In this issue

Abstract

IN THIS ISSUE Bruce Osborne Overwintering Migrants Climate change has a number of indirect impacts aside from the well-described annual temperature increases, including an extension in the length of the growing season in many northern temperate regions. These changes in growing season length, including the earlier onset of growth in the spring and/or an autumn extension, have been well documented for many terrestrial plants but less is known about how these phenological changes impact on other organisms. Whilst there is evidence that migrant bird species may depart later in the autumn for their overwintering grounds, this is far from being a general phenomenon, as Donnelly et al., in this issue, point out. Their study, reported in this issue, assessed the length of time that migrant waterbirds spend in their wintering grounds on the East Coast of Ireland. Of the nineteen species examined, two arrived earlier, although none extended their period of stay, whilst temperaturerelated correlations between species and their duration of stay were not significant. So what are we to make of these results? As the authors point out, the analyses were hampered by the limited data set available, and this could have in turn limited any conclusions that could be drawn. The authors therefore argued that a more systematic approach to the study of the timing and departure of a wide range of migrant bird species is needed. Importantly, the results could indicate that any change to bird migration and overwintering patterns could be species-specific. Perhaps, also, the arrival and departure times of migrants could depend on other factors, such as food availability, which may also be dependent on phonologically related factors. This further highlights the complexity of understanding the effects of climate change at the ecosystem scale. Decline and fall of an introduced species There has been much discussion recently about the impacts of introduced or invasive species and their negative as well as positive benefits (see for instance the book review in this issue), with some seeing the increasing dominance of non-natives as an inevitable event. That they will eventually become a permanent fixture of the countryside is often assumed, although there is increasing evidence that these introductions are subject to the same dynamic fluctuations in population size that are sometimes seen for native species. Trowbridge et al., in this issue, describe post-boom declines in the population of the introduced seaweed Codium fragile in the Lough Hyne Marine Reserve, Co. Cork. Introduced to these islands in the 1800’s C. fragile is often regarded as one of the more significant algal invaders, although population declines have been noted previously. Investigations by Trowbridge et al. indicated that the population decline observed in Lough Hyne was associated with both low reproduction and/or survival. As to the cause of these changes in survival or reproduction rates, neither grazing by limpets or sea urchins appeared to be involved, despite the evidence provided by early studies. In a wider context these results are important in providing further evidence that introduced or invasive populations may only be successful in the short-to-medium term in some locations and further studies are required to better understand the factors contributing to both the success and failure of alien species. Perhaps the factors contributing to the early establishment and success of introduced species are different from those that contribute to the longer term persistence of species within a community? Otter distribution Regarded as one of the most threatened aquatic mammals of freshwater ecosystems in Europe, the otter (Lutra lutra) is still relatively widespread in Ireland, with little evidence of any significant longterm reduction in numbers or distribution. This is somewhat surprising given that reductions in water quality and changes in landscape ecology that have been associated with the decline of this species in Europe have also occurred to a similar extent in Ireland. There is, however, a concern that the apparently improved status of otters in Ireland may be simply a result of improved information gathering rather than reflecting any real increase or the maintenance of existing numbers. It is against this backdrop of uncertainty that Patrick Smiddy, in this issue, surveyed the distribution of the otter in the Munster...