Frank Adriaensen

The application of `least-cost' modelling as a functional landscape model

Abstract The growing awareness of the adverse effects of habitat fragmentation on natural systems has resulted in a rapidly increasing number of actions to reduce current fragmentation of natural systems as well as a growing demand for tools to predict and evaluate the effect of changes in the landscape on connectivity in the natural world. Recent studies used ‘least-cost’ modelling (available as a toolbox in GIS-systems) to calculate ‘effective distance’, a measure for distance modified with the cost to move between habitat patches based on detailed geographical information on the landscape as well as behavioural aspects of the organisms studied. We applied the method to a virtual landscape and a small scaled agricultural system subject to different scenarios in a land re-allotment project. We discuss the importance of technical aspects and ecological assumption underlying this modelling method. The model is shown to be a flexible tool to model functional connectivity in the study of the relation between landscape and mobility of organisms as well as in scenario building and evaluation in wild life protection projects and applied land management projects. Since ‘effective distance’ has the same units as Euclidean distance (m), this effective distance may be a straightforward way to include landscape and behavioural aspects in other models which include distance as a measure for isolation. We show the importance of the ‘ecological’ quality of the input maps and the choice of relevant landscape features and resistance values.

The design of artificial nestboxes for the study of secondary hole-nesting birds: a review of methodological inconsistencies and potential biases

Abstract. The widespread use of artificial nestboxes has led to significant advances in our knowledge of the ecology, behaviour and physiology of cavity nesting birds, especially small passerines. Nestboxes have made it easier to perform routine monitoring and experimental manipulation of eggs or nestlings, and also repeatedly to capture, identify and manipulate the parents. However, when comparing results across study sites the use of nestboxes may also introduce a potentially significant confounding variable in the form of differences in nestbox design amongst studies, such as their physical dimensions, placement height, and the way in which they are constructed and maintained. However, the use of nestboxes may also introduce an unconsidered and potentially significant confounding variable due to differences in nestbox design amongst studies, such as their physical dimensions, placement height, and the way in which they are constructed and maintained. Here we review to what extent the characteristics of artificial nestboxes (e.g. size, shape, construction material, colour) are documented in the ‘methods’ sections of publications involving hole-nesting passerine birds using natural or excavated cavities or artificial nestboxes for reproduction and roosting. Despite explicit previous recommendations that authors describe in detail the characteristics of the nestboxes used, we found that the description of nestbox characteristics in most recent publications remains poor and insufficient. We therefore list the types of descriptive data that should be included in the methods sections of relevant manuscripts and justify this by discussing how variation in nestbox characteristics can affect or confound conclusions from nestbox studies. We also propose several recommendations to improve the reliability and usefulness of research based on long-term studies of any secondary hole-nesting species using artificial nestboxes for breeding or roosting.

Incorporating landscape elements into a connectivity measure: a case study for the Speckled wood butterfly (Pararge aegeria L.)

In spatial studies of populations, Euclidean distance is commonly used to measure the structural connectivity between habitat patches. The role of the matrix on patch connectivity is thereby ignored. However, the importance of the matrix for (dispersal) movement is increasingly being acknowledged. Our study compared the cost-distance measure with the Euclidean distance. The cost-distance is a simple GIS-calculated connectivity measure that incorporates the resistance of the landscape matrix to movement behaviour. We used presence-absence data from a field study on the Speckled wood butterfly in two Belgian landscapes. Logistic regression revealed that the cost-distance measure had a significantly better predictive power than the Euclidean distance. This result was consistent for all the six sets of different matrix resistance values. In our study the cost-distance proves to be a better connectivity measure than the Euclidean distance.

Does matrix resistance influence Red squirrel (Sciurus vulgaris L. 1758) distribution in an urban landscape

In determining isolation effects in fragmented populations, the landscape matrix is not often considered. Usually simple distance measures are used to quantify degree of isolation. We tested the effect of the matrix on the presence of red squirrels in 354 wooded patches in the Brussels Region, by comparing several isolation measures. These were 1) distance to the nearest source patch, 2) the Hanski-measure (a combination of distance to and size of all possible sources), 3) effective distances calculated from different least cost models using the ArcView grid extension ‘Cost Distance’ (a combination of distance and resistance of the landscape, with different resistances for different landscape types) and 4) some combinations of the Hanski-measure and the effective distances. Size and quality of the target patches were always included in the tests of the predictive power of different isolation measures on squirrel presence/absence. All variables examined (patch size, quality and isolation) significantly influenced squirrel presence. Models using the effective distances gave the best results. Models including the Hanski-measure improved significantly when Euclidean distance was replaced by effective distance, showing that parameterisation of matrix resistance added significant additional explanatory power when modelling squirrel presence.

