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Caracterização genética de populações de jacaré-de-papo-amarelo (Caiman latirostris), utilizando marcadores microssatélites. / Genetic characterization of broad-snouted caiman (Caiman latirostris) populations by microsatellites markers.Villela, Priscilla Marqui Schmidt 18 May 2004 (has links)
Um componente considerado crítico para o manejo bem sucedido de populações silvestres é a manutenção da variação genética. No intuito de avaliar a magnitude e a distribuição da variabilidade genética existente em populações de Caiman latirostris, nove populações distribuídas ao longo do eixo latitudinal da distribuição da espécie no Brasil e uma população em cativeiro foram estudadas com auxílio de onze locos microssatélites. A diversidade gênica média (He=h) e a heterozigosidade média observada (Ho) apresentaram valores elevados, 0,628 e 0,567, respectivamente, denotando existência de elevada variabilidade genética para esta espécie nas regiões de estudo. A população paulista mesmo estando na zona intermediária de distribuição geográfica no Brasil não possui a maior variabilidade genética. O valor FST estimado foi 0,270 e o RST foi 0,342. Ambas as medidas de diferenciação entre as populações foram significativas (P<0,05). As altas estimativas de FST e RST sugerem a ausência ou fluxo gênico restrito entre essas populações, exceção feita entre as populações de Natal (RN) e João Pessoa (PB), onde não houve diferenciação significativa entre as populações, sugerindo assim que há fluxo gênico entre elas, fato confirmado pelo coeficiente de parentesco. Pôde-se concluir neste trabalho que a distância genética entre a população do litoral é afetada pela existência da Serra do Mar como barreira geográfica pelo fato desta população apresentar as maiores diferenciações genéticas e não se agrupar a nenhuma população pelo método de agrupamento UPGMA, mesmo estando próxima das populações paulista. A distância genética entre as populações parece não acompanhar a distância geográfica, em termos de gradiente latitudinal (r=0,206). Entretanto quando retiramos a população da Ilha do Cardoso esta correlação aumenta significativamente (r=0,540), indicando haver um certo padrão espacial da variabilidade genética entre as populações. O coeficiente médio de parentesco foi baixo entre e dentro das populações estudadas. Com estes resultados podemos começar a entender a dinâmica e estrutura social de populações de Caiman latirostris, e quanto mais se compreende sobre a biologia destes animais mais precisa serão decisões visando condições que permitam a existência continua da espécie. / A component considered critical for the managment well succeed of wild populations it is the maintenance of genetic variation. In the intention of evaluating the extend and the distribution of the existent genetic variability in populations of Caiman latirostris, nine populations distributed along the latitudinal axis of the distribution of the species in Brazil and a population in captivity they were studied with aid of eleven locos microsatellite. The genic mean diversity (He=h) and the observed mean heterozygosity (Ho) across all loci for all populations ranged from 0,628 and 0,567, respectively, denoting existence high genetic variability. The population from São Paulo being in the intermediate zone of geographical distribution in Brazil doesn't possess the largest genetic variability. The value dear FST was 0,270 and RST it was 0,342. Both differentiation measures among the populations were significant (P < 0,05). The higher estimates of FST and RST suggested a absence or low gene flow among those populations, exception done between the populations of Natal (RN) and João Pessoa (PB), where there was not significant differentiation among the populations, suggesting a gene flow pattern among them, fact confirmed by the related coefficient. It could be concluded in this work that the genetic distance among the population of the coast is affected by the existence of the Mountain of the Sea as geographical barrier for the fact of this population to present the largest genetic differentiations and not to group the any population for the grouping method UPGMA, same being close of the populations from São Paulo. The genetic distance among the populations seems not to accompany the geographical distance, in terms of latitudinal gradient (r=0,206). However when we removed the population of Cardoso's Island this correlation it increases significantly (r= 0,540), indicating there to be a certain space pattern of the genetic variability among the populations. The medium coefficient of related was low among and inside of the studied populations. With these results we can begin to understand the dynamics and it structures social of populations of Caiman latirostris.
