Sediment impacts on sponges and a deep-sea coral in New Zealand

<p><b>Increased levels of suspended sediment in the water column are important factors contributing to the degradation of marine ecosystems worldwide. In coastal waters, temporal variation in suspended sediment concentrations (SSCs) occurs naturally due to seasonal and oceanographic processes. However, there is evidence that anthropogenic activities are increasing sediment concentrations. The volume of sediment moving from land-based sources into coastal ecosystems and human activities in the ocean disturbing the seafloor, such as dredging and bottom-contact fisheries, have been increasing over the last century. In addition, offshore activities, particularly bottom-contact fishing and potential deep-sea mining, can create sediment plumes in the deep-sea that may extend over long distances. Elevated suspended sediment concentrations have detrimental effects on benthic communities, particularly for suspension feeders like sponges and corals.</b></p> <p>The aim of this thesis was to investigate the effects of increased SSCs that might arise from heavy anthropogenic disturbance on common shallow water and deep-sea sponges and a deep-sea coral in New Zealand, as these groups contribute to habitat structure in some benthic environments, including the deep sea.</p>

Sediment impacts on sponges and a deep-sea coral in New Zealand

<p><b>Increased levels of suspended sediment in the water column are important factors contributing to the degradation of marine ecosystems worldwide. In coastal waters, temporal variation in suspended sediment concentrations (SSCs) occurs naturally due to seasonal and oceanographic processes. However, there is evidence that anthropogenic activities are increasing sediment concentrations. The volume of sediment moving from land-based sources into coastal ecosystems and human activities in the ocean disturbing the seafloor, such as dredging and bottom-contact fisheries, have been increasing over the last century. In addition, offshore activities, particularly bottom-contact fishing and potential deep-sea mining, can create sediment plumes in the deep-sea that may extend over long distances. Elevated suspended sediment concentrations have detrimental effects on benthic communities, particularly for suspension feeders like sponges and corals.</b></p> <p>The aim of this thesis was to investigate the effects of increased SSCs that might arise from heavy anthropogenic disturbance on common shallow water and deep-sea sponges and a deep-sea coral in New Zealand, as these groups contribute to habitat structure in some benthic environments, including the deep sea.</p>

Altered fire regimes modify lizard communities in globally endangered Araucaria forests of the southern Andes

Wildfire regimes are being altered in ecosystems worldwide. The density of reptiles responds to fires and changes to habitat structure. Some of the most vulnerable ecosystems to human-increased fire frequency are old-growth Araucaria araucana forests of the southern Andes. We investigated the effects of wildfires on the density and richness of a lizard community in these ecosystems, considering fire frequency and elapsed time since last fire. During the 2018/2019 southern summer season, we conducted 71 distance sampling transects to detect lizards in Araucaria forests of Chile in four fire “treatments”: (1) unburned control, (2) long-term recovery, (3) short-term recovery, and (4) burned twice. We detected 713 lizards from 7 species. We found that the density and richness of lizards are impacted by wildfire frequency and time of recovery, mediated by the modification of habitat structure. The lizard community varied from a dominant arboreal species (L. pictus) in unburned and long-recovered stands, to a combination of ground-dwelling species (L. lemniscatus and L. araucaniensis) in areas affected by two fires. Araucaria forests provided key habitat features to forest reptiles after fires, but the persistence of these old-growth forests and associated biodiversity may be threatened given the increase in fire frequency.

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>

A vegetation classification and description of white-winged flufftail ( Sarothrura ayresi ) habitat at selected high-altitude peatlands in South Africa

The white-winged flufftail is listed as critically endangered, and limited knowledge about the species' ecology has been identified as a limiting factor to effectively conserving the bird. Little is known about the vegetation inhabited by the white-winged flufftail, which hampers the identification and management of its habitat. This study presents a fine-scale classification and description of the vegetation of wetland sites where the bird is known to be present. A plant phytosociological study was conducted to describe the plant communities and vegetation structure of the habitat. Three sites were selected at Verloren Valei Nature Reserve and two at Middelpunt Wetland, Mpumalanga, South Africa, shortly after the white-winged flufftail breeding season. A total of 60 sample plots were placed within the study sites, where all plant species present were recorded and identified. Other aspects such as plant height, water depth and anthropogenic influences were also documented. A modified TWINSPAN analysis resulted in the identification of three sub-communities that can be grouped into one major community. The Cyperaceae, Asteraceae and Poaceae families dominate the vegetation, with the sedges Carex austro-africana and Cyperus denudatus being dominant, and the grasses Leersia hexandra and Arundinella nepalensis co-dominant. The broad habitat structure consisted of medium to tall herbaceous plants (0.5–0.7 m) with shallow slow-flowing water.