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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Assessment of Chimpanzee (Pan troglodytes) population and habitat in Kwitanga Forest, western Tanzania.

Ndimuligo, Sood A. 11 April 2008 (has links)
This study examined three aspects: estimation of chimpanzee (Pan troglodytes) population size using nest density as a proxy, description of the plant community and assessment of human impacts to chimpanzee habitat in Kwitanga forest, western Tanzania. The overall estimated mean chimpanzee population density was 0.69(0.31–1.54) individuals per km2 and a mean population size of 15(7-34) weaned individual chimpanzees in the forest. The natural vegetation in Kwitanga consists mainly of miombo woodland, dominated by Brachystegia-Julbernadia tree species, poorly developed riverine forest, cultivated land and oil palm plantation. Assessment of the abundance of nesting trees in the landscape revealed that tree species composition along transects were significantly different to nesting sites (trees surrounding the actual tree that contains a nest) (Kolmogorov-Smirnov test: KSa = 2.0148; D = 0.3934: P < 0.05). Thirteen tree species were used for nests; the most used species were B. bussei, B. utilis, B. mirophylla, J. globiflora and P. tinctorius. The assessment on scarcity of nesting tree species in the landscape revealed that such species were abundant by proportion (KSa = 0.5883; D = 0.2308; P > 0.05), and species-specific density (Wilcoxon Z-test: Z = - 1.0265; U1= U2 = 13; p > 0.05). Trees in size classes between 10 cm and 40 cm diameter dominated the forest. The study on size suitability showed that there were significant differences (using ANOVA with Tukey’s HSD post hoc test) in tree diameter size among the three groups: transects, nesting sites, and nesting trees. Nesting trees were unique in size to the other two groups. The mean size of nesting trees was larger compared to both nesting sites and transects (27 ± 1.1 cm; 23 ± 0.7 cm and 18 ± 0.5 cm) respectively. Similar differences existed in tree densities between nesting sites and transects (Wilcoxon test: Z = 1.8104; U1 = 46, U2 = 61: P< 0.05), with nesting sites presenting higher tree density. These results indicated scarcity in trees of a size suitable for nesting, and nesting materials.. Nesting tree species occur in the landscape, though their sizes and higher tree species density at nesting sites determined nesting location choice and specific nesting tree selection. Tree felling indicated by stumps was the major threat to the availability of suitable nesting trees, with a higher encounter rate of seven (7) stumps per km and contributed 48 % of total human disturbance, followed by established fields in the forest. The analysis on the direction of the major threat to the habitat revealed that, the main road cutting through the forest is a key to tree felling. Encountered stumps declined with increased distance from the main road towards the forest edge, with more stumps in between 0 -100 m (P< 0.05; log (Y) = 1.7017 - 0.0007(X); R2 = 0.6705). Such findings implied that the prison inside the forest is a iii major cause of habitat decline. At least 30 tree species constituted the group of stumps. Julbernadia globiflora and Uapaca kirkiana were the most felled tree species. High human disturbances implied by higher human activities encounter rates, and overlapping tree size classes between felled and standing trees were the major threats to chimpanzee habitat in Kwitanga forest. High chimpanzee density and population size estimates in Kwitanga forest renders this area a potential for conservation in the Greater Gombe Ecosystem Program. Kwitanga being the largest remaining natural forest near Gombe National Park, it will increase habitat size to allow chimpanzee dispersal and feeding area. Such movements across heterogeneous landscapes would allow long-term survival through reduced competition, increased genetic diversity and ability to absorb minimal environmental shocks
2

