Mikael von Numers

Variation in clutch size in relation to nest size in birds

Nests are structures built to support and protect eggs and/or offspring from predators, parasites, and adverse weather conditions. Nests are mainly constructed prior to egg laying, meaning that parent birds must make decisions about nest site choice and nest building behavior before the start of egg-laying. Parent birds should be selected to choose nest sites and to build optimally sized nests, yet our current understanding of clutch size-nest size relationships is limited to small-scale studies performed over short time periods. Here, we quantified the relationship between clutch size and nest size, using an exhaustive database of 116 slope estimates based on 17,472 nests of 21 species of hole and non-hole-nesting birds. There was a significant, positive relationship between clutch size and the base area of the nest box or the nest, and this relationship did not differ significantly between open nesting and hole-nesting species. The slope of the relationship showed significant intraspecific and interspecific heterogeneity among four species of secondary hole-nesting species, but also among all 116 slope estimates. The estimated relationship between clutch size and nest box base area in study sites with more than a single size of nest box was not significantly different from the relationship using studies with only a single size of nest box. The slope of the relationship between clutch size and nest base area in different species of birds was significantly negatively related to minimum base area, and less so to maximum base area in a given study. These findings are consistent with the hypothesis that bird species have a general reaction norm reflecting the relationship between nest size and clutch size. Further, they suggest that scientists may influence the clutch size decisions of hole-nesting birds through the provisioning of nest boxes of varying sizes.

Clutch-size variation in Western Palaearctic secondary hole-nesting passerine birds in relation to nest box design

Secondary hole-nesting birds that do not construct nest holes themselves and hence regularly breed in nest boxes constitute important model systems for field studies in many biological disciplines with hundreds of scientists and amateurs involved. Those research groups are spread over wide geographic areas that experience considerable variation in environmental conditions, and researchers provide nest boxes of varying designs that may inadvertently introduce spatial and temporal variation in reproductive parameters. We quantified the relationship between mean clutch size and nest box size and material after controlling for a range of environmental variables in four of the most widely used model species in the Western Palaearctic: great tit Parus major, blue tit Cyanistes caeruleus, pied flycatcher Ficedula hypoleuca and collared flycatcher F.albicollis from 365 populations and 79610 clutches. Nest floor area and nest box material varied non-randomly across latitudes and longitudes, showing that scientists did not adopt a random box design. Clutch size increased with nest floor area in great tits, but not in blue tits and flycatchers. Clutch size of blue tits was larger in wooden than in concrete nest boxes. These findings demonstrate that the size of nest boxes and material used to construct nest boxes can differentially affect clutch size in different species. The findings also suggest that the nest box design may affect not only focal species, but also indirectly other species through the effects of nest box design on productivity and therefore potentially population density and hence interspecific competition.

High resolution species distribution models of two nesting water bird species: a study of transferability and predictive performance

Species distribution modelling is increasingly used in ecological studies and is particularly useful in conservation planning. Models are, however, typically created with a coarse resolution, although conservation planning often requires a high resolution. In this study we created high resolution models and explored central aspects of the modelling procedure; transferability and predictive performance of the models. We created models for two breeding water bird species, common eider Somateria mollissima and herring gull Larus argentatus, based on data from two regions in the Finnish archipelago (234 islands). We used seven variables which we considered as potential predictors of nest site location: distance to forest, distance to rock and distance to low vegetation, exposure, elevation, slope and curvature of the land surface. We tested the predictive ability of the models crosswise between the areas by using area under the receiver operating characteristic curve. The models were transferable between our study areas and the predictive performance varied from fair to excellent. The most important predictors overall were exposure and distance to forest. More general models, with higher regularization values in the Maxent software, had better transferability regarding predictive performance. However, when we fitted a model based on 60% of the data from both regions and evaluated the model on the remaining 40%, the most complex model had the highest accuracy. Extrapolation of SDMs, evaluated on data from the same region, should therefore always be done with caution as the most accurate model might not have the best transferability if it is not general enough.