Density-dependent clutch size caused by habitat heterogeneity

In some studies but not in others the average clutch size decreases with density. We propose that density-dependent fecundity occurs because, as density increases, proportionally more poor-quality sites (with small clutches) are occupied, and not because the clutch size in all territories decreases. This mechanism will only cause density dependence if the habitat is heterogeneous at the scale of the home range or territory of an individual. Density-dependent fecundity will be found in some populations but not in others because of differences in the scale of habitat heterogeneity

Genetic Similarity, Inbreeding and Hatching Failure in Blue Tits: Are Unhatched Eggs Infertile?

We use data from a long-term population study in combination with DNA fingerprint data to study the frequency of inbreeding and its effects on reproductive parameters in a blue tit population. Close inbreeding was very rare in this population. The proportion of unhatched eggs in a clutch was related to the degree of genetic similarity between the parents as determined by multilocus DNA fingerprinting. Data from blue and great tit populations studied over 15 years show that about 25—30% of blue tit and 20 % of great tit nests contained at least one unhatched egg. The number or proportion of unhatched eggs in the nest was highly repeatable for pairs breeding in different years, but not for individual males or females. Unhatched eggs, therefore, were unlikely to result from functional infertility. The hypothesis that female blue tits engage in extra-pair copulations as insurance against their mate’s infertility can thus be discarded. Because the genetic similarity between the female and the extra-pair male was not lower than that between the female and her social partner, our data do not support the hypothesis that females engage in extra-pair copulations to reduce inbreeding depression.

Population dynamics and partial migration of the european robin (Erithacus rubecula) in different habitats

SUMMARY (1) We studied differences in habitat distribution, local survival and mating success • between the two morphs (resident/migrant) of the partially migratory European robin near Antwerp (Belgium). (2) Mean local survival of resident males (50%) was higher than local survival of migrant males (17%). During cold winters survival of residents decreased with about 50%. (3) Mating success decreased with settling date from 74% for early settling residents, over 44% for migrants to 19% for late-settling birds of unknown status. (4) The probability of breeding is two to four times higher in residents than in migrants. (5) Resident and migratory robins were habitat separated both in the breeding season and in winter: 70% of breeding males were migratory in the woodland, but in the park and gardens most males were resident. Almost all females were migratory. (6) Unbalanced reproductive success of the resident and migratory morphs and arguments for conditionality show that partial migration in the European robin is a conditional strategy in which the migrants are making the best of a bad job. (7) We explain why our conclusions do not contradict experimental evidence for a strong genetic influence on migratory tendencies in the European robin.

Dispersal distances of nuthatches, Sitta europaea, in a highly fragmented forest habitat

We studied dispersal distances of nuthatches in a highly fragmented landscape with only 2% of its area covered by suitable habitat (mature forest and parkland). We estimate that most surviving nestlings settled outside the 200-km 2 study area, and that mean dispersal distance was several times larger compared to more densely forested landscapes. However, local recruitment, defined as the proportion of nestlings settling within a small number of territories from the site of birth, did not differ between this study and other studies in large forests. Once young nuthatches had settled, they were less likely to move again in the fragmented landscape compared to large forests. We conclude that fragmentation causes an increase in natal dispersal distance but no discernible change in the number of territories between birth and establishment. However, fragmentation does effectively induce isolation once the young birds have settled

Causes and effects of divorce in the blue tit Parus caeruleus

1. Two hypotheses to explain why divorce in birds may be adaptive are the «incompatibility hypothesis» and the «better option hypothesis». At least two more, non-adaptive, hypotheses exist: the «accidental loss» and the «forced divorce» hypothesis. We propose a third non-adaptive hypothesis «the musical chairs hypothesis». 2. After making predictions to make it possible to distinguish between these hypotheses we analysed five blue tit Parus caeruleus populations. Divorce rates varied between 8 and 85%. 3. Birds that divorced laid significantly later and tended to have raised fewer young in the year before the divorce compared to pairs that stayed together. These latter did better than the population mean

Climate variation and regional gradients in population dynamics of two hole-nesting passerines

Latitudinal gradients in population dynamics can arise through regional variation in the deterministic components of the population dynamics and the stochastic factors. Here, we demonstrate an increase with latitude in the contribution of a large-scale climate pattern, the North Atlantic Oscillation (NAO), to the fluctuations in size of populations of two European hole-nesting passerine species. However, this influence of climate induced different latitudinal gradients in the population dynamics of the two species. In the great tit the proportion of the variability in the population fluctuations explained by the NAO increased with latitude, showing a larger impact of climate on the population fluctuations of this species at higher latitudes. In contrast, no latitudinal gradient was found in the relative contribution of climate to the variability of the pied flycatcher populations because the total environmental stochasticity increased with latitude. This shows that the population ecological consequences of an expected climate change will depend on how climate affects the environmental stochasticity in the population process. In both species, the effects will be larger in those parts of Europe where large changes in climate are expected.