PARENT SESSION
Thursday, August 10, 1:30-5:00 pm
COS 97 - Statistical ecology
L-4, Lobby Level, Cook Convention Center
Presiders: D Ford

Semivariance analysis of spatial patterns of abundance during range expansion for two invasive species: a test of theoretical predictions.

Maurer, Brian ^*,1, Nesslage, Genevieve¹, Gage, Stuart¹, ¹ Michigan State University, East Lansing, MI

ABSTRACT- Given the expectation that patterns of spatial autocorrelation in abundance are linked with geographic variation in population dynamics, we generated predictions of specific patterns of semivariance in abundances associated with different phases of range expansion. We tested these predictions using large scale data sets for two invasive species in eastern North America. Data on the spread of gypsy moths (Lymantria dispar) were obtained from a spatially extensive sample of pheromone traps in Michigan (USA) over a twelve year period (1985–1996). Data on the invasion of house finches (Carpodacus mexicanus) across eastern North America were obtained from yearly censuses conducted by the North American Breeding Bird Survey (BBS) over 25 years (1980–2004). For each data set we calculated annual semivariograms of population abundance. In both cases, we observed a progression from unimodal to linear to asymptotic variograms as the invasion progressed. These results are consistent with predictions from spatially explicit population models that include both demographic and dispersal processes. We conclude that spatial variation in abundance of species across geographic space is mechanistically explained by variation in local population dynamics and dispersal across spatially heterogeneous landscapes.

Key words: semivariance analysis, range expansion, invasive species