Population cycles in the Greenlandic Collared Lemming (Dicrostonyx groenlandicus) in relation to food quantity and quality

Population cycles are closely related to Arctic ecosystems. Lemmings are common rodents in systems and characterised by extensive, regular population cycles of 4-5 years duration (Stenseth & Ims 1993). The collared lemming is the only rodent in Greenland. Through their effect on vegetation and on predator numbers they also affect the survival and reproductive success of many other organisms and therefore act as a key species in the simple terrestrial Greenlandic ecosystems. Their range of distribution in Greenland is within the High Arctic region in North and East Greenland. Cycles occur over extensive geographical areas, but may not be synchronously between geographically separated sub-populations.

Greenlandic Collared Lemming

The most important common mammalian and avian predators, ermine (Mustela erminea), arctic fox (Alopex lagopus), long-tailed skua (Stercorarius longicaudus), and snowy owl (Nyctea scandiaca) are in reproductive perspective highly dependant on the lemming abundance. Locally lemmings affect the cover, composition and flowering of the Arctic vegetation (Oksanen and Ericson 1987, Jefferies et al. 1992, pers. observation). The reasons for these cycles are poorly known, although a number of hypotheses exist.
Cycles being driven by social factors (stress) has been discussed and rejected by Boonstra and Boag (1992), nutritional quality of preferred food plants (Bryant et al. 1989, Seldal et al. 1994; Jefferies et al. 1992), predators (Sittler 1995), and others.

The main objectives of this project is to identify and analyse the importance of intra- and intertropic parameters affecting the collared lemming population dynamics and habitat use at Zackenberg, Northeast Greenland, with focus on plant-rodent-predator links. This project will be closely related to and draw upon data generated by the "Zackenberg Basic" monitoring programme initiated in 1995 (see attachment 1), as well as the long-term study on the same species at Karupelv, Traill Ø initiated in 1987 (Sittler 1994). Stress and parasites will not be considered in this project.

The main hypotheses under test are that:

· Plants through their nutritional state affect the quality and quantity of food available for lemmings as well as their habitat use during different stages of the population cycle.

· Snow distribution is the main parameter affecting the lemming's choice of winter habitat.

· Flowering in plant species utilised by lemmings is negatively correlated with lemming density. This may be explained by the recover strategy of the plants that may favour vegetative growths on behalf of reproductive growth.

The remaining part of the project concerns collection of basic information on the link between the four main predators and lemmings. In particular, the biology of the lemming population at the individual and population levels during different stages of the lemming cycles with respect to age and sex composition, reproductive status, morphology, feeding biology, and habitat use. During these analyses intratrophic dynamics will be considered. The project also aims to assess data on biomass km-2 of i) primary production of selected plant species relevant for lemmings, ii) lemming population and iii) predator population as well as their basal demands of energy will be assessed.