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Development, evaluation, and application of spatio-temporal wading bird foraging models to guide everglades restorationUnknown Date (has links)
In south Florida, the Greater Everglades ecosystem supports sixteen species of
wading birds. Wading birds serve as important indicator species because they are highly
mobile, demonstrate flexible habitat selection, and respond quickly to changes in habitat
quality. Models that establish habitat relationships from distribution patterns of wading
birds can be used to predict changes in habitat quality that may result from restoration
and climate change. I developed spatio-temporal species distribution models for the
Great Egret, White Ibis, and Wood Stork over a decadal gradient of environmental
conditions to identify factors that link habitat availability to habitat use (i.e., habitat
selection), habitat use to species abundance, and species abundance (over multiple scales)
to nesting effort and success. Hydrological variables (depth, recession rate, days since
drydown, reversal, and hydroperiod) over multiple temporal scales and with existing
links to wading bird responses were used as proxies for landscape processes that influence prey availability (i.e., resources). In temporal foraging conditions (TFC)
models, species demonstrated conditional preferences for resources based on resource
levels at differing temporal scales. Wading bird abundance was highest when prey
production from optimal periods of wetland inundation was concentrated in shallow
depths. Similar responses were observed in spatial foraging conditions (SFC) models
predicting spatial occurrence over time, accounting for spatial autocorrelation. The TFC
index represents conditions within suitable depths that change daily and reflects patch
quality, whereas the SFC index spatially represents suitability of all cells and reflects
daily landscape patch abundance. I linked these indices to responses at the nest initiation
and nest provisioning breeding phases from 1993-2013. The timing of increases and
overall magnitude of resource pulses predicted by the TFC in March and April were
strongly linked to breeding responses by all species. Great Egret nesting effort and
success were higher with increases in conspecific attraction (i.e., clustering). Wood Stork
nesting effort was closely related to timing of concurrently high levels of patch quality
(regional scale) and abundance (400-m scale), indicating the importance of a multi-scaled
approach. The models helped identify positive and negative changes to multi-annual
resource pulses from hydrological restoration and climate change scenarios, respectively. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2014. / FAU Electronic Theses and Dissertations Collection
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Modeling Long-Term Changes, 1958-2011, In The Reproduction And Territory Dynamics Of Bald Eagles Of Florida Bay, Southern Coastal EvergladesUnknown Date (has links)
As top-level piscivores, Bald Eagles are a compelling subject for the study of
territory dynamics and are highly representative of the distinctive suite of avian species
that occupy Florida Bay. Despite successful recovery of Bald Eagles (Haliaeetus
leuocephalus) throughout the species range, the population breeding within Florida Bay
has not mirrored this trend. Beginning in the late 1980s, Florida Bay has suffered in its
capacity to support species diversity and abundance as a result of extreme changes in
hydrology related to altered flows of incoming freshwater. In fact, Bald Eagle territory
use in Florida Bay has declined by as much as 43% as year to year variation and
sensitivity to transitions between territory states have increased. Florida Bay’s
populations of other large, conspicuous fish-eating birds, including Ospreys, Great White
Herons, Roseate Spoonbills, and Reddish Egrets each exhibit a similar pattern of decline. The effects of environmental degradation throughout Florida Bay are magnified at higher
trophic levels. The negative trend in territory occupancy is most pronounced in southeast
Florida Bay whereas effects on territory occupancy in the northwest are minimal. The
presence of spatial patterns in territory occupancy, despite regionally available breeding
birds, suggests that individuals are evaluating differences in habitat quality for which
certain territories are no longer considered viable. Building on our current understanding
of the health of this population of Bald Eagles, we have successfully implemented
modeling approaches that identify key territory breeding decisions. Loss of early
breeding season activity (occupied and active territories) despite maintaining high
breeding success indicates that changes in territory dynamics are the result of a failure to
breed and not a reproductive failure. As such, future conservation actions should
promote early breeding season activity (decisions by breeding pairs to initiate nesting) in
areas of Florida Bay that were historically occupied but are now abandoned. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2017. / FAU Electronic Theses and Dissertations Collection
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Lotic macroinvertebrate distribution patterns in northeastern OregonGerth, William J. 12 March 2004 (has links)
This study was an investigation of lotic macroinvertebrate distribution in
northeastern Oregon at two different spatial and biological scales. Examination
of assemblages at a limited spatial scale revealed relationships with natural and
disturbance gradients and led to questions about distribution of a population at
broader spatial scales.
In a 16 kilometer section of the North Fork John Day River, I examined
the relationship of invertebrate assemblages to habitat and fine sediment
deposition. This river section was subjected to sediment inputs resulting from
several years of floodplain mine-tailing leveling, and erosion and tributary
channel scouring following a forest fire. Invertebrate assemblages differed
between habitat types. The proportion of sediment tolerant invertebrates,
especially oligochaete worms, increased with higher amounts of deposited fine
sediment, but total invertebrate abundance was not related to deposited
sediment. The response of sediment tolerant invertebrates appeared to reflect
cumulative impacts from multiple input points and downstream transport of
sediment and cumulative and/or increasing impacts over the two years of
sampling.