Long-Term Changes in Distribution and Frequency of Aquatic Vascular Plants and Charophytes in an Estuary in the Baltic Sea

The long-term impact of natural and human-induced large-scale changes on aquatic phanerogams and charophytes has remained mostly unstudied in the Baltic Sea, largely because of a lack of historical data. A vegetation data set based on transects in an estuary in the western part of the Gulf of Finland studied in the 1930s–1940s, however, exists. We re-surveyed 91 of these transects in 2005 and 2007. The historical data set included 60 species and the contemporary 52 species. The species were classified into increasing, decreasing or unchanged according to the change in their occurrence frequencies. A significant frequency change was found for 31 of the 50 (62%) species which were present in both surveys. The proportion of species/growth forms with high-nitrogen and low-light preferences increased, whereas that of species/growth forms preferring oligotrophic conditions and species of shallow waters decreased. In the area, the species expanded their distribution ranges mainly towards the open sea. Eutrophication, reduced grazing pressure and shore overgrowth by Phragmites australis are suggested as the main reasons for the observed changes. In addition, increased boating and shore-construction activities contributed to the long-term floristic changes.

Interspecific variation in the relationship between clutch size, laying date and intensity of urbanization in four species of hole-nesting birds

Abstract The increase in size of human populations in urban and agricultural areas has resulted in considerable habitat conversion globally. Such anthropogenic areas have specific environmental characteristics, which influence the physiology, life history, and population dynamics of plants and animals. For example, the date of bud burst is advanced in urban compared to nearby natural areas. In some birds, breeding success is determined by synchrony between timing of breeding and peak food abundance. Pertinently, caterpillars are an important food source for the nestlings of many bird species, and their abundance is influenced by environmental factors such as temperature and date of bud burst. Higher temperatures and advanced date of bud burst in urban areas could advance peak caterpillar abundance and thus affect breeding phenology of birds. In order to test whether laying date advance and clutch sizes decrease with the intensity of urbanization, we analyzed the timing of breeding and clutch size in relation to intensity of urbanization as a measure of human impact in 199 nest box plots across Europe, North Africa, and the Middle East (i.e., the Western Palearctic) for four species of hole‐nesters: blue tits (Cyanistes caeruleus), great tits (Parus major), collared flycatchers (Ficedula albicollis), and pied flycatchers (Ficedula hypoleuca). Meanwhile, we estimated the intensity of urbanization as the density of buildings surrounding study plots measured on orthophotographs. For the four study species, the intensity of urbanization was not correlated with laying date. Clutch size in blue and great tits does not seem affected by the intensity of urbanization, while in collared and pied flycatchers it decreased with increasing intensity of urbanization. This is the first large‐scale study showing a species‐specific major correlation between intensity of urbanization and the ecology of breeding. The underlying mechanisms for the relationships between life history and urbanization remain to be determined. We propose that effects of food abundance or quality, temperature, noise, pollution, or disturbance by humans may on their own or in combination affect laying date and/or clutch size.

Sea Shore Plants of the SW Archipelago of Finland — Distribution Patterns and Long-Term Changes during the 20th Century

Historical and contemporary records of 81 vascular plant species of shores from 412 islands in the archipelago of SW Finland are compared to visualise changes in distribution patterns over time, and to identify environmental variables that exert influence on the distribution and on the colonisations and extinctions of species. The environmental variables were measured using GIS. A logistic regression analysis was used to find variables that exert influence on the probability of species occurrences. The total number of species occurrences has increased by 22.7%. On the surveyed islands, frequencies of 60 species have increased or remained unchanged, and those of 21 species have decreased. More species have spread towards less maritime than towards more maritime conditions. Syntheses, including distribution maps, are presented for the species. The decrease in grazing pressure and the eutrophication of the Baltic Sea are probable reasons for the observed changes. Some species have changed their distribution patterns in relation to the environment in unpredictable manners. It is thus concluded that it is worthwhile to analyse the species separately in long term studies when possible.