The effects of land use on stream communities in highland tropical Nigeria

Umar, Danladi January 2013 (has links)
Globally, stream invertebrate communities have been shown to respond to habitat degradation as a result of land use hanges. The effects of land use changes on stream communities have been well documented in temperate regions, however, their effects in the tropics are relatively unknown, particularly where land use activities can differ markedly (e.g., tea, maize and Eucalyptus plantations). To understand how land use affects tropical highland Nigerian stream communities, I surveyed 55 second and third order streams across four land use categories, ranging from continuous tropical montane forest to intensive crops/pasture. Streams were sampled in the dry season (October to March) for physico-chemical parameters (i.e., temperature, pH, conductivity, turbidity, current velocity, channel morphometry and riparian characteristics) and ecological characteristics (i.e., fine particulate organic matter [FPOM], coarse particulate organic matter [CPOM], algae and benthic invertebrates). Water temperature in all streams was high (up to 25oC) while levels of dissolved oxygen were frequently low (15–79 %). Physico-chemical conditions varied across land uses with continuous forested streams being cooler, with higher dissolved oxygen, larger bed substrate and more stable channels. Similarly, benthic invertebrate communities showed a strong response with the highest taxonomic diversity in forested streams and the lowest in streams within intensive crops (e.g., cabbage crops). Several of the taxa which occurred in forested streams (e.g., the mayflies Heptageniidae and Oligoneuridae and brachyuran crabs) were rare or absent in streams with more intensive land use. In contrast, damselflies and several true bugs (e.g., Notonectidae and Corixidae) were rare in forested streams but more common in other land uses. In order to test land use impacts on stream processes leaf litter decomposition experiments were carried out in nine streams, three in forest, three in tea plantations and three in maize fields. Leaf breakdown rates were slow compared with other reports for tropical streams, however leaves in forested streams broke down significantly faster (on a degree day basis) than in other land uses. This faster break down seemed to be driven by greater shredder densities in forested streams. Significantly lower densities of invertebrates were found in leaf bags incubated in streams draining tea plantation and maize fields than in forest streams. In the same nine streams food web components were sampled and analysed using gut content and stable isotope (N and C) analyses. Stream food webs in continuous forest were more complex than plantation and maize field streams. Stable isotope analysis indicated that primary consumers assimilated a mixture of autochthonous and allochthonous carbon resources, but the proportion varied among sites. Overall, my results suggest that in Nigerian highland tropical streams more intensive land use activities strongly affect the diversity and composition of benthic stream communities and ecosystem function, in similar ways to those reported in temperate streams.
3

Development of juvenile culture techniques and testing of potential biomarkers of environmental stress in freshwater mussels (Bivalvia: Unionidae)

Beaty, Braven B. 05 October 2007 (has links)
The freshwater mussel fauna of the Clinch River in Southwest Virginia has declined in recent decades, principally due to habitat degradation from poor land-use patterns and pollutants. A study was undertaken to determine the feasibility of using river water in a flow-through culture system to rear juvenile freshwater mussels. The culture method placed juvenile mussels, confined in small dishes, into oval troughs supplied with untreated river water. Two of three years produced acceptable survival rates of 27% and 19% to an age of 90 days or greater. The third year yielded very low survival rates of less than 3%, demonstrating that failures in culture production can occur. Growth rates of juveniles in the culture system using river water were almost double those in laboratory culture systems, provided that juveniles were placed in the oval troughs during June. Otherwise, growth was comparable to that attained in laboratory culture systems. / Ph. D.
4

