Relationship of Sphaeroma Quoianum to Sediment Characteristics and Invertebrate Community

Many important wetland functions are tied to sediment dynamics, which are largely governed by infaunal invertebrate communities. These communities are sensitive to changes in sediment structure and to colonization by non-native species. In a southern California salt marsh, the non-native Australian isopod Sphaeroma quoianum has created dense networks of burrows within the marsh banks. Since this isopod increases erosion in many areas and can change local invertebrate communities, its possible contribution to habitat loss in this already-scarce southern California ecosystem is an important question. This study connected S. quoianum burrows to increased proportions of crustaceans, decreased carbon content, and steep marsh bluffs. These results highlight the potential susceptibility of salt marsh habitat with steep edges to invasion by non-native species and demonstrate that such invasion can correlate to key changes in ecosystem function. These results also suggest that S. quoianum invasion of salt marsh habitats can alter native communities and ecosystem functions, thus incipient invasions should be of concern to managers and ecologists alike.

Salinity Affects Freshwater Invertebrate Traits and Litter Decomposition

We evaluated the effect of seawater intrusion in coastal ecosystems on the freshwater invertebrate community and on leaf litter decomposition under realistic scenarios in six outdoor freshwater mesocosms containing fauna and flora, to which increasing volumes of seawater were added. The resulting salinity values were 0.28 (control, freshwater only), 2.0, 3.3, 5.5, 9.3, and 15.3 mS cm−1. The effect of salinity was assessed for 65 days after seawater intrusion, by computing the deviation of values in each treatment in relation to the control. Our results show that seawater intrusion into freshwaters will affect the invertebrate communities and organic matter decomposition, with salinities of up to 3.3–5.5 mS cm−1 having opposite effects to salinities of more than 9.3 mS cm−1. There was a net negative effect of the two highest salinities on mass loss and richness of the invertebrates associated with the decomposing leaves. Regarding the invertebrate communities of the mesocosms, there was a net negative effect of the intermediate salinity levels on abundance and richness. Invertebrate life cycle traits conferring resilience and resistance tended to increase with low and decrease with high salinity values, while avoidance traits showed an opposite trend, and these responses were more pronounced on the later stage community. These wave-like responses of the invertebrate species traits to increasing salinity suggest that the life-history and physiological adaptations most suitable to cope with osmotic stress will differ between low and high salinity levels.

Habitat Structure, Resources and Natural Enemies: Their Influence on Population Fluctuations of the Kowhai Moth Uresiphita Polygonalis Maorialis (Felder)

