Territórios resultam de competição por interferência que leva ao uso exclusivo do espaço. A territorialidade então depende da variação espaço-temporal na disponibilidade de recursos e está, geralmente, associada ao sistema de acasalamento. A defesa de território deve ocorrer quando os benefícios superam os custos, e essa relação custo-benefício deve ser afetada por fatores ecológicos (disponibilidade de recursos e densidade populacional), assim como variações individuais (sexo e maturidade) e sazonais (época reprodutiva) que determinam quais e quando os recursos são importantes. Embora as estratégias territoriais dos indivíduos devam variar com as condições ambientais, potencialmente levando a diferentes sistemas territoriais⁄ de acasalamento em diferentes populações, estudos prévios sobre territorialidade geralmente avaliam somente uma população e⁄ou consideram condições ambientais relativamente homogêneas. Utilizando um banco de dados extenso de captura-marcação-recaptura em 9 populações de um roedor generalista (Akodon montensis), e usando a sobreposição da área de vida como proxy de não-territorialidade, pretendemos entender os determinantes ecológicos, individuais e sazonais das estratégias territoriais dos indivíduos, e avaliar se a variação nas estratégias individuais pode levar a uma transição entre sistemas territoriais⁄ de acasalamento. Como previsto, identificamos que a sobreposição das áreas de vida foi maior entre machos do que entre fêmeas e aumentou com a densidade populacional. Também aumentou de machos imaturos para machos maduros, mas diminuiu de fêmeas imaturas para fêmeas maduras, sugerindo que a diferença na territorialidade entre os sexos é definida após a maturidade sexual. O efeito negativo da disponibilidade de fêmeas na sobreposição da área de vida entre machos foi mais forte na época reprodutiva, como esperado. Mais importante, no entanto, o efeito da disponibilidade de fêmeas na sobreposição da área de vida foi fortemente dependente do sexo. À medida que a disponibilidade de fêmeas aumenta, a sobreposição da área de vida aumentou entre fêmeas, mas diminuiu entre machos, indicando que quando as fêmeas deixam de defender território (e ficam mais agregadas) devido ao aumento da competição entre elas, os machos passam a defender território. Nosso estudo ressalta que as estratégias territoriais são muito variáveis entre indivíduos, o que é consistente com a plasticidade ecológica e fisiológica em Akodon montensis reportada em outros trabalhos, e sugere que diferenças suficientes nas condições ambientais podem levar à transição entre sistemas territoriais⁄ de acasalamento / Territories result from interference competition that leads to exclusive use of space. Territoriality thus depends on the spatial and temporal variation in resource availability, and is usually associated with mating systems. Territorial defense should occur when benefits outweigh costs, and this balance should be determined by ecological factors (resource availability and population density), as well as individual (gender and sexual maturity) or seasonal (breeding season) variations that determine which and when resources are important. Although individual territorial strategies should vary with changing environmental conditions, possibly leading to multiple territorial⁄mating systems among populations, previous studies on territoriality focused mostly on single populations and/or on relatively homogeneous environmental conditions. Relying on an extensive capture-recapture dataset from 9 populations of a generalist rodent (Akodon montensis), and using home range overlap as a proxy of non-territoriality, we aim to understand the ecological, individual and seasonal determinants of individual territorial strategies, and investigate whether variation in individual strategies can lead to transitions between territorial⁄mating systems. We identified that home range overlap was larger between males than females and increased with population density, as expected. It also increased from immature to mature individuals among males, but the opposite was true among females, suggesting that differences in territoriality between genders is established after sexual maturity. The negative effect of female availability on home range overlap between males was stronger in the breeding season, as expected. More importantly, though, the effect of female availability on home range overlap was strongly gender dependent. As female availability increased, home range overlap increased between females but decreased between males, suggesting that when females become non-territorial (and thus more aggregated) because of increased competition with other females, males become territorial. Our study highlights territorial strategies are extremely variable among individuals, which is consistent with previously reported ecological and physiological plasticity in Akodon montensis, and suggests that sufficient changes in environmental conditions could lead to transitions between territorial⁄mating systems

