ABsrrAcr we tested .otT*Tli:,'l; ?ffiT;lif#'#'i#Lr, barberi (coquiuett) on yo'r'g lawae of Aedes triseriotus (Say) redrrcei intraspecidc competition among suwiving prey and tbereby increases survival, mass at eclosion, and estimated rate of popubtln increase, or decreases development time for A. trismiatus. In a ffeld experiment manipulating both litter (=food)abundanceandpredatorabundance,totalsurvivorshipofA. taseriainwas\igniffcantly reduced by A. barbt; predation in tree holes, but not in iires where overall suivival was extremely low. Survival to adulthood and estimated ffnite rate of increase (1,') were signiffcantly Iower in low-food treatments, but were unaffected by the predator. Days to and mass at eclosion were unaffected by-predation. 'fhis ffeld experiment thus provided no evidence for a positive effect of predation by A. barberi-on A. triseriatus population performance. A laboratoi, furctional response experiment yielded no asymptotic saturationof number of prey killed by A. bar_beri of any instar. Fourth-instar A. barberi feeding on either lstor znd-in; bt A. triseriatw had indistinguishable functional responses, but 3rd-Gstar A. barbri killed signiffcantly fewer lst-instar prey than did 4th-instar A. barberi, and did not kill 2nd-instar prey. bensuses of tree holes and tires showed limited seasonal co-occurrence of predator-prey in-star combinations that can lead to predation. These data suggest that A. barsq;has only a limited potential to reduce populations of A. t?isriahrs and that such effects are likely only during a short period in midsummer.

We sampled three habitats (main channel, side channels, and backwater lakes) during 2 yr along 32 km of the Illinois River to compare zooplankton distribution and dynamics, as well as evaluate the possible effects of hydrology on taxonomic abundance and distribution. Zooplankton assemblages displayed both spatial and temporal variation. Whereas the riverine zooplankton assemblage was dominated by rotifers, the backwater lake assemblage was dominated by copepods. Zooplankton densities in the main channel peaked earlier in the season in both years than the backwater lake habitats. To determine if these patterns were caused by fluvial exchanges occurring between habitats during flooding, we sampled the connections between the backwater lake and main channel habitats and found that large numbers of zooplankton entered the main channel via these connections. Further, calculations of main channel population growth, birth, and death rates showed that population growth rates most commonly exceeded birth rates during the flooding period. Seasonal inoculums from off-channel habitats could play an important role in riverine zooplankton dynamics. However, for the main channel to achieve the measured zooplankton densities, ,400,000 backwater lakes would be required and zooplankton would need to travel an unrealistic number of days and distance based on estimated growth rates. Thus, other mechanisms (hatching of resting eggs or in situ reproduction) are likely responsible for zooplankton abundances.

Several traits related to foraging behaviour were assessed in young-of-the-year produced from largemouth bass Micropterus salmoides that had been exposed to four generations of artificial selection for vulnerability to angling. As recreational angling may target foraging ability, this study tested the hypothesis that selection for vulnerability to angling would affect behaviours associated with foraging ecology and prey capture success. Fish selected for low vulnerability to angling captured more prey and attempted more captures than high vulnerability fish. The higher capture attempts, however, ultimately resulted in a lower capture success for low vulnerability fish. Low vulnerability fish also had higher prey rejection rates, marginally shorter reactive distance and were more efficient at converting prey consumed into growth than their high vulnerability counterparts. Selection due to recreational fishing has the potential to affect many aspects of the foraging ecology of the targeted population and highlights the importance of understanding evolutionary effects and how these need to be considered when managing populations.

Early life stages of fishes are sensitive to ecological and environmental disturbances and experience very high mortality rates. During early ontogeny, the growth and survival of larval fish often depends on food availability. Because habitat and diet shifts are strongly tied to individual body size, factors that influence the growth rates of individuals (e.g. resource limitation, competition) also affect other aspects of ontogeny including the timing of habitat or diet shifts. In the context of biological invasions, non‐native species can potentially disrupt the interaction of larval fish with their food via competition for shared prey, reducing growth and survival during a vulnerable period of an organism's life history. We hypothesised that invasive planktivores negatively affect native species through the vulnerable larval life stage via competition for zooplankton resources. To test this hypothesis, we conducted a series of experiments to assess and contrast the effects of invasive (bighead carp, Hypophthalmichthys nobilis) and native (golden shiners, Notemigonus crysoleucas) planktivores on zooplankton densities, and their effects on the growth, survival, abundance, and habitat use of larval bluegill (Lepomis macrochirus). Overall, the effects of the invasive planktivore were consistently greater than the native planktivore in terms of reduced prey densities, reduced bluegill growth rates, and delays to the timing of ontogenetic habitat shifts. Growth rates of bluegill larvae were reduced by 58–87% in the presence of bighead carp and 37% in the presence of golden shiners (relative to controls), but such reductions did not consistently lead to reduced survival (in mesocosm experiment) or relative abundance (in pond experiment). However, we estimated that bighead carp and golden shiners delayed ontogenetic habitat shifts in bluegill by 9–24 and 1–3 days, respectively. Although we did not detect an effect of planktivores on the numbers of larval bluegill, our findings suggest that bighead carp may still affect bluegill ontogeny and freshwater food webs by disrupting the timing of ontogenetic habitat shifts. By affecting the coupling of habitats via organism movements during early ontogeny, bighead carp may indirectly disrupt predator–prey interactions of native taxa.

-Antipredator defences in prey species are moulded largely by predation. One general expectation is that an organism's size, shape or morphology determines the optimal set of corresponding behavioural antipredator responses. We test the hypothesis that species with similar morphology and ecology exhibit similar antipredator responses by quantifying and comparing avoidance and escape responses of two similar species, leatherside chub and redside shiner. We also examine how antipredator responses of these two species translate into mortality using experimental stream enclosures. In the presence of brown trout, redside shiner increased activity level, responded to a simulated attack sooner, quicker and had a more manoeuvrable escape than leatherside chub. Predation by brown trout decreased survival of both species, but caused higher levels of mortality in leatherside chub compared with redside shiner. Similar morphology and ecology of these two prey species does not correspond to similarity in avoidance and escape responses, and this difference has consequences for the long-term survival of these species in the presence of introduced brown trout.