A meta-analysis of the effects of habitat loss and fragmentation on genetic diversity in mammals

Assessing the role of local populations in a landscape context has become increasingly important in the fields of conservation biology and ecology. A growing number of studies attempt to determine the source-sink status of local populations. As the source-sink concept is commonly used for management decisions in nature conservation, accurate assessment approaches are crucial. Based on a systematic literature review of studies published between 2002 and 2013, we evaluated a priori predictions on methodological and biological factors that may influence the occurrence of source or sink populations. The review yielded 90 assessments from 73 publications that included qualitative and quantitative evidence for either source or sink population(s) for one or multiple species. Overall, sink populations tended to occur more often than source populations. Moreover, the occurrence of source or sink populations differed among taxonomic classes. Sinks were more often found than sources in mammals, while there was a non-significant trend for the opposite to be true for amphibians. Univariate and multivariate analyses showed that the occurrence of sources was positively related to connectivity of local populations. Our review furthermore highlights that more than 25 years after Pulliam's widely cited publication on 'sources, sinks, and population regulation', in-depth assessments of the source-sink status of populations based on combined consideration of demographic parameters such as fecundity, survival, emigration and immigration are still scarce. To increase our understanding of source-sink systems from ecological, evolutionary and conservation-related perspectives, we recommend that forthcoming studies on source-sink dynamics should pay more attention to the study design (i.e. connectivity of study populations) and that the assessment of the source-sink status of local populations is based on λ values calculated from demographic rates.

Empirical evidence for source-sink populations: a review on occurrence, assessments and implications.

We analyzed the responses of small mammals to clear-cutting in temperate and boreal forests in Europe. We conducted a meta-analysis of published research on most often studied small mammal species (the striped field mouse, the yellow-necked mouse, the wood mouse, the field vole, the common vole, the bank vole, the Eurasian harvest mouse, the common shrew and the Eurasian pygmy shrew), comparing their abundance on clear-cuts and in unharvested stands. For four other species (the gray-sided vole, the Siberian flying squirrel, the Eurasian red squirrel and the hazel dormouse), we provide a qualitative review of their responses to forest harvest. Results of the meta- analysis suggest that common species of small mammals usually increase in abundance after clear-cutting or are unaffected by this disturbance. As an exception, the yel- low-necked mouse declines after clear-cutting in boreal but not in temperate forest. The qualitative review suggests that the responses of more specialized (e.g., arboreal) species to forest harvest are more varied than the responses of generalist species included in the meta-analysis. For some species of small mammals (e.g., the Siberian flying squirrel), habitat loss resulting from forest harvest is a major threat.

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Responses of small mammals to clear-cutting in temperate and boreal forests of Europe: a meta-analysis and review

Conservation of species requires knowledge on population changes in time, but achieving such data in proper spatio-temporal scales can often be difficult for rare and vulnerable species. We used long-term (1950-2005) diet data of three avian predators (the nocturnal Ural and eagle owls and the diurnal goshawk) from four landscapes to study population changes of two forest-dwelling species, the Siberian flying squirrel Pteromys volans and the red squirrel Sciurus vulgaris in Finland. We also determined the role of vulnerable flying squirrel in the diet of these predators. Both squirrel species were relatively rare in the diets of the three avian predators, with the exception of red squirrel in the diet of goshawks. The Siberian flying squirrel also appears to be a less important prey for avian predators than flying squirrel species (Glaucomys spp.) are in North American forest communities. Numbers of consumed flying squirrels, but not of red squirrels, increased as the abundances of voles increased in the diets of eagle and Ural owls, that is more flying squirrels were consumed during the good vole years than the poor ones. The declining trends in the diets of three avian predators appeared to be quite similar for both studied squirrel species, possibly indicating that the process behind the decline has been the same.

Decline of flying and red squirrels in boreal forests revealed by long-term diet analyses of avian predators

Ineffective enforced legislation for nature conservation: A case study with Siberian flying squirrel and forestry in a boreal landscape

Habitat loss is the major phenomenon threatening species in the boreal forests. One example of a threatened species affected by habitat loss is the Siberian flying squirrel (Pteromys volans). We used mark-recapture data from 1992 to 2004 for 3 flying squirrel populations to estimate the demographic parameters of these populations. Average adult survival was 0.43-0.53, and probability of surviving and staying near the natal territory through the first winter was 0.23-0.30 in different populations. These values are low compared to survival estimates presented in the literature for other Sciurid species. The estimated population growth rates indicated population decline in all areas. In one of the areas, we found a decline in adult survival and population growth rate during the study. This decline was demonstrated to be linked to ongoing habitat loss due to logging. Low survival and emigration probabilities suggest that these populations are likely to be sinks. This highlights the need to ensure dispersal between the remaining patches of suitable habitat for successful conservation of this and other species associated with old-growth forests. The situation is worrisome as the studied populations are situated in an area where flying squirrel population densities have traditionally been high. Keywords: habitat loss, mark-recapture, source-sink. Resume : La perte d'habitat est la cause principale qui menace les especes des forets boreales. Un exemple d'une espece menacee par la perte d'habitat est le polatouche de Siberie, Pteromys volans. Nous avons utilise des donnees de marquage- recapture de 1992 a 2004 pour 3 populations de polatouches afin d'evaluer les parametres demographiques de ces populations. La survie moyenne des adultes etait de 0.43-0.53 et la probabilite de survie et de presence pres du territoire natal apres le premier hiver etait de 0.23-0.30 dans differentes populations. Ces valeurs sont faibles en comparaison avec les valeurs estimees presentees dans la litterature pour la survie d'autres especes de sciurides. Les taux de croissance demographique estimes indiquaient un declin des populations dans tous les secteurs. Dans un des secteurs, nous avons trouve une baisse de la survie des adultes et du taux de croissance demographique au cours de l'etude. Il a ete demontre que ce declin etait lie a la perte d'habitat en cours causee par la coupe forestiere. La faible survie et les probabilites d'emigration suggerent que ces populations sont probablement des puits. Cela met en evidence la necessite d'assurer la dispersion entre les parcelles restantes d'habitat approprie pour le succes de conservation de cette espece ainsi que d'autres associees aux forets anciennes. La situation est inquietante puisque les populations etudiees sont situees dans un secteur ou les densites de population de polatouches etaient traditionnellement elevees. Mots-cles : marquage-recapture, perte d'habitat, source-puits.