Para avaliar a quantidade ótima de energia e recursos a ser investida em reprodução, um animal deve não só acessar informações sobre sua própria condição corporal, como acessar também informações sobre coespecíficos presentes no ambiente em que vive. Este trabalho investigou essas duas vias (endógena e exógena) de obtenção de informação. Utilizando como organismo modelo a aranha Paratrechalea ornata (Trechaleidae), uma espécie em que os machos produzem presentes nupciais, este estudo investigou: (a) se machos investem mais tempo de busca quando na presença de pistas químicas de fêmeas virgens; (b) se machos aumentam ou diminuem o investimento na produção do presente nupcial quando há pistas da presença de machos competidores; (c) se restrições alimentares impõem efeitos de curto e longo prazo sobre o comportamento de construção de presentes nupciais. Machos mostraram preferência por locais com pistas da presença de fêmeas, mas não diferenciaram pistas de fêmeas virgens e copuladas. Diante de pistas da presença de um macho competidor, machos produziram presentes de menor qualidade, com menos seda. Por fim, restrições alimentares provocam efeitos de curto e longo prazo no comportamento reprodutivo dos machos, diminuindo a frequência de produção do presente nupcial e o tamanho do presente construído. Conjuntamente, os três experimentos realizados mostram que machos de P. ornata utilizam tanto informações exógenas quanto endógenas para ajustar seu investimento em reprodução. A combinação das informações obtidas deve aumentar a eficiência no gasto de energia, maximizando o sucesso reprodutivo dos machos sem que isso prejudique a manutenção de seu organismo / To evaluate the optimal amount of energy and resources to be invested in reproduction, animals should not only obtain information about their own body condition, but they should also obtain information about conspecifics in the environment where they live. This study investigated these two ways (endogenous and exogenous) of acquiring information. Using as model organism the spider Paratrechalea ornata (Trechaleidae), a species in which males produce nuptial gifts, this study investigated: (a) if males invest more time searching for sexual partners in the presence of chemical cues of virgin females; (b) if males increase or decrease the investment in nuptial gift construction in the presence of chemical cues of competitor males; (c) if food deprivation imposes short- and long-term effects on nuptial gift construction. Males showed a preference for sites with cues of females, but they did not discriminate cues of virgin from cues of copulated females. When males detected cues of a male competitor, they produced lower quality gifts, with less silk. Finally, food deprivation imposed both short- and long-term negative effects on male reproductive behavior, decreasing the frequency of nuptial gift construction and also the size of the gift. Together, the three experiments show that males of P. ornata use both exogenous as endogenous information to adjust their investment in reproduction. The combination of information obtained may increase the efficiency in energy use, maximizing male reproductive success without compromising self maintenance

Ainda que existam diversos registros de formas extremas de dimorfismo sexual, a função do alongado quarto par de pernas nos machos de muitas espécies de opiliões permanece desconhecida. Neste estudo, testamos quatro previsões sobre a hipótese de que a seleção sexual está direcionando o alongamento do quarto par de pernas nos machos de Longiperna zonata e Promitobates ornatus: (1) o coeficiente alométrico do comprimento do fêmur IV em machos será maior do que o das fêmeas; (2) machos com pernas IV mais compridas vão residir próximos a grupos de fêmeas; (3) machos envolvidos em interações agressivas terão fêmures mais compridos do que o tamanho médio da população; (4) a diferença de tamanho de perna entre os oponentes será menor do que a diferença esperada entre pares de machos escolhidos ao acaso na população. Como o previsto, o coeficiente alométrico do fêmur IV foi significativamente maior em machos do que em fêmeas nas duas espécies. O comprimento do fêmur IV está positivamente relacionado à chance de um macho ser encontrado próximo a um grupo de fêmeas. Finalmente, a média do comprimento do fêmur IV dos machos envolvidos em brigas foi significativamente maior que a de machos selecionados ao acaso da população. Adicionalmente, a média da diferença de tamanho entre pares de machos que brigaram foi significativamente menor que a média da diferença de tamanho de perna entre pares de machos selecionados ao acaso na população. Assim, a seleção sexual na forma de competição entre machos parece estar direcionando o dimorfismo sexual extremo no comprimento do fêmur nessas duas espécies de opiliões. / Although there are many reports of extreme forms of sexual dimorphism in harvestmen, the function of the elongated fourth pair of legs in males of many species remains unknown. We tested four predictions to address the hypothesis that sexual selection is driving the enlargement of the fourth pair of legs in males of Longiperna zonata and Promitobates ornatus: (1) the allometric coefficient of femur IV length in males will be higher than in females; (2) males with longer legs IV will reside closer to groups of females; (3) males involved in aggressive interactions will have longer femur IV than the population average size; (4) the size difference between contenders will be smaller than the difference expected between randomly chosen pairs of males in the population. As predicted, the allometric coefficient of femur IV length was significantly higher in males than in females of both species. Femur IV length was positively related to the chance of a male being found close to a group of females. Finally, the mean femur IV length of the males involved in fights was significantly larger than the mean of random samples of males from the population, and the average difference between male contenders was smaller than the average random expected difference of the population. Therefore, sexual selection in the form of male-male competition seems to be driving the extreme sexual dimorphism in femur length in these species.