<p><b>The importance of habitat structure has been historically discussed in terms of its influence on diversity, distribution and abundance of living organisms. In this regard, the population fluctuations of any particular species, particularly outbreaking insect species, can be expected to be profoundly influenced by the structure of the habitat. A set of ecological hypotheses, such as, the associational resistance, plant decoy, habitat heterogeneity and resource concentration have implicitly included the structure of the habitat determined by the structure (size, density, physical location) of the host plant and other surrounding plant species. Moreover, type, quality and availability of resources, in addition to the presence of other interacting organisms, e.g. competitors, predators and parasites, have also been considered determining factors in the population fluctuation of outbreaking species. The aim of this thesis is to contribute to the understanding of how the outbreaks of the kowhai moth, U. polygonalis maorialis, relate to the physical structure of the habitat, the availability of resources, specific host plants and to natural enemies.</b></p> <p>In the first experimental chapter of my thesis I studied the fluctuations of the U. polygonalis maorialis larvae and their impacts on the defoliation levels of Sophora spp. plants. I carried out a survey in urban and suburban areas of Wellington city. I examined levels of defoliation of the host plants and population fluctuations in terms of a set of biotic and abiotic variables. These variables were selected in order to cover a range of measures of habitat structure, resource availability and invertebrate community. I modelled such responses to find which variables better explained the observed defoliation and larval population fluctuations. The best fitted model showed that levels of observed defoliation were explained by the structure of the vegetation surrounding the main host plant (vertical and horizontal) and the species of host plant. Population fluctuations of the kowhai moth were explained by the following predicting variables: density of natural enemies, structure of the vegetation surrounding the main host plant (vertical and horizontal), host plant size, level of habitat disturbance, type of habitat (urban/suburban) and the Sophora spp.</p> <p>In my second experimental chapter, I focused on the importance of availability of resources to explain observed densities of U. polygonalis maorialis and phytophagous insects. In my observational experiment I tested the resource concentration hypothesis and the natural enemies hypothesis, by studying the fluctuations of U. polygonalis maorialis larvae on individuals of Sophora microphylla plants located in gardens across Wellington city. Larval densities were found to be higher on smaller plants than large plants, whereas natural enemies did not show specific responses to plant size. In my manipulative experiment I originally aimed for the establishment of U. polygonalis maorialis in the experimental plots. Unfortunately, these were not colonised by U. polygonalis maorialis, instead I studied phytophagous insects that colonised the plots. I found no differences among the S. microphylla treatments for the levels of establishment of phytophagous invertebrates. On the contrary, the amount of nil records was high and there was an overall high variability among treatments and low rate of establishment throughout the sampling season. Nevertheless, natural enemies were found to occur more often at higher densities in plots with lower plant density in only two specific dates.</p> <p>Uresiphita polygonalis maorialis is the main defoliator of Sophora spp in New Zealand. In this context I studied the feeding and oviposition preferences of the moth for the three most commonly found species of Sophora plants in Wellington city. Sophora tetraptera was the preferred species chosen by the female moth. The same species was also the most palatable and preferred when confronted to S. microphylla and S. prostrata. These patterns observed in controlled conditions are coincident with observations made in the field throughout the study.</p> <p>Within the set of variables determined by the invertebrate community, the influence of natural enemies on an herbivorous population is one of the most important in terms of population regulation. In my last experimental chapter I found a positive correlation among the parasitism by M. pulchricornis and U. polygonalis maorialis larval densities, which opens the possibilities for future research to explore the potential existence of population regulation mechanisms between these two taxa.</p> <p>Overall, the results of my thesis highlight the importance of understanding the influence of the structure of the habitat, types of resources provided by plants and natural enemies in determining the fluctuations of outbreaking insect species.</p>

Habitat Structure, Resources and Natural Enemies: Their Influence on Population Fluctuations of the Kowhai Moth Uresiphita Polygonalis Maorialis (Felder)

