Environmental factors influencing invasibility and ecological consequences of persistent invasions of the spiny waterflea

摘要

The spiny waterflea, Bythotrephes longimanus (Crustacea: Onychopoda: Cercopagidae), is a predatory zooplankter native to Eurasia that has invaded more than 80 lakes in North America over the last 3 decades. Its inconsistent invasion pattern - high success in some lakes and absence in other proximal lakes (MacIsaac et al. 2000, Branstrator et al. 2006) - undoubtedly results from variation in regional dispersal and local habitat (Shurin 2000). However, teasing apart the relative importance of these processes is difficult because dispersal vectors remain poorly defined (Branstrator et al. 2006), habitat requirements are not fully understood (MacIsaac et al. 2000, Branstrator et al. 2006), and the invasion record is incomplete. In a series of reservoirs in St. Louis County, Minnesota (USA), local habitat, not regional dispersal, has likely limited establishment. Island Lake Reservoir, Fish Lake Flowage, and Boulder Lake were invaded in the 1990s (Forman & Whiteside 2000), when presumably planktonic animals and/ or diapausing eggs were transported from previously invaded Lake Superior. B. longimanus persisted in Island Lake Reservoir (hereafter Island Lake), but failed to establish in Fish Lake Flowage (hereafter Fish Lake) and Boulder Lake (Forman & Whiteside 2000, Branstrator et al. 2006). Insufficient abiotic and/or biotic habitat in Fish Lake and Boulder Lake may have prevented establishment of B. longimanus; the exotic is sensitive to extremes in temperature, salinity, pH, and dissolved oxygen (Grigorovich et al. 1998, Brown 2008) and also requires abundant crustacean zooplankton prey resources (Yurista & Schulz 1995). Intense fish planktivory has also been proposed to explain establishment failure across the range of B. longimanus (MacIsaac et al. 2000, Branstrator et al. 2006). I examined whether the abiotic habitat and prey resources in Island Lake during summer were more suitable for B. longimanus than those of Fish Lake or Boulder Lake. Because no pre-invasion data were available, post-invasion conditions were monitored during the summer for 3 years, and results were interpreted as (1) factors contributing to invasion suc- cess and (2) ecological consequences of a persistent invasion in Island Lake.