Ecology of freshwater mussels in disturbed environments

Österling, Martin January 2006 (has links)
<p>The number of species extinctions is increasing at an alarming rate. Long-lived freshwater mussels of the order Unionoida, which include a parasitic stage on a host fish, are highly threatened. Habitat degradation by turbidity and sedimentation is thought to be one major reason for their decline. The objective of this thesis was to examine recruitment patterns and identify the causes of the lack of recruitment in the threatened unionoid freshwater pearl mussel (Margaritifera margaritifera). In addition, I investigated the effects of turbidity on non-endangered dreissenid mussels, where turbidity was manipulated through use of bioturbating mayflies.</p><p>In a survey of 107 Swedish streams, mussel population size and trout density were both positively correlated to recruitment probability of M. margaritifera. A more in-depth study of the age-structure of nine populations revealed that four of these populations showed no signs of recruitment over the last ten years. Within-stream variation in recruitment was high as both mussels and trout had patchy distribution, and may be important for population regulation. Moreover, examination of different life stages revealed no differences in the gravid mussel stage or the stage when mussels infect salmonid fish. Instead, differences were observed for the juvenile, benthic stage, presumably related to differences in turbidity and sedimentation. High turbidity may affect filter-feeding efficiency of mussels and high sedimentation may reduce survival by clogging sediments, thereby altering, for example, oxygen and food conditions. In the study of the effects of turbidity, bioturbating mayflies increased turbidity and filter-feeding dreissenid mussels reduced turbidity. Mussel growth both decreased and increased with increasing turbidity, depending on sediment type.</p><p>Turbidity and sedimentation often impact entire stream systems, and a holistic, catchment-based management strategy may be needed to reduce the effects of sedimentation on freshwater pearl mussels. The effects of restoration take a long time and must start soon if recruitment of mussels is to be re-established. Restoration may also be more urgent in some streams than in others, as the maximum age of M. margaritifera populations in my study differed by as much as 60 years. As mussel and trout densities seem to be important for recruitment success, one conservation method may be to concentrate mussels into sites where trout density is high.</p>
5

Ecology of freshwater mussels in disturbed environments

Österling, Martin January 2006 (has links)
The number of species extinctions is increasing at an alarming rate. Long-lived freshwater mussels of the order Unionoida, which include a parasitic stage on a host fish, are highly threatened. Habitat degradation by turbidity and sedimentation is thought to be one major reason for their decline. The objective of this thesis was to examine recruitment patterns and identify the causes of the lack of recruitment in the threatened unionoid freshwater pearl mussel (Margaritifera margaritifera). In addition, I investigated the effects of turbidity on non-endangered dreissenid mussels, where turbidity was manipulated through use of bioturbating mayflies. In a survey of 107 Swedish streams, mussel population size and trout density were both positively correlated to recruitment probability of M. margaritifera. A more in-depth study of the age-structure of nine populations revealed that four of these populations showed no signs of recruitment over the last ten years. Within-stream variation in recruitment was high as both mussels and trout had patchy distribution, and may be important for population regulation. Moreover, examination of different life stages revealed no differences in the gravid mussel stage or the stage when mussels infect salmonid fish. Instead, differences were observed for the juvenile, benthic stage, presumably related to differences in turbidity and sedimentation. High turbidity may affect filter-feeding efficiency of mussels and high sedimentation may reduce survival by clogging sediments, thereby altering, for example, oxygen and food conditions. In the study of the effects of turbidity, bioturbating mayflies increased turbidity and filter-feeding dreissenid mussels reduced turbidity. Mussel growth both decreased and increased with increasing turbidity, depending on sediment type. Turbidity and sedimentation often impact entire stream systems, and a holistic, catchment-based management strategy may be needed to reduce the effects of sedimentation on freshwater pearl mussels. The effects of restoration take a long time and must start soon if recruitment of mussels is to be re-established. Restoration may also be more urgent in some streams than in others, as the maximum age of M. margaritifera populations in my study differed by as much as 60 years. As mussel and trout densities seem to be important for recruitment success, one conservation method may be to concentrate mussels into sites where trout density is high.
6

Impactos da intervenção do projeto Doces Matas em comunidades de Mata Atlântica : perspectiva de um estudo de percepção ambiental