In studying assemblages in the North Fork, I noticed an unusual
abundance of the caddisfly, Lopidostoma pluviale (Milne). In a more spatially
extensive examination of a population, I investigated distribution of this
caddisfly in the Blue Mountain region of northeastern Oregon. L. pluviale was
more common and/or abundant further downstream than would be expected for
a shredding feeder based on the River Continuum Concept (Vannote, et al.,
1980). Through gut content analyses, I demonstrated that this species is much
more of a generalist feeder than its designation as a shredder would imply.
Consequently, its distribution is not limited to headwaters where allochthonous
food resources are abundant. I hypothesize that non-food environmental factors
may be more important in determining the distribution of this species.
Results of this research indicate that assemblage studies can reveal
interesting relationships with environmental conditions. In addition, paying
attention to unusual distributions of taxa in assemblage studies can lead to
further studies that can improve our understanding of the biology and ecology of
species. / Graduation date: 2004
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Geographic variation in genetic and meristic characters of coastal cutthroat trout (Oncorhynchus clarki clarki)Williams, Thomas Herbert 21 April 2004 (has links)
Graduation date: 2004
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A cooperative effort to track Humboldt squid invasions in OregonChesney, Tanya A. 04 September 2012 (has links)
Interannual variability of Humboldt squid (Dosidicus gigas) occurrence in the
northern California Current System is largely unknown. In Oregon, the distribution of
this versatile predator and what is influencing their range expansion from Mexico is
poorly understood due to the recent nature of their "invasion" and a lack of
monitoring. Humboldt squid are large predators that have the potential to affect
ecosystem structure and fisheries because of their high-energy demands and ability to
exploit a variety of oceanographic conditions and prey sources. Developing baseline
distribution information is a critical first step to assess their potential ecological,
social, and economic impacts, and to develop models to predict future range
expansion.
This study has two main objectives: (1) to document where and when
Humboldt squid have been present in Oregon through cooperative fisheries research,
and (2) to correlate the sightings with oceanographic conditions using a geographic
information system (GIS) and species distribution modeling (SDM). I conducted 54
interviews with local fishermen and aggregated their squid sightings with available
fishery-independent survey and fishery-dependent observer data from the National
Marine Fisheries Service. I compiled a total of 339 Humboldt squid sightings,
reported for the years 2002-2011 from the Oregon coast to 131�� west longitude.
Correlation analyses were performed for Humboldt squid sightings and sea surface
temperature (SST), chlorophyll a content (chla), sea surface height anomalies (SSH),
dissolved oxygen at 30 m depth (30 m DO), and sea surface salinity (SSS) using a
GIS, nonparametric multiplicative regression (NPMR) habitat modeling, and
maximum entropy modeling (Maxent). Results indicate that oceanographic conditions
have the potential to influence Humboldt squid occurrence, and in Oregon, sightings
vary temporally and spatially. Combining the sightings from fishermen and scientific
surveys greatly enhanced the spatial extent of the data. Humboldt squid were most
frequently observed between 124.4��W and 125��W in proximity to the shelf-break at
the 200 m isobath, with peak sightings (116) recorded in 2009 and the fewest (6)
reported in 2003 and 2011. The highest occurrence of Humboldt squid were observed
at a SST of 10.5-13.0��C, 0.26-3.0 mg m����� chla content, -4.0-1.0 m SSH anomalies,
32.2-32.8 psu SSS, and at 3-4.5 ml L����� and 6-7 ml L����� 30 m depth DO. Maps of
estimated likelihood of occurrence generated by NPMR were consistent with
overlayed observations from fishermen, which were not used in the model because
they were limited to presence-only information.
