Abstract:Temperatures within soil and plant habitats on Signy Island in the maritime Antarcticwere measured during 1987. Four sites were monitored using minithermistors attached to a data logging system. Three main periods within the annual temperature cycle were identified. In springhummer (November-March) there was much inter-day variation in maximum temperatures, but minimum daily temperatures were always close to 0°C. However, there were very few freeze-thaw cycles extending below the -0.5"C threshold during this period, and those that occurred were not severe. It is considered that freeze-thaw cycling is unlikely to be a significant factor in organism survival during summer. All sites showed a long period of relatively mild subzero temperatures during autumn (March-May). This may be of importance in promoting cold-hardiness of organisms living in these ecosystems before the decline to lower winter temperatures. Minimum winter temperatures varied markedly between sites; lowest temperatures occurring in areas where there was little insulating snow cover. Within site temperature variation was generally small, confirming the validity of the use of small numbers of probes to monitor environmental temperatures in such habitats.

1. The effects of prey density and temperature on the feeding and development rates of several late instars of the larvae of three common European damselflies (Lesres sponsu (Hansemann), Coenagrion puella (L.) and Ischnuru eleguns van der Linden) were investigated in a laboratory experiment.2. Functional responses were used to estimate maximum feeding rates. Maximum feeding rates were compared.between species, instars and temperatures by expressing prey consumption in tenns of prey biomass consumed per unit predator biomass. Lesres was capable of feeding at almost twice the rate of either Coenagrion or Zschnuru.3 . Higher feeding rates led to faster development rates and there was an interaction between species and temperature. With the exception of those with very low feeding rates, larvae maintained at higher temperatures, but similar feeding rates, developed faster. Under similar conditions of temperature and feeding rate, Lesres larvae developed faster than larvae of either Coenagrion or Ischnuru.4. Faster development rates at similar rates of food intake were achieved at the cost of reduced size-increases between instars.5 . The differences in the responses of the three species are discussed in the light of their respective life histories, and with reference to a recent model of population regulation in damselflies.Cambridge -3 OET.nents. The predator rate of increase is determined by the survival and development rates of the predator, and by its fecundity.This study examines one subcomponent of the predator rate of increase, namely the development rate. It does this using a laboratory simulation of a temperate freshwater predator/ prey system, that of zygopteran larvae and their prey. In Britain zygopteran populations are frequently univoltine, so that changes in survival IF17

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