Postflood movements and population connectivity in gambusia (Gambusia holbrooki)

A population of the exotic pest fish Gambusia holbrooki inhabiting a drainage channel was sampled regularly to record responses to flooding and subsequent population reestablishment. The flood reduced numbers in the channel to near-zero levels. After remaining very low for 2 months, densities increased steadily through juvenile recruitment and the concentration of fish in drying pools. Tagging revealed that in general, movements between pools separated by only a few metres were relatively limited. There was evidence for habitat segregation and population subdivision, as fish from different pools varied markedly in terms of mean population density, movement behaviour, sex and size composition and juvenile recruitment. The most favoured pool was relatively deep, well lit and had the greatest habitat diversity. Gambusia control measures are likely to be most effective if timed to coincide with floods (which reduce local population densities) and/or droughts (which concentrate fish and allow targeting of source populations)

Documenting lemming population change in the Arctic: Can we detect trends?

Lemmings are a key component of tundra food webs and changes in their dynamics can affect the whole ecosystem. We present a comprehensive overview of lemming monitoring and research activities, and assess recent trends in lemming abundance across the circumpolar Arctic. Since 2000, lemmings have been monitored at 49 sites of which 38 are still active. The sites were not evenly distributed with notably Russia and high Arctic Canada underrepresented. Abundance was monitored at all sites, but methods and levels of precision varied greatly. Other important attributes such as health, genetic diversity and potential drivers of population change, were often not monitored. There was no evidence that lemming populations were decreasing in general, although a negative trend was detected for low arctic populations sympatric with voles. To keep the pace of arctic change, we recommend maintaining long-term programmes while harmonizing methods, improving spatial coverage and integrating an ecosystem perspective