Barreto, Karla Fernanda Barbosa 28 February 2008 (has links)
The Brazilian Atlantic Forest is one of the World´s most biologically diverse biomes, and encompasses a variety of different forest formations and ecosystems, originally covering 15% of Brazilian territory. However, the whole area has suffered significant anthropogenic degradation, and the forest has now been reduced to less than a tenth of its original cover. The state of Sergipe is typical of this scenario, and remaining habitat is distributed in a few dozen small, isolated fragments of forest, which harbour a characteristic fauna, including endangered species such as Coimbra´s titi monkey, Callicebus coimbrai. In addition to threatening its biodiversity, the degradation of these forests has a number of negative implications for local human populations, in particular with regard to the protection of water supplies, and related consequences for subsistence activities, health, and quality of life. There is a clear need to involve local residents in any project, and to integrate them as allies against the traditional view of environmental preservation as an obstacle to development. The present study was based on a systematic analysis of the environmental perception of the participants in an environmentally-oriented social development project Projeto Doces Matas in three rural communities of eastern Sergipe (Badajós, Caraíbas and São Sebastião). While the majority of subjects had little knowledge of the environment or environmental legislation, they were able to comprehend their dependence on Nature, and in particular its protection of water supplies. There was a clear relationship between the proximity of local forests and their exploitation by the members of local communities, and the attitudes of local residents towards their preservation. Following a series of activities aimed at increasing the sensitivity of the participants towards the environment, many subjects were able to answer specific questions they had been unable to respond correctly before the activities. This reveals the need for a systematic process of environmental education, which should involve the whole community. The communities appear to be willing to preserve the environment, but are forced into the exploitation of natural resources by their lack of financial assets. The provision of ecologically-sustainable alternative sources of income such as beekeeping, the activity promoted by Doces Matas is a clear priority for these communities. / A Mata Atlântica possui um dos maiores índices de diversidade biológica do planeta, e abrange um conjunto variado de formações florestais e ecossistemas associados, originalmente cobria 15% do território brasileiro. Entretanto, toda a área sofreu uma degradação antrtópica significativa, e a floresta agora está reduzida a menos de 10 % de sua cobertura original. O Estado de Sergipe é um exemplo típico deste cenário, restando apenas algumas dezenas de fragmentos pequenos e isolados de floresta, que abrigam uma fauna característica, que inclui espécies ameaçadas de extinção, como o guigó-de-sergipe, Callicebus coimbrai. A degradação destas matas, além de colocar em risco toda a sua biodiversidade, implica em uma redução crítica na disponibilidade de água para as populações humanas locais, e conseqüências deletérias para suas atividades de subsistência, saúde e qualidade de vida. É clara a necessidade do envolvimento dos moradores no processo de preservação ambiental, e de integrá-los como aliados, para combater a visão de que a preservação ambiental consiste em entrave ao desenvolvimento. O presente estudo baseou-se numa análise sistemática da percepção ambiental dos participantes de um projeto sócioambiental Projeto Doces Matas em três comunidades rurais do leste de Sergipe (Badajós, Caraíbas e São Sebastião), onde observou-se que os entrevistados não possuem muitas informações sobre meio ambiente, no entanto, são capazes de perceber a dependência que apresentam em relação à água e a natureza. Houve uma clara relação entre a proximidade do local da floresta e sua exploração pelos membros das comunidades, e as atitudes destes em prol da preservação da floresta. Após as atividades de educação ambiental, verificou-se um aumento da sensibilidade dos participantes em relação ao meio ambiente. Além disso, muitos sujeitos foram capazes de responder questões específicas, que não responderam corretamente antes das atividades. Isso demonstra a necessidade de um sistemático processo de educação ambiental que deve envolver toda a comunidade. As comunidades demonstram estar dispostas a preservarem o meio ambiente, mas necessitam explorar os recursos naturais pela falta de outras fontes de renda. O fornecimento de uma alternativa de renda ecologicamente sustentável como a apicultura, a atividade promovida pelo Doces Matas é uma prioridade clara para essas comunidades.
7

The Biodiversity Mirage: the Effects of Habitat Degradation and Exotic Predators on Ground-Dwelling Forest Birds, Tenrecs and Lemurs in Northeastern Madagascar

