High Risk Of Local Extinction Research Articles

Evolutionary potential but not extinction risk of Lahontan cutthroat trout (Oncorhynchus clarkii henshawi) is associated with stream characteristics

Habitat fragmentation represents a major extinction threat for species of all taxa. Isolated populations have a higher risk of local extinction because of environmental variability and demographic processes associated with small populations. Here we examine the relationships among isolation, habitat size, habitat characteristics and variability, and genetic effective population size with extinction risk for 10 isolated and three interconnected populations of Lahontan cutthroat trout ( Oncorhynchus clarkii henshawi ) sampled from throughout their range. Contrary to expectations, we did not find a relationship between most habitat variables and extinction risk. However, we did find strong relationships between habitat variables and genetic effective population size, including a significant negative correlation between pool density and effective population size. Small effective population sizes can result in reduced genetic variation and losses of evolutionary potential and adaptability to changing environments. The absence of strong habitat correlates with extinction risk — despite an observed relationship with effective population size — highlights the need to consider habitat diversity at multiple spatial scales when considering management scenarios to both promote population persistence and maintain evolutionary relevance.

Phenetic population structure of the land snail Helix albescens (Gastropoda, Pulmonata, Helicidae) in the Crimea

The polymorphism of shell banding pattern has been studied in Crimean populations of the land snail H. albescens. The results show that snails from different regions of the Crimea are characterized by specific types of shell polymorphism, the differences between them concerning mainly the number of observed shell morphs rather than their occurrence frequency. In particular, the proportion of snails with darkly colored shells increases in relatively cool habitats. However, among the microevolutionary processes determining the type and degree of polymorphism in H. albescens populations, a major role is also played by stochastic genetic phenomena, because the species exists in semi-isolated colonies with low effective abundance and high risk of local extinction.

Habitat quality predicts the distribution of a lizard in fragmented woodlands better than habitat fragmentation

AbstractOrganisms often face a higher risk of local extinction in fragmented than in continuous habitat. However, whether populations are affected by reduced size and connectivity of the habitat or by changes in habitat quality in fragmented landscapes remains poorly investigated. We studied the regional distribution and microhabitat selection of the lacertid lizard Psammodromus algirus in a fragmented landscape where the existence of deciduous and evergreen woodlands brought about variation in habitat quality. Lizards never occupied any fragment smaller than 0.5 ha. However, above that limit fragment size no longer predicted lizard occurrence, which was explained by woodland type instead, with lizards being more frequently found in deciduous than in evergreen woodlands. Lizards selected microhabitats that had structural features favouring thermoregulation, foraging and predator avoidance, and we identified better conditions for thermoregulation and food acquisition in deciduous than in evergreen woodlands. Our results support the idea that variation in habitat quality can sometimes override the effect of habitat fragmentation on animal populations. We consider the implications of our study for the conservation of Mediterranean lizards, discussing our results in a broader context framed by previous studies conducted in nearby areas.

A model for the effects of fire and fragmentation on the population viability of the Splendid Fairy-wren

Computer simulation was used to model the relationships between four environmental factors (nest predation, brood parasitism, fire and rainfall) and the probability of local extinction in hypothetical populations of Splendid Fairy-wrens in differently sized patches of habitat. The parameters of the model are based on the results of a long-term (17 year) study of the species at Gooseberry Hill, Western Australia. Two fire scenarios are modelled ? wildfire and controlled burning. The model predicts that wren populations in small patches (less than about 2 000 ha in area) stand a high risk of local extinction if exposed to environmental conditions similar to those experienced at Gooseberry Hill, in particular the frequency and extent of wildfires (Gooseberry Hill fire probability 20%). It is suggested that: (a) urban reserves aimed at conserving small sedentary species such as the Splendid Fairy-wren should contain at least 2 000 ha of suitable habitat if there is a high risk of wildfire (minimum viable population for wrens under these conditions, 500 breeding females); (b) the integrity of existing reserves and parklands should be protected from further fragmentation since the likelihood of local extinctions will increase as the carrying capacity of the habitat declines; (c) management of existing reserves and parklands should be directed toward limiting the environmental pressures impacting populations of native species, in particular the frequency and extent of fire and the numbers of feral nest predators. If the probability of fire can be limited to five per cent or less, Splendid Fairy-wren populations in patches as small as 400 ha (100 breeding females) may be viable in the long term.