No description available.

Thesis (M.S.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 110-119). Also available on the World Wide Web.

The white perch (Morone americana) is a highly successful invader of freshwater systems, with negative consequences to some resident fishes. White perch are ovivores and may prey upon as well as compete with juvenile sportfishes. Since 1988, an introduced population of white perch has proliferated in the 19,790-ha Kerr Reservoir, NC-VA, potentially threatening popular sport fisheries for largemouth bass (Micropterus salmoides), crappie (Pomoxis spp.), and self-sustaining striped bass (Morone saxatilis). Trophic relationships between white perch and resident sportfish were examined in the Kerr Reservoir system to determine the white perch's impact on them. Striped bass eggs were found in the stomach contents of white perch collected from the Roanoke River during their concurrent spawning runs in May, and at times egg predation was intense (frequency of egg occurrence in white perch individuals up to 100 %). However, modeling simulations indicated that observed densities of white perch in the Roanoke River during the peak spawning period of striped bass (May) were too low to have a substantial effect on striped bass recruitment. Crappie eggs were found in the diets of white perch collected from Kerr Reservoir during April, but the significance of this predation was not determined. Trophic overlap (Schoener's Index) was high (> 0.5) between age-0 white perch and age-0 crappie, largemouth bass, and striped bass in June, but only remained high between white perch and crappie in the remainder of the growing season (July – September). After June, largemouth and striped bass were primarily piscivorous, whereas white perch and crappie remained primarily invertivorous. Trophic overlap was high between adult white perch and adult crappie (> 0.6), but not between white perch and any other species of adult sportfish. The utilization of white perch by adult piscivores (Ictalurids, Pomoxis spp., Moronids, and Percids) as a food source was low (< 2% of diets by weight). Piscivorous sportfish primarily ate clupeids, which are highly abundant in Kerr Reservoir. Analysis of sportfish performance before (1974 – 1987) versus after (1996 – 2005) white perch establishment indicated no change in abundance and growth of striped bass and largemouth bass. Performance data for crappie prior to white perch introductions were unavailable, but observed egg predation by and trophic overlap with white perch suggests that crappie have the highest potential to suffer deleterious interactions with the white perch. Abundance of white bass has significantly declined in years since white perch introductions. Future research in Kerr Reservoir should concentrate on interactions between white perch and these two species. / Master of Science

<p>Recent studies show that populations of the freshwater isopod <em>Asellus aquaticus L. can rapidly become locally differentiated when submerged stonewort (<em>Chara spp.) vegetation expands in lakes. In the novel <em>Chara habitat, isopods become lighter pigmented and smaller than in the ancestral reed stands. In this study, I used laboratory experiments to investigate if selective predation by fish could be a possible explanation for these phenotypic changes. Predation from fish is generally considered to be a strong selective force on macroinvertebrate traits. In the first experiment I measured perch (<em>Perca fluviatilis L.) handling time for three size classes of <em>Asellus to see which size of those that would be the most profitable to feed upon. No difference in handling time was detected between prey sizes, hence the largest size would be the most beneficial to feed upon. In a second experiment I let perch feed on a mixture of <em>Asellus phenotypes in aquaria manipulated to mimic the substrates in either the <em>Chara or the reed habitats. Remaining isopods were significantly smaller and lighter pigmented in the fish aquaria than in the controls, showing that the perch preferred to feed on large and dark individuals. In the <em>Chara habitat, selection on isopod pigmentation was according to what could be expected from background matching, but in the reed habitat selection was quite the opposite. These results support the hypothesis that predation from fish is a strong selective force behind the rapid local adaptation seen in <em>Asellus populations in the novel <em>Chara habitat. </em></em></em></em></em></em></em></em></em></em></p>

Recent studies show that populations of the freshwater isopod Asellus aquaticus L. can rapidly become locally differentiated when submerged stonewort (Chara spp.) vegetation expands in lakes. In the novel Chara habitat, isopods become lighter pigmented and smaller than in the ancestral reed stands. In this study, I used laboratory experiments to investigate if selective predation by fish could be a possible explanation for these phenotypic changes. Predation from fish is generally considered to be a strong selective force on macroinvertebrate traits. In the first experiment I measured perch (Perca fluviatilis L.) handling time for three size classes of Asellus to see which size of those that would be the most profitable to feed upon. No difference in handling time was detected between prey sizes, hence the largest size would be the most beneficial to feed upon. In a second experiment I let perch feed on a mixture of Asellus phenotypes in aquaria manipulated to mimic the substrates in either the Chara or the reed habitats. Remaining isopods were significantly smaller and lighter pigmented in the fish aquaria than in the controls, showing that the perch preferred to feed on large and dark individuals. In the Chara habitat, selection on isopod pigmentation was according to what could be expected from background matching, but in the reed habitat selection was quite the opposite. These results support the hypothesis that predation from fish is a strong selective force behind the rapid local adaptation seen in Asellus populations in the novel Chara habitat.