<p><b>The importance of habitat structure has been historically discussed in terms of its influence on diversity, distribution and abundance of living organisms. In this regard, the population fluctuations of any particular species, particularly outbreaking insect species, can be expected to be profoundly influenced by the structure of the habitat. A set of ecological hypotheses, such as, the associational resistance, plant decoy, habitat heterogeneity and resource concentration have implicitly included the structure of the habitat determined by the structure (size, density, physical location) of the host plant and other surrounding plant species. Moreover, type, quality and availability of resources, in addition to the presence of other interacting organisms, e.g. competitors, predators and parasites, have also been considered determining factors in the population fluctuation of outbreaking species. The aim of this thesis is to contribute to the understanding of how the outbreaks of the kowhai moth, U. polygonalis maorialis, relate to the physical structure of the habitat, the availability of resources, specific host plants and to natural enemies.</b></p> <p>In the first experimental chapter of my thesis I studied the fluctuations of the U. polygonalis maorialis larvae and their impacts on the defoliation levels of Sophora spp. plants. I carried out a survey in urban and suburban areas of Wellington city. I examined levels of defoliation of the host plants and population fluctuations in terms of a set of biotic and abiotic variables. These variables were selected in order to cover a range of measures of habitat structure, resource availability and invertebrate community. I modelled such responses to find which variables better explained the observed defoliation and larval population fluctuations. The best fitted model showed that levels of observed defoliation were explained by the structure of the vegetation surrounding the main host plant (vertical and horizontal) and the species of host plant. Population fluctuations of the kowhai moth were explained by the following predicting variables: density of natural enemies, structure of the vegetation surrounding the main host plant (vertical and horizontal), host plant size, level of habitat disturbance, type of habitat (urban/suburban) and the Sophora spp.</p> <p>In my second experimental chapter, I focused on the importance of availability of resources to explain observed densities of U. polygonalis maorialis and phytophagous insects. In my observational experiment I tested the resource concentration hypothesis and the natural enemies hypothesis, by studying the fluctuations of U. polygonalis maorialis larvae on individuals of Sophora microphylla plants located in gardens across Wellington city. Larval densities were found to be higher on smaller plants than large plants, whereas natural enemies did not show specific responses to plant size. In my manipulative experiment I originally aimed for the establishment of U. polygonalis maorialis in the experimental plots. Unfortunately, these were not colonised by U. polygonalis maorialis, instead I studied phytophagous insects that colonised the plots. I found no differences among the S. microphylla treatments for the levels of establishment of phytophagous invertebrates. On the contrary, the amount of nil records was high and there was an overall high variability among treatments and low rate of establishment throughout the sampling season. Nevertheless, natural enemies were found to occur more often at higher densities in plots with lower plant density in only two specific dates.</p> <p>Uresiphita polygonalis maorialis is the main defoliator of Sophora spp in New Zealand. In this context I studied the feeding and oviposition preferences of the moth for the three most commonly found species of Sophora plants in Wellington city. Sophora tetraptera was the preferred species chosen by the female moth. The same species was also the most palatable and preferred when confronted to S. microphylla and S. prostrata. These patterns observed in controlled conditions are coincident with observations made in the field throughout the study.</p> <p>Within the set of variables determined by the invertebrate community, the influence of natural enemies on an herbivorous population is one of the most important in terms of population regulation. In my last experimental chapter I found a positive correlation among the parasitism by M. pulchricornis and U. polygonalis maorialis larval densities, which opens the possibilities for future research to explore the potential existence of population regulation mechanisms between these two taxa.</p> <p>Overall, the results of my thesis highlight the importance of understanding the influence of the structure of the habitat, types of resources provided by plants and natural enemies in determining the fluctuations of outbreaking insect species.</p>

Factors Promoting Coexistence between Endemic Ants and Invasive Wasps

<p>Invasive animals can alter the community composition of native ecosystems by means of competition and predation. In this study I investigated the factors that may facilitate coexistence between endemic ants and invasive wasps. Previous research has shown that entire communities can be impacted by invasions. Endemic species subject to pressure from invasive species may undergo a niche shift to enable coexistence and minimise the impact of this pressure. The invertebrate community composition of Nothofagus forests in the South Island of New Zealand has been altered by predation from Invasive Vespula wasps. Ants and wasps in this ecosystem coexist on the same trophic level; they simultaneously fill multiple trophic roles as primary predators, secondary predators, and primary consumers. The outcome of competition between species such as ants and wasps is not easy to predict, and may vary in different communities and with different densities of competitors. In this dissertation I aimed to determine the extent to which competition occurs between native ants and invasive Vespula wasps, and to investigate the impacts of invasion on the native invertebrate community. I quantified the invertebrate community composition of Nothofagus forests and then experimentally reduced wasp numbers to investigate any changes as a result of a reduction in predation or competition. The observed changes in community composition were as a result of differing abundances of taxonomic groups within my study sites. In order to more robustly determine the community effects of wasp removal it may be necessary to reduce wasp numbers by up to 90% for many years. Even under these conditions, species that are particularly vulnerable to wasp predation or competition may have already been permanently excluded from this system. I then investigated temporal niche shifts by native ants when faced with reduced competition for food resources from invasive wasps. There was an increase in the numbers of ants foraging on honeydew when I experimentally reduced wasp numbers. This increase may be due to increases in both the quantity and quality of the available honeydew. When densities of wasps were substantially reduced there was a difference in the foraging abundances of ants and wasps; however, there was no change in the overall temporal foraging pattern of ants. Isotope ratios and consequently trophic levels of native competitors may change in response to the removal of an invasive species. To test this I examined changes in isotope ratios as a result of removal of wasps. The observed changes in the trophic levels of both ants and wasps appear to be a result of natural seasonal variation in consumption related to the nutritional requirements of the colony. Finally, I examined behavioral interactions between native ants and invasive wasps during foraging. This study has indicated that wasps may find and access resources more readily when ants are present. Native ants may facilitate foraging by wasps, as demonstrated by the increase in wasp numbers when foraging in the presence of ants. Additionally, the impact of competition between wasps and ants is likely to be density dependant. Co-occurrence between endemic and invasive competitors is possible through two important mechanisms, niche separation and behavioural adaptations. Native ants in this system are able to forage in different temporal niches than invasive wasps, and their dominant behaviour serves to diminish competitive interactions. These findings have implications for the ecology of these forests in understanding the considerable impact that invasive species may have on native ecosystems and particularly those species which have similar resource requirements.</p>