https://bioone.org/journals/ecoscience/volume-16/issue-1/16-1-3184/Survival-and-Population-Growth-Rate-of-the-Threatened-Siberian-Flying/10.2980/16-1-3184.pdf

Survival and Population Growth Rate of the Threatened Siberian Flying Squirrel (Pteromys volans) in a Fragmented Forest Landscape

To devise effective conservation actions, it is important to know which factors are associated with the population parameters of a declining population. Using mark–recapture methods, we estimated the annual population size, growth rate and survival probability of an ear-tagged flying squirrel population over a 15-year period in a 4,500 ha study area in western Finland. The species is considered vulnerable, but detailed knowledge concerning population sizes or trends is lacking. The population parameters and changes therein were regressed against habitat availability, an indicator of predation pressure, and mean winter temperature (an indicator of climate change), to reveal potential reasons for trends in the population. The best-fit models suggested the annual growth rate to be below one, and on average it was 0.93 (±0.06; SE) across the 15-year period. The survival probability was about 0.22 (±0.03) for juveniles and 0.50 (±0.03) for adults. The population size of adult flying squirrels decreased from 65 (±11) individuals in 1995 to 29 (±6) individuals in 2009. The number of flying squirrels was associated with the amount of available habitat, but the decline in population size was more rapid than the loss of habitat area. If the current decreasing trend in habitat availability continues, the population might become extinct by the year 2020. To halt the population decline, it is necessary to refrain from clear-cutting mature spruce stands until new suitable habitats develop from the maturation of younger forests.

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Are habitat loss, predation risk and climate related to the drastic decline in a Siberian flying squirrel population? A 15 year study

Accurate estimates of population size and distribution are a prerequisite for effective management of populations, but for most species a reliable estimation of the absolute population size is very difficult. In 1998, the Finnish Ministry of Environment set up a working group to plan a national-level survey for estimation and monitoring of the population size of Siberian flying squirrel (Pteromys volans). In 2006, the population size was reported to be 143 000 females. However, evaluation of the magnitude of possible biases was not attempted. Our aim was to test the population size estimate by conducting a resampling study with the methods of the national survey on an eartagged population of flying squirrels. We found that the methods used in the national survey provide greatly upward biased estimates. Moreover, the magnitude of the bias in the method seems to be sensitive to the true population sizes rendering the method unsuitable for population trend monitoring purposes. Therefore, we caution against u...

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Difficulty of Getting Accurate and Precise Estimates of Population Size: The Case of the Siberian Flying Squirrel in Finland

Climatic conditions, trophic links between species and dispersal may induce spatial synchrony in population fluctuations. Spatial synchrony increases the extinction risk of populations and, thus, it is important to understand how synchrony-inducing mechanisms affect populations already threatened by habitat loss and climate change. For many species, it is unclear how population fluctuations vary over time and space, and what factors potentially drive this variation. In this study, we focus on factors determining population fluctuations and spatial synchrony in the Siberian flying squirrel, Pteromys volans, using long-term monitoring data from 16 Finnish populations located 2–400 km apart. We found an indication of synchronous population dynamics on a large scale in flying squirrels. However, the synchrony was not found to be clearly related to distance between study sites because the populations seemed to be strongly affected by small-scale local factors. The regularity of population fluctuations varied over time. The fluctuations were linked to changes in winter precipitation, which has previously been linked to the reproductive success of flying squirrels. Food abundance (tree mast) and predator abundance were not related to population fluctuations in this study. We conclude that spatial synchrony was not unequivocally related to distance in flying squirrels, as has been observed in earlier studies for more abundant rodent species. Our study also emphasises the role of climate in population fluctuations and the synchrony of the species.

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Antero Mäkelä

Papers

Survival and Population Growth Rate of the Threatened Siberian Flying Squirrel (Pteromys volans) in a Fragmented Forest Landscape

Are habitat loss, predation risk and climate related to the drastic decline in a Siberian flying squirrel population? A 15 year study

Difficulty of Getting Accurate and Precise Estimates of Population Size: The Case of the Siberian Flying Squirrel in Finland

Population fluctuations and spatial synchrony in an arboreal rodent.