An interdisciplinary approach that incorporates cooperative fisheries research
and ecosystem-based management is necessary for monitoring Humboldt squid in
Oregon. Traditional methods are insufficient because Humboldt squid are data-poor,
highly migratory, and are main predators of many commercially important fisheries in
Oregon. Based on my findings, sightings recorded by fishermen covered a much
larger area over a longer time frame than the scientific survey and observer data, and
excluding their knowledge would have led to a different interpretation of Humboldt
squid distribution and environmental tolerances. Although there is uncertainty in the
data from potential map bias or misidentification of smaller Humboldt squid,
incorporating sightings from fishermen with traditional fisheries research increases the
quantity and quality of information. Cooperative monitoring for Humboldt squid
could include training in species identification and sea condition reporting in
logbooks. Future "invasions" are likely, and more eyes on the water will improve our
understanding of the behavior and impacts of Humboldt squid on coastal resources. / Graduation date: 2013
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Biogeographic and experimental evidence for local scale dispersal limitation in central Panamanian forest birdsMoore, Randall Phillips, 1965- 23 March 2006 (has links)
Graduation date: 2006 / I examined the avian biogeography of the islands of Lago Gatun, Panama, in an effort to better understand the effects of forest fragmentation in this biodiverse region, and specifically to understand the importance of fragment isolation and the mechanism behind its effects on tropical bird distribution. I combined exhaustive surveys of 29 islands with an experimental release program. Analyses of these data were conducted in a hierarchical fashion to evaluate evidence for avian dispersal limitation at multiple scales. First, I assessed the potential roles of area and isolation in determining avian species richness across this series of fragments, and how these relationships may differ for edge and forest dependent birds. Next, I analyzed community structure and species distributions to determine the relative contributions of island area and isolation in creating patterns of species-specific insular occurrence. Lastly, I assessed the results of the experimental investigation to evaluate the hypothesis that dispersal limitation explains the insular distribution patterns of several tropical forest birds. Isolation is a significant predictor of avian species richness, but only after accounting for the stronger effect of area. Species-isolation relationships are different in this archipelago for birds that rely on forest and edge habitats, respectively. Species-specific distributions are significantly nested when islands are ordered by area, and by isolation once the effect of area is considered. Occurrence of most forest species is sensitive to area and isolation of the archipelago. Examination of guild structure suggests that multiple mechanisms are responsible for these occurrence patterns. There are distinct species-specific differences in ability to cross small gaps, and species which are better able to cross these gaps are more widely distributed across the archipelago than those species that negotiate the same barriers poorly. Species that performed uniformly well in release experiments were much less likely to have suffered insular extinction in the preceding 25 years than those species that showed moderate to poor experimental performance. There is strong evidence of a morphological basis for the patterns. The cumulative evidence from these analyses is the most comprehensive evidence to date of local-scale dispersal limitation in volant birds.
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Biology of the Grey-headed gull Larus cirrocephalus in South Africa.McInnes, Alistair McIntyre. 26 November 2013 (has links)
The biology of the Grey-headed Gull was studied between 2004 and 2005 in South
Africa's Gauteng, KwaZulu-Natal and Northern Cape provinces.
Grey-headed Gulls have a widespread but patchy distribution in South Africa,
occurring both inland and at the coast. Their largest population is centred on Gauteng,
where the species appears to be a relatively recent colonizer and where the current
breeding population is estimated at 2185 breeding pairs (the largest in South Africa).
There is evidence that the species has also increased in other parts of South Africa,
especially at Port Elizabeth in the Eastern Cape. The majority of coastal birds are
found in KwaZulu-Natal and there is strong evidence for regular movements of adult
birds between Durban and Lake St Lucia. By contrast, little evidence was found for a
putative large-scale, regular movement between Gauteng and KwaZulu-Natal.
The breeding biology of the Grey-headed Gull was studied at four sites in Gauteng
and at Lake St Lucia's Lane Island during 2004 and 2005. The distance between the
Gauteng sites ranges from 1.7 km, between Lakefield Pan and Korsman's Bird
Sanctuary, to 25.3 km, between Bonaero Park and Modderfontein Pan. The
approximate distance between Gauteng and Lake St Lucia is 460 km. The mean
clutch size at all sites was 2.42 eggs and the mean incubation period was 24.9 days.
Parental investment in incubation was approximately equal between the sexes while
males spent more time in attendance and participated in more aggressive encounters.
Empirical growth curves are given for mass, wing, culmen, head and foot
morphometrics of Grey-headed Gull chicks. Intraspecific variation in breeding
parameters reveal significant differences between sites, including: highly synchronous
laying at Lake St Lucia; the largest eggs and fastest growing chicks at Gauteng's
Modderfontein Pan (a small, peripheral colony); and the smallest eggs and slowest
growing chicks at Gauteng's Lakefield Pan (a large, 'core' colony). Possible reasons
for these differences include the relative localities of each site in terms of feeding
opportunities, high levels of predation by African Fish Eagle's at Lane Island, and
density dependent factors operating on the large colonies within the core population
on Gauteng's East Rand. Overall daily egg survival was comparatively high for all
sites in Gauteng and low for Lane Island nests. Morphometric, plumage and bare-parts data from a sample of trapped and resighted
birds are used to age, sex and determine the timing and duration of moult in the Greyheaded
Gull. Six age classes were identified and, for all measurements, males were
significantly larger than females. The mean duration of primary moult was 136 days
between October and January and there were two waves of secondary moult. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2006.