Murphy, Asia J. 03 June 2015 (has links)
Madagascar is one of the world's top conservation priorities due to the intense anthropogenic pressures on its diverse and endemic wildlife. There have been very few studies conducted in the largest protected area complex in Madagascar, the Masoala-Makira landscape (northeastern Madagascar). My goal was to examine the response of ground-dwelling forest birds, tenrecs (Lipotyphla: Tenrecidae) and lemurs to habitat degradation and the presence of exotic predators, and monitor population trends at resurveyed sites from 2008 to 2013. Using camera trap surveys and distance sampling, we observed 26 bird species (n = 4,083 observations), three spiny tenrec species (n = 244 observations) and 12 lemur species (n = 1,172 observations). Out of 13 focal species (seven bird, three tenrec and three lemur species), seven had higher point estimates of occupancy or density at intact forests when compared to intermediately degraded or degraded forest sites. Common tenrecs (Tenrec ecaudatus) and cathemeral lemurs changed their activity patterns, becoming more nocturnal in degraded forests. Feral cat (Felis sp.) trap success was negatively related to the detection of three bird species (red-breasted coua, Coua serriana; scaly ground-roller, Geobiastes squamiger; and Madagascar crested ibis, Lophotibis cristata). At two resurveyed sites (S02 and S05), out of 19 and 17 species, only four and eight species did not show consistent declines in occupancy or encounter rates, respectively, over a six-year period. This research highlights the urgent need for immediate conservation action in the Masoala-Makira protected area complex in order to protect one of the world's biodiversity hotspots. / Master of Science
8

Legacy Effects of Habitat Degradation by Lesser Snow Geese on Ground-Nesting Savannah Sparrows along the Hudson Bay Lowlands

Peterson, Stephen L. 01 May 2013 (has links)
Increased growth of the mid-continent population of Lesser Snow Geese (LSGO) has led to the degradation of coastal salt marsh and sedge meadow habitats across Canadian Arctic and sub-Arctic ecosystems. It is believed that a human-induced trophic cascade caused by agricultural habitat modification along migratory routes and wintering grounds has contributed to the increase in LSGO numbers, which has resulted in the alteration of habitat quality and connectivity along northern breeding and stopover sites used by various avian species. This habitat degradation has been shown to decrease the presence and temporal persistence of ground-nesting passerine and shorebird species at a local level and may lead to decreases of Arctic / sub-Arctic breeding avian species across landscapes that LSGO utilize and degrade. In 1999, four paired study plots were established, and used in conjunction with a single study plot from 1976, in order to measure the composition of habitat parameters (barren ground extent; graminoid and shrub cover) and to estimate the number of avian nests found in these plots. Using this historical data along with our findings from 2010 and 2011, our main objectives were to: 1) document the change in the aforementioned habitat parameters over time; 2) estimate the local nesting occupancy rates of the common Savannah Sparrow (SAVS), a robust and adaptable ground nester; and 3) determine which habitat variables are indicative of the rates of change and occurrence of nesting by SAVS within the study plots. By using ANOVA, linear mixed effects, and multi-state occupancy models, results suggest that an increase in barren ground, decreases in shrub and graminoid cover, and a loss of connectivity between suitable nesting patches has led to a 10% (λ = 0.90) annual decline in the probability that SAVS nesting occurred across the study plots from 1999 to 2010. These model results may be used to estimate long-term trends in persistence of breeding SAVS and other similar ground-nesting avian species that share habitats with LSGO along Arctic and sub-Arctic ecosystems. (93 pages)
9

Effects of habitat degradation on the evolutionary dynamics of populations in a rainforest cycad (Gymnospermae)