Testing the potential for predictive modeling and mapping and extending its use as a tool for evaluating management scenarios and economic valuation in the Baltic Sea (PREHAB)

We evaluated performance of species distribution models for predictive mapping, and how models can be used to integrate human pressures into ecological and economic assessments. A selection of 77 biological variables (species, groups of species, and measures of biodiversity) across the Baltic Sea were modeled. Differences among methods, areas, predictor, and response variables were evaluated. Several methods successfully predicted abundance and occurrence of vegetation, invertebrates, fish, and functional aspects of biodiversity. Depth and substrate were among the most important predictors. Models incorporating water clarity were used to predict increasing cover of the brown alga bladderwrack Fucus vesiculosus and increasing reproduction area of perch Perca fluviatilis, but decreasing reproduction areas for pikeperch Sander lucioperca following successful implementation of the Baltic Sea Action Plan. Despite variability in estimated non-market benefits among countries, such changes were highly valued by citizens in the three Baltic countries investigated. We conclude that predictive models are powerful and useful tools for science-based management of the Baltic Sea.

Distribution Patterns and Long-Term Changes in Vascular Plants of Non-Littoral Areas in the SW Archipelago of Finland. Part I. Study Concept and Pteridophyta

The historical (mainly from the 1930s) and current records of 482 vascular plant species or genera of non-littoral areas of 464 islands in the archipelago of SW Finland are compared to visualise changes in distribution patterns and to identify environmental variables that affect the distribution of the species. The environmental variables were measured in the GIS. Logistic regression analysis was used to find variables that affect the probability of species occurrences. Results, including distribution maps, are presented for each species. A synthesis of the study is presented in the last part of this article series.

Changes in Distributions of Selected Vascular Plants in a Baltic Archipelago

The aim of the study was to find indications of climate change by studying changes in frequency and distribution patterns of 18 plant species occurring predominantly on islands. I compared climate-related predictors of islands with species extinctions to islands with colonizations. The study was conducted on 436 islands in the archipelago of SW Finland in the northern Baltic Sea. The data were collected between 1996 and 2012 and, the historical data mainly in the 1930s. I measured predictors, including area, exposure and topographical diversity, in a GIS and used binominal logistic regression to determine which predictors exert an influence on the probability of species occurrence. The number of observations of the selected plants increased by 8.4%, but not by as much as all plant species occurring on the studied islands (10.6%). Species with a generally northern distribution in Finland increased more than thermophilic species. An unambiguous effect of climate warming on the selected plants is not evident. One of the proposed reasons for this is the small-scale topography and the mosaic of different microclimates on the islands that buffer the effect of a large-scale climate warming.

Distribution Patterns and Long-Term Changes in Vascular Plants of Non-Littoral Areas in the SW Archipelago of Finland. Part III. Clusiaceae, Violaceae, Cistaceae, Brassicaceae, Salicaceae, Ericaceae, Pyrolaceae, Monotropaceae, Empetraceae, Primulaceae, Tiliaceae, Malvaceae, Thymelaeaceae, Saxifragaceae, Crassulaceae, Grossulariaceae, Parnassiaceae, Droseraceae

Historical (mainly 1930s) and contemporary records of 482 vascular plant species or genera of non-littoral areas of 464 islands in the archipelago of SW Finland are compared, to visualise changes in distribution patterns, and to identify environmental variables that exert an influence on the distribution of the species. The environmental variables were measured in a GIS. Logistic regression analysis was used to find variables that affect the probability of species occurrences. Results, including distribution maps, are presented for each species. The families Clusiaceae, Violaceae, Cistaceae, Brassicaceae, Salicaceae, Ericaceae, Pyrolaceae, Monotropaceae, Empetraceae, Primulaceae, Tiliaceae, Malvaceae, Thymelaeaceae, Saxifragaceae, Crassulaceae, Grossulariaceae, Parnassiaceae, and Droseraceae are presented in this part of the series. A synthesis of the study will be presented in the last part of this article series.