Harto Lindén

Synchrony in Population Dynamics

Our data are long-term population dynamics of a set of species in different localities in Finland. There is considerable level of species-specific synchrony in population fluctuations among the localities. The degree of synchrony levels off with increasing distance among the populations compared. Climatic perturbations and dispersal have been proposed as pace-making factors for synchrony. According to Moran’s theorem, local populations sharing a common structure of density dependence should become synchronized under the influence of a spatially correlated density-independent factor. This predicts synchrony to decay slower with increasing distance between local populations than if the synchrony is caused by dispersal. To explore the significance of the Moran effect and dispersal in explaining the observed regional synchrony, we used a metapopulation system. The Moran effect and dispersal are both capable to synchronize alone local population fluctuations. However, with dispersal the level of synchrony decreases with distance among the populations. Adding Moran’s effect does not greatly affect the level of synchrony, nor the negative correlation between synchrony and distance. This finding makes it difficult to tell apart whether an observed negative correlation between the level of synchrony and distance among the compared populations is caused by dispersal alone, or both dispersal and Moran’s effect acting together.

LANDSCAPE FRAGMENTATION AND FOREST COMPOSITION EFFECTS ON GROUSE BREEDING SUCCESS IN BOREAL FORESTS

We examined the breeding success of forest grouse in relation to anthropogenic forest fragmentation in Finland. Employing Geographic Information Systems (GIS) and grouse data derived from Finnish wildlife triangle censuses conducted during 1989–1994, we combined the locations of 2267 Black Grouse (Tetrao tetrix) and 1060 Capercaillie (T. urogallus) females after the breeding season in mid-August with landscape data. The indicators of breeding success were the proportion of grouse hens with a brood and brood size. Two study areas (each 45 000 km2) in the boreal zone were selected for investigation. The breeding success of grouse was negatively correlated with both fragmentation of forest area per se by farmland and the decreasing proportion of older forest as a result of clear-cutting. The extent of landscape accounting best for variation in nesting success was an order of magnitude larger (∼100 km2) than the area most probably used by a grouse female and her brood during the summer, which suggests that la...

Abundances of red fox and pine marten in relation to the composition of boreal forest landscapes.

The effects of human-caused fragmentation of boreal forest on the abundance of red fox Vulpes vulpes L. and pine marten Martes martes L. were studied by combining the Finnish wildlife-triangle snow-track data (1990-94) with land-use and forest resources data employing the GIS. Two study areas (each 45 000 km(2) ) located in northern and southern Finland were selected for the investigation. The extent of landscape that best explained predator abundance (tracks per 10 km 24 h(-1) ) was the same (about 100 km(2) ) in both species and study areas. The decreasing proportion of older forest and the increasing proportions of young forest and agricultural land in the landscape positively affected track density of red fox. The relationship between agricultural land and fox abundance, however, was characterized by a convex curve peaking at 20-30% of agricultural land. With the habitat classification used, landscape composition explained 26% and 11% of the spatial variation in fox abundance in the northern and southern study area, respectively. The relationship between landscape composition and pine marten abundance was not as clear as in that of red fox. Landscape composition explained 10% and 6% of spatial variation in pine marten abundance in the northern and southern study area, respectively. In both areas a positive impact occurred with the increasing proposition of young forest in the landscape, but in the northern area the negative effect of increasing proportion of agricultural land was dominant. The abundances of red fox and pine marten were not negatively correlated, indicating that competition or intraguild predation by red fox do not determine abundance of pine marten on a landscape scale. A general increase in predation pressure by generalist predators in fragmented forest landscapes has been an intensively discussed conservation problem during recent years. We conclude that the red fox is a species potentially able to cause elevated predation pressure in boreal landscapes fragmented by human activities, but that the evidence against the pine marten is weaker.

