I. 2006. Functional and numerical responses of four lemming predators in high arctic Greenland. Á/ Oikos 113: 193 Á/216.The high-arctic tundra ecosystem has the world's simplest vertebrate predator Á/prey community, with only four predators preying upon one rodent species, the collared lemming (Dicrostonyx groenlandicus ). We document the functional and numerical responses of all the four predators in NE Greenland. Using these data, we assess the impact of predation on the dynamics of the collared lemming with a 4 yr cycle and /100-fold difference between maximum and minimum densities. All predator species feed mostly (/90%) on lemmings when lemming density is /1 ha (1 , but the shapes of the predators' responses vary greatly. The snowy owl (Nyctea scandiaca ) is present and breeds only when lemming densities at snowmelt are /2 ha (1 , giving rise to a step-like numerical response. The long-tailed skua (Stercorarius longicaudus ) has a type III functional response and shifts from alternate food (mainly berries and insects) to lemmings with increasing lemming density. The skua surpasses all the other predators in summer by its total response. The type III functional response of the Arctic fox (Alopex lagopus ) starts to increase at much lower lemming densities than the responses of the avian predators, but it has only a weak numerical response. Finally, the stoat (Mustela erminea ) is the most specialized predator and the only one with a clearly delayed numerical response. According to their specific functional and numerical responses, each predator plays a key role at some point of the lemming cycle, but only the stoat has the potential to drive the lemming cycle. Stoat predation is greatly reduced in the winter preceding the lemming peak, and it reaches a maximum in the winter preceding the lowest lemming summer density. Stoat predation appears to maintain low lemming densities for at least two successive years. Our study provides empirical support for the specialist predator hypothesis about small mammal population cycles.
An area close to the Qinghai-Tibet plateau region and subject to intensive deforestation contains a large focus of human alveolar echinococcosis while sporadic human cases occur in the Doubs region of eastern France. The current review analyses and compares epidemiological and ecological results obtained in both regions. Analysis of rodent species assemblages within quantified rural landscapes in central China and eastern France shows a significant association between host species for the pathogenic helminth Echinococcus multilocularis, with prevalences of human alveolar echinococcosis and with land area under shrubland or grassland. This suggests that at the regional scale landscape can affect human disease distribution through interaction with small mammal communities and their population dynamics. Lidicker's ROMPA hypothesis helps to explain this association and provides a novel explanation of how landscape changes may result in increased risk of a rodent-borne zoonotic disease.
Sylvie DEBLAY, Dominique SALVI and Régis DEFAUT Giraudoux P., Pradier B., Delattre P., Deblay S., Salvi D. and Défaut R. 1995. Estimation of water vole abundance by using surface indices. Acta Theriologica 40: 77-96.A method to estimate the abundance of the fossorial form of the water vole Arvicola terrestris scherman (Shaw, 1801) has been developed, by using surface indices. Results are compared to the standard method of estimation using trap lines. These results show quantitatively that it is possible to differentiate reliably mole indices from water vole indices. Moreover, the two species are inclined to exclude each other. Even though water voles share the same galleries as moles, specific surface indices of the water vole occur for any density exceeding 2 ind/trap line (over 20 ind/ha). Several models of abundance estimation are put forward, all of them using linear multiple regressions. Correlations between the estimations from indices and the estimations from trap lines exceed 0.8 and the limits of using abundance classes are tested. Other limits are developed in the discussion. One of them is that the sampling intervals are saturated for densities exceeding 400 ind/ha. The index method, which is easy to carry out, offers the definite advantage of being suitable to space and time scales otherwise incompatible with estimations from trap lines. For instance, it allows distribution maps from wide transects about areas of more than 25 km 2 to be drawn, in less than two days.
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