Factors Promoting Coexistence between Endemic Ants and Invasive Wasps

<p>Invasive animals can alter the community composition of native ecosystems by means of competition and predation. In this study I investigated the factors that may facilitate coexistence between endemic ants and invasive wasps. Previous research has shown that entire communities can be impacted by invasions. Endemic species subject to pressure from invasive species may undergo a niche shift to enable coexistence and minimise the impact of this pressure. The invertebrate community composition of Nothofagus forests in the South Island of New Zealand has been altered by predation from Invasive Vespula wasps. Ants and wasps in this ecosystem coexist on the same trophic level; they simultaneously fill multiple trophic roles as primary predators, secondary predators, and primary consumers. The outcome of competition between species such as ants and wasps is not easy to predict, and may vary in different communities and with different densities of competitors. In this dissertation I aimed to determine the extent to which competition occurs between native ants and invasive Vespula wasps, and to investigate the impacts of invasion on the native invertebrate community. I quantified the invertebrate community composition of Nothofagus forests and then experimentally reduced wasp numbers to investigate any changes as a result of a reduction in predation or competition. The observed changes in community composition were as a result of differing abundances of taxonomic groups within my study sites. In order to more robustly determine the community effects of wasp removal it may be necessary to reduce wasp numbers by up to 90% for many years. Even under these conditions, species that are particularly vulnerable to wasp predation or competition may have already been permanently excluded from this system. I then investigated temporal niche shifts by native ants when faced with reduced competition for food resources from invasive wasps. There was an increase in the numbers of ants foraging on honeydew when I experimentally reduced wasp numbers. This increase may be due to increases in both the quantity and quality of the available honeydew. When densities of wasps were substantially reduced there was a difference in the foraging abundances of ants and wasps; however, there was no change in the overall temporal foraging pattern of ants. Isotope ratios and consequently trophic levels of native competitors may change in response to the removal of an invasive species. To test this I examined changes in isotope ratios as a result of removal of wasps. The observed changes in the trophic levels of both ants and wasps appear to be a result of natural seasonal variation in consumption related to the nutritional requirements of the colony. Finally, I examined behavioral interactions between native ants and invasive wasps during foraging. This study has indicated that wasps may find and access resources more readily when ants are present. Native ants may facilitate foraging by wasps, as demonstrated by the increase in wasp numbers when foraging in the presence of ants. Additionally, the impact of competition between wasps and ants is likely to be density dependant. Co-occurrence between endemic and invasive competitors is possible through two important mechanisms, niche separation and behavioural adaptations. Native ants in this system are able to forage in different temporal niches than invasive wasps, and their dominant behaviour serves to diminish competitive interactions. These findings have implications for the ecology of these forests in understanding the considerable impact that invasive species may have on native ecosystems and particularly those species which have similar resource requirements.</p>

Trocheta ariescornuta n. sp. (Annelida, Hirudinida: Erpobdellidae) – a new cavernicolous leech from Motena Cave in Georgia

A new leech species Trocheta ariescornuta n. sp. is described and illustrated here based on two specimens found in Motena Cave in western Georgia, Caucasus. This species differs from the known congeners and other similar Erpobdellids of the region, including Georgian cavernicolous leech - Dina ratschaensis Kobaķhidze, 1958 in a complex of external and internal morphological characteristics: colour, annulation, position of genital pores, shape of the genital atrium with strong coiled cornua (similar to the horns of a ram). Cave inhabitant invertebrate community for Motena Cave is provided.