Synchrony in Tetraonid Population Dynamics

We studied temporal and spatial synchrony of population fluctuations in the capercaillie (Tetrao urogallus), the black grouse (Tetrao tetrix) and the hazel grouse (Bonasa bonasia) in Finland. The data consist of route censuses (20 000-30 000 km annually) performed in 11 provinces during 1964-83. The population data for the three species in each province were standardized to zero mean and unit variance. Cross-correlation analysis indicates that population dynamics of the three species in every area are in rather good temporal synchrony. Moreover, with the aid of k-means clustering, the 11 provinces could be merged into four regions, indicating large-scale synchrony in dynamics of the three tetraonid species. Because it is obvious that this synchrony cannot be due only to the similar life histories of these species, we explored whether it could be influenced by a common synchronizing factor affecting all the species simultaneously. In order to do this we used a Leslie matrix-based simulation approach. In this model there is a stochastic hit of breeding failure at a given average interval. This failure was shown to synchronize the population dynamics of the species with primarily different life tables.

Short- and long-term population dynamical consequences of asymmetric climate change in black grouse

Temporal asymmetry in patterns of regional climate change may jeopardize the match between the proximate and ultimate cues of the timing of breeding. The consequences on short- and long-term population dynamics and trends as well as the underlying mechanisms are, however, often unknown. Using long-term data from Finland, we demonstrate that black grouse (Tetrao tetrix) have responded to spring warming by advancing both egg-laying and hatching. However, early summer (the time of hatching) has not advanced, and chicks have to face colder post-hatching conditions. Demonstrating that these conditions are critical to post-hatching survival, we show that chicks are increasingly suffering higher mortality because they hatch too early. Consequently, breeding success and population size has severely declined over the past four decades. Finally, we modelled the impact of this particular climate change scenario on population dynamics and show that the mismatch can further explain the observed collapse of cyclic fluctuations. Because the evolutionary response of grouse is lagging behind the novel selective pressures, seasonally asymmetric climate change is likely to constitute an important determinant of future short- and long-term changes in the dynamics of black grouse populations.

Latitudinal Gradients in Predator-Prey Interactions, Cyclicity and Synchronism in Voles and Small Game Populations in Finland

Finnish game questionnaire data from 1964-83 have been used to study cyclicity and the synchronism between species in population fluctuations of voles and 10 small game species. All the species are cyclic in at least some provinces. The most clearly cyclic species are black grouse and hazel grouse, with 6-7 yr cycles. Stoat, weasel and voles are representatives of the 3-4 yr type. The observed cycle lengths are concentrated in years four and seven. The degree of cyclicity is much higher in northern Finland than in southern provinces. The fluctuations of predators and their prey are not simultaneous. However, there is synchronism between ecologically similar species or synchronism (with time lag) between a predator and its prey. The relatively weak synchronism of voles to other species, the disharmony in the distribution of cycle lengths and the contradictory predator-prey relationships suggest that the alternative prey hypothesis cannot explain the origin of, for instance, tetraonid cycles.

Large-scale synchrony in the dynamics of capercaillie, black grouse and hazel grouse populations in Finland

We analysed 1964-1983 data on population numbers of capercaillie, black grouse and hazel grouse in 11 provinces in Finland. The three species are known to display cyclic dynamics with a periodicity of approximately six yr. Synchrony in species-specific population fluctuations was scored by calculating cross correlations with zero lag among all the provinces. Provincial data were also used to assess the relation between climatic factors and synchrony in the population fluctuations. To enable the statistical analysis, the number of the 12 climate variables was reduced to three non-correlating principal components. A bootstrap method was used both for parameter estimation and for assessing statistical significance level when comparing the tetraonid synchrony with the climate data. For all three species we found large-scale synchrony in population fluctuations. The level of synchrony decreased, however, with geographical distance among the provinces. When a partial correlation analysis is done correcting for the weather-derived principal components, correlations with synchrony and distance remained with two of the three principal components. When corrected for distance, there is correlation between synchrony and climate for capercaillie and black grouse. We conclude that spatial phenomena, such as climatic homogeneity within closely located areas and dispersal of individuals are responsible for maintaining large-scale synchrony.