A mesocosm experiment was conducted in Lake Eymir between June &ndash / September 2009 in order to elucidate the effects of water level changes and fish predation on periphyton growth and macroinvertebrates in semi-arid shallow lakes. Twenty four cylindrical enclosures, each with 1.2 m diameter, open to lake bottom and atmosphere, were placed at three different depths, i.e. 0.8 m (low water level, LW), 1.6 m (high water level, HW) and 2.3 m (however, data regarding the enclosures at 2.3 m were excluded in this study due to complications after fifth sampling) to simulate water level fluctuations. At each water level, four replicates were stocked with omnivorous&ndash / planktivorous fish (Tinca tinca and Alburnus escherichii) and the other four replicates were left fishless to observe the effect of fish predation. Ten shoots of submerged macrophytes (Potamogeton pectinatus) were planted and six polyethylene strips were hung in the water column in each enclosure to monitor macrophyte and periphyton growth. The mesocosms were sampled for physical, chemical and biological parameters weekly in the first month and fortnightly thereafter. Benthic macroinvertebrate samples were taken before the start, in the middle and at the end of the experiment with Kajak corer. Macrophytes were harvested after the last sampling for determination of dry weight, epiphyton, and the associated macroinvertebrates. All macroinvertebrate samples were sieved through 212 &mu / m mesh size before identification and counting. Over the course of the experiment, an average of 0.46 &plusmn / 0.03 m water level decrease in the mesocosms triggered submerged macrophyte growth in all LW enclosures, overriding the negative effects of fish predation. The results indicate that while fish predation pressure had negative influences on macroinvertebrate communities in terms of both abundance and richness, structural complexity created by dense vegetation in the LW mesocosms weakened the top-down effect of fish on macroinvertebrates by acting as a refuge in this semi-arid shallow lake.

No description available.

I investigated the value of under-road tunnels as a conservation strategy to protect a long-toed salamander population, in south-west Alberta, whose overwintering sites and breeding habitat (Linnet Lake) are separated by a road. I conducted a mark-recapture study from 2008-2009, capturing salamanders using roadside fences and pitfall traps. Four tunnels were monitored in 2009 using traps and cameras. A 2008 estimate indicated that the population declined by 60% since 1994, however, road mortality was dramatically reduced following installation of fences and tunnels. Camera and trap data documented 130 salamanders navigating tunnels in 2009. I found little evidence of juvenile recruitment from Linnet Lake, likely because of predation by lake chub. Experiments showed that lake chub consumed salamander larvae, and fish presence altered larval behaviour. Continued monitoring is needed to determine if reduced road mortality translates into population gains, and whether fish predation threatens the persistence of the long-toed salamander population. / Ecology

The impact of fish predation on zooplankton assemblage was studied in the mesocosm experiment. Presented thesis focuses on the effect of size selective fish predation on species diversity, biomass and body sizes of zooplankton and the impact of fish occurrence on zooplankton behaviour with regard to diel horizontal migration. I also studied a change in some life history traits of zooplankton caused by fish with a special focus on keystone species of freshwater ecosystems Daphnia spp.

The prey consumption by benthivorous fish predators can have profound top-down effects in stream food webs. To analyse this effects in small temperate stream ecosystems, a long-term field experiment was conducted in two streams in South-eastern Germany, Gauernitzbach and Tännichtgrundbach, from 2004 to 2011. The densities of two small-bodied benthivorous fish species, gudgeon (Gobio gobio) and stone loach (Barbatula barbatula), were manipulated following a Before-After-Control-Impact design. The top predator regime affected the benthic community composition of the streams mainly in pools, whereas the total benthic invertebrate biomass was not affected in any mesohabitat. The present work describes a causal analysis of the observed food web effects using additional field analyses and laboratory experiments, with a special focus on the habitat use and foraging behaviour of the fish as top predators. The probably most important of the analysed mechanisms was mesohabitat-specific predation by the fish. Three 24-h field video surveys combined with benthic invertebrate sampling showed that constraints in habitat use, especially for gudgeon, induced a differential predator-prey habitat overlap which resulted in a higher predation risk for the invertebrate prey in pools than in riffles. Another important mechanism was selective predation of both fish species. Their prey selectivity was largely explained by a small number of prey variables being connected to the partly non-visual foraging mode of these benthic predators. Besides the traits body size and feeding type, long-term mean abundance played a central role, small and highly abundant invertebrates, grazers and sediment feeders being preferred by gudgeon and stone loach. The preference for small and abundant prey taxa (chironomids) exceeded purely opportunistic feeding and probably facilitated resource partitioning between the two fish species having very similar diets. In addition to active selectivity, different predator avoidance strategies of the invertebrates analysed in laboratory experiments explained the passive selectivity of the fish predators for certain prey taxa in the streams. This could be shown for two abundant taxa being consumed by the fish predators in very different quantities, Gammarus pulex and Hydropsyche instabilis. These three mechanisms, although probably interacting with several other factors, could explain a large part of the effects the top-down food web manipulation had on the benthic community, especially the observed high degree of mesohabitat and species specificity. Confirming this, quantitative characteristics of predation food webs, for instance the importance of intraguild predation, differed markedly between pool and riffle mesohabitats. From the results of this study it can be concluded that the benthivorous fish affected benthic community structure mainly by mesohabitat-specific and selective predation. A manipulation of this (native) top predator type therefore will probably have such rather subtle but not catastrophic consequences in ecosystems with a high biotic diversity and a rich natural habitat structure and connectivity.