Backcasting and Forecasting Biological Invasions of Inland Lakes

Abstract

Abstract. Human introduction of nonindigenous species constitutes a serious threat to many ecosystems, particularly lakes. Recent attempts to predict invasions have focused on the supply of propagules of nonindigenous species to recipient ecosystems from source populations. Here we develop a spatially explicit ''gravity'' model to test this concept for Bythotrephes longimanus, a crustacean waterflea from Eurasia that is rapidly invading lakes in Ontario, Canada. The gravity model predicted spread of Bythotrephes based upon seven identified risk factors (e.g., use of contaminated fishing or boat anchor line) that may allow dispersal of either live individuals or their resting eggs from invaded to noninvaded lakes, as well as based on the spatial arrangement of invaded and noninvaded lakes in Ontario. Discriminant analysis of lake gravity scores successfully identified invasion status for 74% of 170 inland lakes. A retrospective analysis of 31 invaded lakes revealed that the order in which lakes were invaded was directly related to the magnitude of vector inflows from invaded sources. Analysis of the dominant vector inflow to each invaded lake revealed a ''stepping stone'' pattern in which at least five lakes were sequentially invaded from the source population in Lake Huron. One invaded lake (Muskoka) apparently served as an invasion ''hub,'' resulting in up to 18 additional direct and 17 indirect invasions. Species spread occurred via a combination of dominant, local diffusion (median distance 12.5 km) and rare, long-distance (Ͼ100 km) dispersal. Eleven of 131 lakes that were not invaded in 2000 were reported invaded in 2001. Gravity scores of these lakes were significantly higher than those of other noninvaded systems, indicating that susceptibility to invasion can be related to the magnitude of vector inflows. A GIS model based on gravity scores indicated that distribution of Bythotrephes is expected to expand to eastern and northwestern Ontario, although most new invasions are expected to occur in the central region of the province. Our results indicate that quantitative analysis of human dispersal vectors provides a robust starting point with which to assess vulnerability of discrete ecosystems to invasion. Management efforts focused on reducing the number and magnitude of human-mediated dispersal vectors may reduce the rate of invasion of new ecosystems.

Allee Effect and Control of Lake System Invasion

“…Examples of extracting the gravity model coefficients from invasions data can be found in [3,1,17]. For the sake of simplicity, in numerical experiments below we assume that m i = M i , and hence the transportation matrix is symmetric, T ij = T ji .…”

“…However, different configurations arise with different probabilities in course of invasion development. Studies of invasion histories show that the invader usually spreads along directions of the most active traffic from the invaded lakes [3,1,17], that is along connections with the biggest τ ij . Usually the number of such most probable invasion paths is much smaller than the total number of possible configurations.…”

“…The hardest problem is to estimate the total boat traffic. According to [3,1,17], in Wisconsin there are 58000 registered boaters, however only about 10% of boaters do long travels, including transfers of the boat from lake to lake. Each boater can make several travels per year, and lake system can cover several states, so eventually it seems reasonable to estimate T tot ∼ 10 5 boats/year, and in case of Wisconsin lake system one obtains ∼ 10 2 10 12 10 5 10 3 = 10 −8 1.…”

“…This can be described by the connectivity matrix, showing the intensity of the boat exchange between the lakes. Often the connection matrix can be approximated by so-called gravity models [27], which have been successfully applied to the problem of lake invasions by a number of authors [3,1,17].…”

Role of diapause in dispersal and invasion success by aquatic invertebrates

“…Natural vectors, such as fish (Jarnagin et al 2000) and waterfowl (Charalambidou et al 2003), can play a role in the dispersal of Bythotrephes resting eggs. However, in North America B. longimanus is mainly spread by boaters and anglers attached to equipment such as fouled fishing lines, boat anchor lines, downrigger cables, via infected bilge water and live well water, and live minnow bait which contain females bearing resting eggs (Jarnagin et al 2000;MacIsaac et al 2004). MacIsaac et al (2004) revealed that species spread occurred via a combination of dominant, local diffusion (median distance 12.5 km) and rare, long-distance (>100 km) dispersal.…”