Lopez-Gallego, Cristina 18 May 2007 (has links)
In addition to habitat loss and fragmentation, habitat degradation can have important consequences for biodiversity and population persistence, including effects on ecological and genetic processes beyond decreased demographic viability and the loss of genetic variation. Particularly interesting is the potential for evolutionary changes and adaptation to degraded habitats, that can affect population viability even in the short-term. Here, I explore how environmental changes after habitat degradation affect the evolutionary dynamics of populations of the rainforest cycad Zamia fairchildiana, specifically how habitat degradation affects gene dispersal, inbreeding, directional selection, and genotype-by-environment interactions, and the potential for genetic differentiation between populations. Colonies of Z. fairchildiana showed little genetic differentiation in neutral molecular markers across study sites, thus can be considered as subpopulations. Subpopulations in the disturbed habitat are experiencing different environmental conditions when compared to subpopulation in their native habitat. Disturbed-habitat subpopulations showed a faster life-history. This faster life history is associated with a weaker spatial genetic structure and higher levels of inbreeding in the disturbed-habitat subpopulations. In addition, higher light availability in the disturbed habitat seems to be a major agent of selection on traits like leaf production that have the potential to respond to selection in these subpopulations. Different traits were under selection in the native-habitat subpopulations, suggesting the potential for genetic differentiation between native and disturbed-habitat subpopulations. Genotype by environment interactions in seed germination and seedling survival, in response to light and water availability, further suggested that subpopulations can adaptively diverge between habitats, but the relative role of genetic and environmental factors, particularly maternal effects, on the magnitude and rate of genetic differentiation between subpopulations remains to be evaluated. These results suggest that habitat degradation can have important consequences for the evolutionary dynamics of populations of this cycad, not necessarily typical of habitat loss and fragmentation. This study identified factors and processes important for population persistence in degraded habitats, but population responses to habitat degradation are complex. Thus further studies and long-term experiments are required for better understanding the effects of habitat degradation on population viability.
10

Declínio de aves no Arco do Desmatamento Amazônico / Bird decline in the Amazonian Arc of Deforestation