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Sugarcane stem borers in Ethiopia : ecology and phylogeography.Assefa, Yoseph. January 2006 (has links)
Eldana saccharina Walker (Lepidoptera: Pyralidae) is an indigenous insect widely distributed throughout Sub-Saharan Africa that is a major pest of sugarcane in southern Africa. Studies have shown that populations from West Africa have distinct behavioural differences compared to populations from eastern and southern Africa. In addition, the parasitoid guilds attacking populations in these regions are markedly different. This marked behavioural and parasitoid guild variation evoked a hypothesis of genetic diversification. To evaluate this hypothesis a project on the phylogeography of E. saccharina was initiated. The project was planned to include sampling of as many regions as possible in its known range in Africa, to obtain specimens of E. saccharina for genetic analysis.
When these surveys were initiated in Ethiopia, it was found that there was no published literature available on the occurrence of stem borers in Ethiopian sugarcane. It was thus clear that no stalk borer/parasitoid surveys had been completed in either sugarcane or any large grass and sedge indigenous hosts in Ethiopia. The study was thus expanded beyond the investigation of only the genetic diversity of E. saccharina, to include area-wide surveys to determine ecological aspects of the borer complex in suspected host plants, including sugarcane, in Ethiopia. In this way the host plant range and distribution of E. saccharina and other sugarcane borers in Ethiopia in particular could be determined, samples for a larger phylogeography project could be collected, and the insect's impact on
sugarcane could be assessed.
Quantified area-wide surveys of the sugarcane estates and small-scale farmer fields of Ethiopia were conducted between December 2003 and February 2004. The surveys verified the presence of four lepidopteran stem borer species on Ethiopian sugarcane. These were Chilo partellus Swinhoe (Lepidoptera: Crambidae), Sesamia calamistis Hampson (Lepidoptera: Noctuidae), Busseola fusca Fuller (Lepidoptera: Noctuidae) and Busseola phaia Bowden (Lepidoptera: Noctuidae). The surveys indicated that Busseola species are the major and most widely distributed sugarcane stem borers in sugarcane farms of Ethiopia. Over 70% of the peasant sugarcane fields visited were infested by these borers, with the highest levels of infestation (35% and 50%) being in the northern and western part of the country, respectively. Busseola was also the predominant stem borer of sugarcane in two of the three estates (Wonji and Finchawa). Chilo partellus and S.calamistis were recovered in very low numbers at all the commercial estates and from peasant farms in the western part of Ethiopia. However, C. partellus was the predominant sugarcane stem borer in lowland areas of northern, southern and eastern parts of the country. Eldana saccharina was recovered from large sedges in waterways of Metehara and Wonji sugar estates in the central part of the country, and sedges growing around lakes in northern and southern Ethiopia, but not from sugarcane anywhere in Ethiopia.
The phylogeographic study conducted on E. saccharina populations from eleven countries of Africa clearly showed the population structure of the insect within the continent. Five hundred and two base pairs of the mitochondrial DNA (mtDNA), corresponding to the Cytochrome Oxidase subunit I (COl) region, were sequenced to clarify phylogenetic relationships between geographically distant populations from eastern, northern, southern and western Africa. Results revealed that E. saccharina is separated into four major populations corresponding to their geographical location, i.e. West African, Rift Valley and two southern African populations. Sequence divergence between the four populations ranged from 1% to 4.98%. The molecular data are congruent with an isolation by distance
pattern except for some of the specimens from eastern and southern Africa where geographically close populations are genetically distant from each other. Geographical features such as the Rift Valley and large water bodies in the continent seem to have a considerable impact on the genetic diversity in E. saccharina.
Identification of field-collected stem borer specimens was done using classical taxonomic techniques, except for Busseola spp. where DNA barcoding was used. As field-collected larval material of Busseola died before reaching the adult stage, identification of species using adult morphology was not possible. 'Sequence divergence in the COl gene was used as a tool to identify the species of Busseola attacking Ethiopian sugarcane. Partial COl sequences from Ethiopian specimens were compared with sequences of already identified noctuid species from the East African region. Results of the sequence analysis indicated that the Busseola species complex in Ethiopian sugarcane comprised B. fusca and B. phaia. Sequence divergences between Ethiopian Busseola species was as high as 5.0 %, whereas divergences within species were less than 1% in both species identified.
