Description:
Phenology, distribution and abundance of three Diptera species on Heard Island were investigated to provide baseline data for monitoring the effect on climate change on populations. Five vegetation types at two localities were sampled in two different years, firstly in the summer of 1987–1988 at Atlas Cove and secondly at Spit Bay over 12 months from summer 1992 to summer 1993. Pitfall traps and soil core extractions were operated in summer at both localities and pitfalls alone for 12 months from Spit Bay. The wingless Anatalanta aptera was the most abundant species in traps at Atlas Cove with most individuals collected from Poa tussock grassland, half as many from Pringlea and Azorella vegetation and fewest with a significantly higher level of asymmetry in the large katepisternal setae, from Azorella and Fellfield. Calycopteryx moseleyi was the most abundant fly in traps at Spit Bay, and A. maritima was the least abundant at both localities. Monthly pitfall catches from 1992–1993 indicated that A. aptera was active in most months of the year apart from winter, females early in the season and males active throughout the summer; teneral individuals only detected in January. C. moseleyi was more strongly seasonal with peak adult numbers occurring in January. Amalopteryx maritima was least seasonal in activity. Asymmetry in A. aptera suggests that it was at the limit of its ecological tolerance in Fellfield and Azorella on Heard Island. Changes caused by climate warming or invasive species are mooted.
Description:
Extinctions refer to the death of a single or multiple species (or taxon) and are common in the history of life on this planet. Using the fossil record, it has been estimated that 99.9% of the species that existed on earth is now extinct. Extinctions occur when a species fails to meet or adapt to changing environmental forces (such as global warming or cooling, habitat loss, destruction, or fragmentation) or when species origination is low, creating ecological niches for new, better adapted, species. This process of “background” extinction and new species evolution is natural, occurs continuously, and describes the way life diversified and radiated on this planet. However, when extinctions involve vast numbers of species and appear to occur around the same time in many different regions, as may be the case in modern times, they are termed “mass extinctions”; these are much less common, but greatly reduce species diversity. There is much debate and little consensus as to the cause and timescale of mass extinctions, generally referred to as the “Big Five” extinction events, which mark the point of transition to new geological epochs. This chapter will focus on the modern-day Holocene–Anthropocene extinction, which attributes the possible loss of up to 58,000 species per year to human activities.