Middleton, Talitha da Cunha Pires 15 April 2016 (has links)
As florestas tropicais contêm mais da metade de todas as espécies terrestres existentes, mas sofrem com a crescente influência das atividades humanas. A destruição e a degradação de habitats são, atualmente, as principais ameaças à biodiversidade. Embora exista uma extensa literatura sobre extinção de espécies em paisagens antropizadas, muitos aspectos ainda foram pouco estudados. Desta forma, buscamos contribuir para o entendimento sobre: i) o atraso e as taxas de extinções locais de espécies após a perda e a fragmentação do habitat florestal; e ii) como as interações entre variáveis de fragmentação e de degradação do habitat (perda de qualidade do habitat) podem agravar a taxa de extinção local de espécies. Para responder a estas questões, amostramos grupos de aves em uma paisagem intensamente fragmentada ao norte do Estado do Mato Grosso, no Arco do Desmatamento Amazônico. Para quantificar o débito de extinção, inventariamos as espécies de papa-formigas em dez pontos de escuta, durante três dias, em 29 localidades amostrais, durante dois períodos separados por quase uma década. Avaliamos o legado do histórico de fragmentação da paisagem na extinção local de espécies por meio de um modelo que considera o tamanho do fragmento e o tempo desde o seu isolamento. Para investigar o papel das interações entre a degradação e a fragmentação de habitats na extinção de espécies, consideramos a assembleia de aves de sub-bosque, inventariadas por redes-de-neblina durante 14.400 horas em 30 localidades amostrais. Utilizamos a seleção de modelos para determinar quais interações e variáveis de degradação e de fragmentação são melhores preditoras do número de espécies, abundância e a composição da avifauna nos fragmentos. Nossos resultados revelaram que há duas etapas para a extinção de espécies: a extinção imediata e a extinção com atraso. Mesmo considerando a extinção com atraso, mais da metade das espécies desaparece em menos de duas décadas nos fragmentos, independentemente do tamanho do fragmento. Encontramos que a grande maioria das espécies nos fragmentos pequenos (<150 ha) foi extinta localmente logo após o isolamento, enquanto que nos fragmentos grandes, a perda de espécies ocorre com o tempo e as taxas de extinção local são mais elevadas. Ademais, os efeitos das interações entre as variáveis de degradação e fragmentação de habitat contribuem para a extinção local de espécies na paisagem estudada. Identificamos que o sinergismo entre o tamanho do remanescente florestal e a incidência de fogo é a principal causa da extinção de espécies nos fragmentos. No entanto, a abundância e a composição de espécies na comunidade foram, principalmente, influenciadas pelas interações aditivas entre o tamanho do fragmento e a presença de gado. Observamos também que as alterações causadas pela presença do gado nos fragmentos resultam na substituição de espécies especialistas de habitat florestal e típicas de sub-bosque por espécies que habitam o dossel, bordas e áreas perturbadas. As implicações de nossos resultados para a conservação são: o intervalo de oportunidade para mitigação dos efeitos da fragmentação e perda de habitat, sobre os papa-formigas, devido ao débito de extinção, mesmo que ainda presente, é muito curto para a implementação de ações eficazes para conservação, especialmente para os fragmentos pequenos, onde a perda da maioria das espécies ocorre imediatamente após o isolamento do fragmento. Portanto, ações de conservação deveriam otimizar seus esforços em fragmentos grandes (>150 ha), onde há maior chance de resguardar as espécies já comprometidas com a extinção. Além disso, as espécies nos fragmentos pequenos são negativamente e de forma mais intensa influenciadas pelos efeitos interativos com a incidência de fogo e penetração do gado. Concluímos que a preservação apenas dos remanescentes florestais não é suficiente para conservação da biodiversidade. Assim, as políticas públicas devem ser direcionadas à coibição de novos desmatamentos e queimadas, além do incentivo para a utilização de cercas ao redor dos remanescentes florestais em propriedades privadas / Tropical forests contain over half of all terrestrial species on Earth, but are succumbing to the growing impact of human activities. Habitat destruction and degradation are the main current threats to biodiversity. While there is an extensive literature on species extinction in human-modified landscapes, many aspects are yet to be explored. This study aims to contribute to our understanding of (i) the rates of time-lagged local extinctions of species in the aftermath of habitat loss and fragmentation; and (ii) the combined effects of habitat fragmentation and degradation (i.e. reduction in habitat quality) in aggravating rates of local extinctions. To develop this research, we sampled different functional groups of forest birds within an intensively fragmented landscape representative of the Arc of Deforestation of southern Brazilian Amazonia. To quantify the magnitude of extinction debt we inventoried antbirds at 29 forest sites during two periods, separated by nearly a decade. At each site, we carried out ten standardized point-counts over three days, which were validated with simultaneous digital recordings. We examined species extinction rates induced by historical landscape fragmentation using a model that considers forest fragment size and time since their isolation. In relation to interactions between habitat degradation and fragmentation, we considered all understorey birds inventoried by mist-nets during 14,400 hours at 30 sampling locations. We used model selection to determine which metrics and interactions of forest degradation (intensity of fires, selective logging and cattle presence within the forest remnants) and fragmentation (fragment size, amount of surrounding forest cover) best predicted the number, abundance and composition of species in the fragments. Our results revealed that there are two main stages for species extinctions: immediately after and time-lagged forest isolation. Even where there is a delay in species extinctions, over half of all species disappeared within less than two decades post-isolation, regardless of forest fragment size. We also found that the majority of species in small fragments (<150 ha) disappear immediately after isolation, whereas species losses in large fragments occur over time and they present higher local extinction rates. Moreover, interactions between habitat degradation and habitat fragmentation contributed to the local species extinctions in the studied landscape. Forest patch size operated synergistically with fire incidence as the main cause of local extinctions in fragments. However, the composition and abundance of species was influenced by the additive interactions between fragment size and cattle intrusion, which resulted in the replacement of understorey forest specialists with generalist species typically found in disturbed areas. The conservation implications of our results include: there is a narrow window of opportunity for mitigating the effects of habitat loss and fragmentation on antbirds, especially for small fragments, where most species were lost immediately after isolation. Conservation actions should be focused on large fragments (> 150 ha) where there is greater potential for retaining species committed to extinction. Also, species in small fragments were more affected by the detrimental effects of fire incidence and cattle intrusion. We therefore conclude that the preservation of remaining forest fragments in itself is not enough for forest biodiversity conservation; public policy should be directed to fire suppression and fencing to deter cattle access to remaining forest fragments within private proprieties

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