Interspecific interactions and co-existence in dabbling ducks: observations and an experiment

We studied the possible role of resource limitation and interspecific competition in assemblages of dabbling ducks on breeding lakes in Finland and Sweden with observational and experimental data. After initial vegetation mapping and yearly censuses of ducks in 1985–1990, we collected observational data in 1991–1994 from 28 lakes with natural populations of mallard Anas platyrhynchos and teal A. crecca. Mallard and teal co-occur over vast areas in the Holarctic and they are the only breeding dabbling ducks on many oligotrophic lakes. Both species are migratory in our study regions, teal arriving later in spring than mallards. Log-linear model analysis of observational presence/absence data revealed a positive, not a negative, association between the species. This association was independent of habitat diversity as well as of lake size. Mallard-teal interaction was also studied in a cross-over introduction experiment in 32 other lakes in two years. Wing-clipped mallards were introduced to breeding lakes before the arrival of teal to induce resource limitation and interspecific competition, hypothesized to reduce lake use by teal. The density of mallard pairs on experimental lakes was 2.9–8.0 times higher than on controls, but there was no negative response by teal to the treatment. This is the first combined observational-experimental demonstration of lack of interspecific competition in waterfowl. Our results indicate that heterospecific attraction may affect species co-existence in dabbling ducks. Received: 28 October 1996 / Accepted: 13 January 1997     

Habitat distribution of the mallard in relation to vegetation structure,food, and population density

The mallard (Anas platyrhynchos Linnaeus) is a generalist feeder, breeding in a wide range of habitats, yet showing considerable between site differences in density. Variations in density and habitat use may result from inter- and intea-specific competition, habitat structure or food.We studied habitat selection of the mallard in four regions of Finland and Sweden. In each region, ten lakes were chosen ranging from oligotrophic to eutrophic. Habitat distribution of the mallard did not differ between regions despite variation in the density of the species and congenerics. Mallard density did not correlate with vegetation structure, but increased with food abundance and the number and density of congenerics although there were regional differences in mallard response.     

Habitat selection rules in breeding mallards (Anas platyrhynchos): a test of two competing hypotheses

Ideal preemption and conspecific attraction are alternative hypotheses of the habitat selection rules used by individuals. According to the former an occupied site is assumed to be preempted and therefore not available for later arriving individuals, whereas according to the latter individuals are assumed to be attracted by conspecifics to occupied sites, rather than avoiding them. We studied these competing hypotheses in breeding mallards (Anas platyrhynchos) by a cross-over experiment in 2 years, introducing birds onto lakes before migratory wild mallards arrived. If mallards use the ideal preemptive rule, breeding density of wild mallards in experimental lakes should be lower and they should be occupied less frequently than control lakes, but if mallards use the conspecific attraction rule the reverse should be true. Our results allowed us to reject the ideal preemptive rule whereas the conspecific attraction rule was to some extent supported. We discuss these findings in relation to population limitation. The results suggest that the local breeding population studied is not limited by spacing behaviour related to habitat selection. Received: 14 July 1997 / Accepted: 17 November 1997     

Early springs and breeding performance in two sympatric duck species with different migration strategies

The capacity of migratory species to adapt to climate change may depend on their migratory and reproductive strategies. For example, reproductive output is likely to be influenced by how well migration and nesting are timed to temporal patterns of food abundance, or by temperature variations during the brood rearing phase. Based on two decades (1988–2009) of waterfowl counts from a boreal catchment in southern Finland we assessed how variation in ice break‐up date affected nesting phenology and breeding success in two sympatric duck species, Mallard Anas platyrhynchos and Eurasian Teal Anas crecca. In Fennoscandia these species have similar breeding habitat requirements but differ in migration distance; Teal migrate roughly seven times as far as do Mallard. Annual ice break‐up date was used as a proxy of spring ‘earliness’ to test the potential effect of climate change on hatching timing and breeding performance. Both species were capable of adapting their nesting phenology, and bred earlier in years when spring was early. However, the interval from ice break‐up to hatching tended to be longer in early springs in both species, so that broods hatched relatively later than in late springs. Ice break‐up date did not appear to influence annual number of broods per pair or annual mean brood size in either species. Our study therefore does not suggest that breeding performance in Teal and Mallard is negatively affected by advancement of ice break‐up at the population level. However, both species showed a within‐season decline in brood size with increasing interval between ice break‐up and hatching. Our study therefore highlights a disparity between individuals in their capacity to adjust to ice break‐up date, late breeders having a lower breeding success than early breeders. We speculate that breeding success of both species may therefore decline should a consistent trend towards earlier springs occur.     

Testing for cubic smoothing splines under dependent data

Summary In most research on smoothing splines the focus has been on estimation, while inference, especially hypothesis testing, has received less attention. By defining design matrices for fixed and random effects and the structure of the covariance matrices of random errors in an appropriate way, the cubic smoothing spline admits a mixed model formulation, which places this nonparametric smoother firmly in a parametric setting. Thus nonlinear curves can be included with random effects and random coefficients. The smoothing parameter is the ratio of the random‐coefficient and error variances and tests for linear regression reduce to tests for zero random‐coefficient variances. We propose an exact F‐test for the situation and investigate its performance in a real pine stem data set and by simulation experiments. Under certain conditions the suggested methods can also be applied when the data are dependent.     

Moose–vehicle collisions occur earlier in warm springs

After autumn, early summer is the most important moose–vehicle collision (MVC) season in Finland. We surveyed temporal distributions and long-term changes in the timing of MVCs using data of daily collisions that occurred throughout a 4-month season (April–July) for the period 1989–2011. By uniting the road districts, we first divided Finland into five study regions and calculated the annual dates by which 50 % of all the MVCs of the study season had taken place (median dates). Then, using all of the present nine road districts as areal units, we determined if the beginning of the growing season and the median dates of MVCs were correlated. A total of 13,233 MVCs occurred during the study period. In every region, considering the selected 4-month annual period, the number of MVCs was the lowest in April but started to increase in May and was highest in June or July. The timing of the median dates for MVCs in all regions shifted to an earlier date and was positively correlated with the beginning of the growing season in every road district. We believe that the beginning of the growing season correlates with the timing of moose spring migration from wintering areas to summer pastures and further, with the timing of MVCs. Regardless of the ultimate reason behind our findings, we emphasize the practical importance of our results, namely how the onset of spring can help predict timing of spring MVCs. We recommend that warning campaigns informing road users coincide with the annually changing MVC season.     

Beavers promote calicioid diversity in boreal forest landscapes

Beavers are ecosystem engineers that modify and maintain a range of special habitat types in boreal forests. They also produce large quantities of deadwood that provide substrate for many lignicolous organisms such as calicioid fungi (Ascomycota). We studied how calicioid diversity differed between boreal riparian forests with and without beaver activity. The results show that calicioid diversity were significantly higher at beaver sites compared to the other two forest site types studied. The large quantity and diverse forms of deadwood produced by beavers clearly promotes calicioid diversity in the boreal landscape. The specific lighting and humidity conditions within beaver wetlands could be the reason why they promote the success of certain calicioid species.