Capercaillie Tetrao urogallus - a good candidate for an umbrella species in taiga forests

The capercaillie Tetrao urogallus is widely accepted as a species seriously suffering from fragmentation of forests and habitat loss. Foresters as well as conservationists agree on the need and principles for maintaining viable populations, but the proposed management means often differ. The approach currently favoured by Finnish foresters is to manage capercaillie leks and their surroundings using methods that differ from those used in intensive forestry. It may be desirable to prove that forests with capercaillie leks also favour other forest bird species and biodiversity in general. During the last 16 years (1987–2002), forest birds have been censused and capercaillie leks were mapped in the 465-km2 study area in southern Finland. Most of the study area consists of spruce-dominated mature forests. The remainder of the landscape is a mixture of variously aged forests, agricultural areas, lakes and scattered human settlements with a gradient from an agricultural-forest mosaic to forest-dominated areas. The old-growth forest bird species three-toed woodpecker Picoides tridactylus, pygmy owl Glaucidium passerinum and red-breasted flycatcher Ficedula parva were more abundant within 300 m and 1,000 m radii around capercaillie lek sites than in non-lek control sites. Also the overall species richness of breeding forest birds was higher in the vicinity of capercaillie leks. On a larger scale (100 × 100 km squares), using the wildlife triangle scheme developed in Finland, we show that the density of capercaillie closely coincides with a wildlife richness index describing the total abundance of 15 other forest-dwelling mammal and bird species with diverse ecology and habitat requirements. Capercaillie is a flagship species for foresters, and can be considered a good candidate for an umbrella species for wildlife in taiga forests.

Large-scale forest corridors to connect the taiga fauna to Fennoscandia.

Finland and Russian Karelia belong to the same biogeographical entity, lying on the same Precambrian bedrock. During the last half century there has been an enormous ‘natural experiment’, in which forestry in Finland has been very intensive, whereas in Karelia forestry has been negligent leaving large primaeval areas untouched. As a result, Russian forests have a much greater diversity of wildlife. In particular, rare species and species favouring old forests are more abundant in Karelia than in Finland. Typical dominant species in Finland are those characteristic of younger successional stages as well as many vole-dependent small carnivores. Finland is situated on the eastern margin of a vast coniferous taiga. The future of the taiga fauna in Fennoscandia is dependent on the condition of the taiga forests in Russia and on the connectivity of Fennoscandian forest areas to the intact taiga, i.e. connectivity at the border between Russia and Finland. In this paper, we focus our attention on the narrow isthmus between the White Sea and Lake Onega, which is an extremely important connection for the northern element of the taiga fauna. The capercaillie Tetrao urogallus may be a good focal species, with its large spatial requirements for lek areas depicting the need for connectivity to maintain viable populations. We suggest that large-scale connections should be planned, ‘forest bridges’ intruding into Finland and even into Sweden, where the proportion of mature forests would be high enough (as much as ⅓ of the total area) to guarantee the connectivity between subpopulations. We argue that this may not necessarily represent additional costs for forestry, provided that actions are taken for a careful large-scale planning of forest harvesting to satisfy the requirements of these corridors. We believe that large-scale preservation of ecosystems will be a better strategy in the future than species-specific conservation programmes for wildlife species.

The Clockwork of Finnish Tetraonid Population Dynamics

We studied 1964-1983 population dynamics of three species of tetraonids, capercaillie (Tetrao urogallus), black grouse (Tetrao tetrix) and hazel grouse (Bonasa bonasia) in Finland. The data comprise species-specific quantitative estimates of bird numbers in 11 provinces during the 20-yr period. Autocorrelation functions calculated from the trend-corrected data suggest that the population fluctuations are cyclic in all three species, cycles most frequently displaying six-yr periodicity. A model acknowledging long-term trend and incorporating linear combination of sine and cosine transforms of time mimics the fluctuations reasonably well. The coefficients of determination ranged from 25% to 88% depending on species and province. Fitting the same model to 1897-1930 hunting statistics of black grouse from south-western Finland indicates that such a clockwork-like dynamics has been ticking at least from the beginning of this century. An analysis of variance of the lengths of increase and decrease phases of the population cycles further confirm the symmetric regularity of the tetraonid dynamics. No differences were found among species or provinces. A theoretical analysis, based on projection matrix techniques, shows that it is unlikely that such a regular cyclicity could be driven solely by intrinsic components of the population structure. The domain of other possible factors responsible for the clockwork-like dynamics is explored.