be carried out, although precise indication of water quality requires samples to be taken in situ.
• 3 In the event of flooding, the extent of inundation may be determined and damage assessed quickly. Some radar data allow measurements of flood water even when obscured by vegetation.
• 4 Riparian vegetation may be mapped over large areas, although the recognition of specific tree species remains difficult.
• 5 One of the most basic and widely used applications of remote-sensing data for rivers is that of mapping, both as a single event and over time to follow changes, e.g. channels in a delta. Entire catchments may be mapped, although the efficiency of detection of low-order streams is dependent upon the characteristics of the system used.
• 6 Remote-sensing data has been widely used in all of the above types of study, but is rarely employed on a long-term basis. Several factors can explain this situation, including, for example, the absence of reliable absolute relationships between spectral data and ecological parameters.
• 7 A clear definition of observational needs (e.g. spectral bands, ground resolution, acquisition frequency) of stream ecologists, together with the identification of ecological parameters that may be collected relatively easily from space, will improve remote sensing as an ecological tool in many restoration and management situations.

     

A study of the diversity and geographical variation in numbers of leg‐bearing segments in centipedes (Chilopoda: Geophilomorpha) in north‐western Europe

Five species of geophilomorphs, Strigamia maritima (Leach, 1817), Geophilus flavus (De Geer, 1778), Geophilus truncorum Bergsøe and Meinert, 1866, Geophilus proximus C. L. Koch, 1847, and Pachymerium ferrugineum (C. L. Koch, 1835), from various sample sites in north‐western Europe were examined for numbers of leg‐bearing segments. Where data was adequate, mean segment numbers were correlated with latitudinal gradients for each species. Solely in S. maritima and some populations of P. ferrugineum did the results show a highly significant geographic pattern towards more leg‐bearing segments in southern populations of both sexes. As concerns G. proximus, we presented for the first time a remarkable geographic shift towards an increased number of pairs of legs in northern populations. Contrary to the conventional geographic pattern, we found that G. flavus and G. truncorum did not exhibit a north–south increase or decrease in segment number. Although there was no general/universal evidence supporting the occurrence of a significant regression slope between mean segment number and latitude/temperature, more information shows that the overall region‐to‐region segment variation was highly significant in both sexes. In S. maritima and P. ferrugineum mean segment number was correlated with the north–south temperature cline. The same was not observed in G. proximus. Parthenogenesis in G. proximus, and a series of ecological characteristics such as habitat preferences, spatial distribution, and fragmented populations could explain the presence or absence of a geographic patterning of segment number variation along a latitudinal cline. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 899–909.     

Population trends in Kittiwake Rissa tridactyla colonies in relation to tick infestation

Parasite and disease transmission has long been considered one of the main costs of group living, but there is still little empirical evidence. Most seabird species breed in dense colonies and occupy the same breeding sites for many years and thus could be exposed to deleterious levels of haematophagous ectoparasite infestations. The aims of this study were to provide information on the epidemiology of the tick Ixodes uriae and to investigate the relationship between Kittiwake Rissa tridactyla colony population trends and local levels of tick infestation in chicks. It is based on a cross-sectional survey of a large sample of British Kittiwake colonies (22 colonies more than 30 years old and situated on natural cliffs). Ixodes uriae was by far the most common ectoparasite detected and was found in all colonies examined. Ticks were aggregated between nests, but not between siblings. Very young and old chicks were far less parasitized than chicks of intermediate age and were excluded from the analysis. Among colonies for which we had good data on population trends in Kittiwakes, those decreasing in number had a higher prevalence and density of ticks than those which were increasing. We suggest that this correlation reveals a cause-and-effect relationship. By influencing the local reproductive success, ectoparasites can affect the recruitment of new breeders and the breeders' site fidelity in the following year, thus influencing the local trend of numbers. This causal link highlights the potential effect of parasites on their host population and thus needs to be investigated further.     

Habitat carrying capacity is reached for the European eel in a small coastal catchment: evidence and implications for managing eel stocks

1. Despite carrying capacity being one of the most important parameters in population management and modelling, we lack substantial evidence for habitat limitations on freshwater species. Here we tested the ideal free distribution (IFD) hypothesis using an indirect behaviour‐based method for small closed populations assuming that animals can effectively estimate habitat suitability and distribute themselves accordingly in time and space. 2. We analysed spatiotemporal variations in the density of the European eel Anguilla, a catadromous species with good colonisation abilities in a small coastal catchment in France. The general linear model used enabled us to test simultaneously the effect of temporal, macro‐ and meso‐scale habitat factors on the presence and abundance of eels at 30 sites over an 8‐year period. 3. Almost every site sampled had eels, whatever its location on the catchment and its habitat characteristics. Density estimates (overall mean ± SD of 0.40 ± 0.48 m^?2) were at the upper range of other values for European catchments. Moreover, eel densities were mainly influenced by the availability of suitable habitats (rocky substratum and instream cover), which suggests that their distribution reflects an IFD. 4. Despite marked variability in recruitment, the density of the oldest size‐class remained stable over the study, suggesting that density‐dependent mortality occurred, probably due to intraspecific competition for space and food and to predation. 5. These findings suggest that eel habitats are saturated in the Frémur. Therefore, we suggest that the mean abundance of eels observed could serve as a threshold value for other male‐dominated river stocks (provided they have a similar overall percentage of suitable habitats) that are common in small, low gradient streams on the north‐Atlantic coast of Europe.     

Low levels of ribosomal RNA partly account for the very high photosynthetic phosphorus‐use efficiency of Proteaceae species

Proteaceae species in south‐western Australia occur on phosphorus‐ (P) impoverished soils. Their leaves contain very low P levels, but have relatively high rates of photosynthesis. We measured ribosomal RNA (rRNA) abundance, soluble protein, activities of several enzymes and glucose 6‐phosphate (Glc6P) levels in expanding and mature leaves of six Proteaceae species in their natural habitat. The results were compared with those for Arabidopsis thaliana. Compared with A. thaliana, immature leaves of Proteaceae species contained very low levels of rRNA, especially plastidic rRNA. Proteaceae species showed slow development of the photosynthetic apparatus (‘delayed greening’), with young leaves having very low levels of chlorophyll and Calvin–Benson cycle enzymes. In mature leaves, soluble protein and Calvin–Benson cycle enzyme activities were low, but Glc6P levels were similar to those in A. thaliana. We propose that low ribosome abundance contributes to the high P efficiency of these Proteaceae species in three ways: (1) less P is invested in ribosomes; (2) the rate of growth and, hence, demand for P is low; and (3) the especially low plastidic ribosome abundance in young leaves delays formation of the photosynthetic machinery, spreading investment of P in rRNA. Although Calvin–Benson cycle enzyme activities are low, Glc6P levels are maintained, allowing their effective use.