Abstract. Predicting establishment of exotic species is a central goal of invasion biology, and is dependent upon propagule pressure and population processes. We introduced invading spiny water fleas, Bythotrephes longimanus at different propagule pressures into 19 experimental enclosures, following populations over asexual generations, resting egg production, and emergence in the following year. We integrated experimental results with field data to generate a stochastic population model, predicting establishment in relation to propagule pressure and introduction date. Our results suggested that Allee effects are operational at higher densities or smaller volumes than previously predicted, that stochasticity plays an important role in establishment, and demographic stochasticity may be correlated between individuals. Further, our novel theoretical derivations suggest that organisms should modify their sex ratios to reduce Allee effects. The functional form using adaptive sex-ratios was consistent with both mesocosm and field data. Despite the occurrence of Allee effects and stochasticity, there was still no date during the growing season where we predict lakes to be entirely safe from Bythotrephes invasions. A single propagule had approximately a 0.15 establishment probability in our mesocosms, if introduced early in the season; propagule pressures of 10 had . 0.50 probability, regardless of introduction date.Key words: adaptation; Allee effects; exotic species; mesocosm experiment; non-indigenous species; optimality; population dynamics; probability; sex-ratio.

Real-world uncertainties and data limitations make it difficult to predict how, when and where non-indigenous species (NIS) will spread. Typically only a small fraction of sites are sampled during only a few time intervals, such that we know neither the full spatial extent nor the true temporal progress of invasion. Yet, these unsampled locations might affect the invasion dynamics. We extend propagule pressure models to incorporate both human-mediated and natural fluvial dispersal vectors, and develop techniques to incorporate missing spatial and temporal data on invasions. We apply our model to Bythotrephes longimanus, a high-risk aquatic NIS, using a regional-scale 311-lake survey in a popular watershed in Ontario and extending our analysis to 1,300 unsampled lakes. Of 100 model runs with different random subsets of 50 sampled lakes reserved for validation, we were able to obtain an average area under the curve value of 0.89. Human-mediated dispersal accounted for 99.75% of the contribution of propagules to probability of establishment. Although the discovery rate is accelerating, our results suggest the annual rate of lake invasions is decelerating over time. Management efforts controlling recreational boating traffic out of the largest lakes in the system will be the most effective way of slowing the spread of B. longimanus in lakes within this system.

No abstract

Lake Ontario water levels are regulated under the International Joint Commission's Order of Approval. We assessed the availability of spawning habitat for eight fish guilds (grouped by vegetation and spawning temperature preferences) that use nearshore habitat in the Bay of Quinte, Lake Ontario, under regulated and pre-project water level scenarios. Our model used habitat characteristics of depth, substrate, vegetation cover and temperature across 14,876 habitat units and guild-based habitat suitabilities to assess the weighted suitable area (WSA) available for spawning. During the modelled 1951–2000 period, regulated water levels were on average 0.25 m lower than pre-project levels and varied about half as much. Overall, the large and shallow upper bay within the Bay of Quinte benefited from pre-project flows whereas the smaller and deeper lower bay benefited from regulated flows. Higher variance in water levels increased highly suitable wetland area and higher mean water levels increased the availability of shallow flooded area in the upper and middle bays, where the bathymetry is gradually sloping. The number of days over which WSA was available was generally greater for high temperature guilds, and appeared to decrease when temperature mismatches occurred in a season. Results emphasize the complexity of the relationship between fish habitat supply and water level regime.