Several larval parasitoids, bacterial and fungal diseases of stem boring caterpillars were also recorded in Ethiopian sugarcane. Amongst these was Cotesia flavipes Cameron (Hymenoptera: Braconidae). This exotic parasitoid has been introduced into several African countries for the control of C. partellus in maize and sorghum, but had never been released in Ethiopia. To investigate the origin of C. flavipes in Ethiopian sugarcane, molecular analyses were conducted on Ethiopian specimens from sugarcane and specimens of C. flavipes from different countries of Africa released from the Kenyan laboratory colony, again using COl sequences. Results of the analysis revealed that the C. flavipes population that had established in sugarcane fields of Ethiopia was similar to the south east
Asian populations released against C. partellus in maize in other parts of Africa, and different from other populations of this species, providing evidence that the Ethiopian C. flavipes is likely to be a descendant of the original Pakistani population that was released in different parts of Africa.
The study reveals the importance of lepidopteran stem borers in sugarcane production in Ethiopia and highlights the role of molecular methods in species identification and determining phylogenetic relationships. More importantly, this study establishes the continental phylogeographical pattern of the indigenous moth, E. saccharina. The impact of geological events, geographic barriers and cropping systems on the evolution, distribution and abundance of stem borers are discussed. Future areas of research for understanding more about the phylogeographic relationships of E. saccharina and management of stem borers are discussed. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2006.
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Water temperature and fish distribution in the Sabie River system : towards the development of an adaptive management tool.Rivers-Moore, Nicholas Andrew. January 2003 (has links)
Water temperatures are a fundamental water quality component, and a key abiotic determinant of fish distribution patterns in rivers. A river 's thermal regime is the product of a multitude of thermal drivers and buffers interacting at different temporal and spatial scales, including, inter alia, air temperatures, flow volumes (including groundwater flows and lateral inputs from tributaries), channel geomorphology and riparian vegetation. "Healthy" river systems are self-sustaining, with adequate thermal variability to maintain biotic diversity. Temporal variability of flow volumes and water temperatures, and how these change along the longitudinal axis of a river, contribute towards a rivers "signature". Rivers that have had their signatures altered through anthropogenic impacts may no longer be sustainable, and require varying levels of management. Successful river management should include a quantification of these signatures , a definition of the "desired" state which management aims to achieve, associated "thresholds" of change or concern, and monitoring programmes. Such an approach requires flexibility and adaptability, as well as appropriate tools being available to natural resource managers. Indices, the utility of which are enhanced when included in predicative modelling systems, are a common means of assessing system variability and change. The degree of confidence placed in such tools depends on the level of fundamental science, and the degree of system understanding, underpinning them. This research contributes to the understanding of the ecological significance . of water temperatures in variable semi-arid river systems, using the Sabie River (Mpumalanga, South Africa) as a case study, and indices derived from biological indicators (Chiloglanis , Pisces: Mochokidae) to quantify the effects of cumulative changes in heat units against a hypothesised critical water temperature threshold. Hourly water temperatures for 20002002 collected at nine sites in the main rivers of the Sabie catchment, together with biannual surveys of relative abundances and community patterns of fish collected using standard electrofishing techniques, were used to provide the basis for a modelling system which aims to provide river managers with a tool for quantifying changes to the thermal regime of the Sabie River. This modelling system consisted of a suite of pragmatic models, including multiple linear regression models for simulating daily maximum water temperatures, and simple cause-and-effect relationships between biological indices (change In condition factor and change in the ratio of relative abundances of two species of Chiloglanis) and annual metrics of time-of-exposure to heat stress. It was concluded that changes in the thermal regimes of the rivers in the Sabie catchment are likely to lead to changes in fish distribution patterns, and a decline in river health. Inherent system variability suggests that management decisions will be made in the face considerable uncertainty. Indirect management of water temperatures may be possible through maintenance of flow volumes and flow variability. However, the most appropriate management approach for maintaining fish diversity within these rivers is to ensure that obstacles to fish migration are minimized, to maximise the ability of river biota to respond to thermal changes, by accessing suitable alternative habitats or refugia. Future research should focus on extending the time series of water temperatures from such river systems, and further understanding the drivers and buffers contributing to the thermal regimes of variable semi-arid river systems in South Africa. Additional testing of the validity of the hypothesized relationships between abiotic processes underpinning biotic patterns should be undertaken. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 2003.
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