Analyzing long-term data from biological surveys

Long-term biological surveys that use a constant sampling regime are rare. This is un- fortunate, as understanding complex biological systems often requires long-term studies. A promising source of long-term data could be the biodiversity monitoring schemes that were implemented in many countries some decades ago. However, scientists have criticized biodiversity monitoring programs and other long-term surveys because they often lack well-articulated scientific hypotheses that were formulated prior to data collection. This is probably the main reason why scientists working on functional biology have only rarely used existing data from such monitoring programs, leading to the fact that a huge body of long-term data is still awaiting analysis.
In the first part of this thesis, I aimed to improve methods for analysing long-term survey data. I developed a new method to estimate demographic parameters without the need to individually mark the animals. Using that method, I was able to obtain yearly survival rates of Nightingales (Luscinia megarhynchos) that were very similar to the survival estimates obtained from a traditional mark-recapture model applied to the ringing data from the same nightingale population. Since data for traditional mark-recapture analyses are rarely available for large spatial scales, the developed model could open up new possibilities by making the data of long-term surveys available for research on animal demography. I presented such an application by applying the developed model to data on Yellowhammers (Emberiza citrinella) from the nation-wide common bird census in Switzerland. I found that territories were colonized at the highest rates in the lowlands. This was in contrast to survival, which was relatively low in the lowlands but tended to increase with altitude. These estimates on demographic rates could not be predicted from the altitudinal patterns of Yellowhammer abundance, which shows highest densities at low altitudes. By providing information on demographic rates, our demographic monitoring framework thus considerably broadens the possibilities for biological inference based on data from large-scale bird monitoring programs.
Important benefits from analysing data of long-term surveys are that these data can be used either to generate new hypotheses about the biological system or to test hypotheses that otherwise would have needed a long-running and expensive experiment. In the second part of the thesis, I presented four case studies with such analyses of long-term survey data. I used the survey data on singing activity in male nightingales to formulate hypotheses about the prospecting activity of females. I then tested the predictions in an experimental setup. I found that the timing of female prospecting corresponded to the period of the night when the singing activity of unpaired males was higher than that of paired males. In contrast to females, territory searching males have been shown to prospect territories almost exclusively during the dawn chorus. At dawn, both paired and unpaired males sang at high rates, suggesting that in contrast to nocturnal singing, dawn singing is important to announce territory occupancy to prospecting males. In the nightingale, the sex-specific timing of prospecting thus corresponded to the differential signalling routines of paired and unpaired males, and the temporal patterns in the behaviour of signallers and receivers thus appeared to be mutually adapted.
In two further case studies, I tested the effectiveness of agri-environment schemes (AES) to promote general biodiversity in the agricultural landscape of the canton Aargau, and to reduce homogenization of floristic communities in Swiss grassland. In the first study, I found that in vascular plants and snails, the species richness increased on plots with AES, but not on control plots without AES, whereas in butterflies and birds, no significant differences were found between AES plots and control plots. I concluded that the agri-environment scheme in the canton of Aargau was effective in protecting and promoting biodiversity, but that the effect depended on the group of organisms. However, when I analysed the grassland of entire Switzerland, I found that in the last decade the floristic communities became more and more similar. Thus, I concluded that local-scale changes in land use regimes implemented by agri-environment schemes and other conservation efforts on parts of the grassland area were apparently not yet sufficient to prevent an overall taxonomic homogenization in the Swiss grassland.