Territórios resultam de competição por interferência que leva ao uso exclusivo do espaço. A territorialidade então depende da variação espaço-temporal na disponibilidade de recursos e está, geralmente, associada ao sistema de acasalamento. A defesa de território deve ocorrer quando os benefícios superam os custos, e essa relação custo-benefício deve ser afetada por fatores ecológicos (disponibilidade de recursos e densidade populacional), assim como variações individuais (sexo e maturidade) e sazonais (época reprodutiva) que determinam quais e quando os recursos são importantes. Embora as estratégias territoriais dos indivíduos devam variar com as condições ambientais, potencialmente levando a diferentes sistemas territoriais⁄ de acasalamento em diferentes populações, estudos prévios sobre territorialidade geralmente avaliam somente uma população e⁄ou consideram condições ambientais relativamente homogêneas. Utilizando um banco de dados extenso de captura-marcação-recaptura em 9 populações de um roedor generalista (Akodon montensis), e usando a sobreposição da área de vida como proxy de não-territorialidade, pretendemos entender os determinantes ecológicos, individuais e sazonais das estratégias territoriais dos indivíduos, e avaliar se a variação nas estratégias individuais pode levar a uma transição entre sistemas territoriais⁄ de acasalamento. Como previsto, identificamos que a sobreposição das áreas de vida foi maior entre machos do que entre fêmeas e aumentou com a densidade populacional. Também aumentou de machos imaturos para machos maduros, mas diminuiu de fêmeas imaturas para fêmeas maduras, sugerindo que a diferença na territorialidade entre os sexos é definida após a maturidade sexual. O efeito negativo da disponibilidade de fêmeas na sobreposição da área de vida entre machos foi mais forte na época reprodutiva, como esperado. Mais importante, no entanto, o efeito da disponibilidade de fêmeas na sobreposição da área de vida foi fortemente dependente do sexo. À medida que a disponibilidade de fêmeas aumenta, a sobreposição da área de vida aumentou entre fêmeas, mas diminuiu entre machos, indicando que quando as fêmeas deixam de defender território (e ficam mais agregadas) devido ao aumento da competição entre elas, os machos passam a defender território. Nosso estudo ressalta que as estratégias territoriais são muito variáveis entre indivíduos, o que é consistente com a plasticidade ecológica e fisiológica em Akodon montensis reportada em outros trabalhos, e sugere que diferenças suficientes nas condições ambientais podem levar à transição entre sistemas territoriais⁄ de acasalamento / Territories result from interference competition that leads to exclusive use of space. Territoriality thus depends on the spatial and temporal variation in resource availability, and is usually associated with mating systems. Territorial defense should occur when benefits outweigh costs, and this balance should be determined by ecological factors (resource availability and population density), as well as individual (gender and sexual maturity) or seasonal (breeding season) variations that determine which and when resources are important. Although individual territorial strategies should vary with changing environmental conditions, possibly leading to multiple territorial⁄mating systems among populations, previous studies on territoriality focused mostly on single populations and/or on relatively homogeneous environmental conditions. Relying on an extensive capture-recapture dataset from 9 populations of a generalist rodent (Akodon montensis), and using home range overlap as a proxy of non-territoriality, we aim to understand the ecological, individual and seasonal determinants of individual territorial strategies, and investigate whether variation in individual strategies can lead to transitions between territorial⁄mating systems. We identified that home range overlap was larger between males than females and increased with population density, as expected. It also increased from immature to mature individuals among males, but the opposite was true among females, suggesting that differences in territoriality between genders is established after sexual maturity. The negative effect of female availability on home range overlap between males was stronger in the breeding season, as expected. More importantly, though, the effect of female availability on home range overlap was strongly gender dependent. As female availability increased, home range overlap increased between females but decreased between males, suggesting that when females become non-territorial (and thus more aggregated) because of increased competition with other females, males become territorial. Our study highlights territorial strategies are extremely variable among individuals, which is consistent with previously reported ecological and physiological plasticity in Akodon montensis, and suggests that sufficient changes in environmental conditions could lead to transitions between territorial⁄mating systems

Para avaliar a quantidade ótima de energia e recursos a ser investida em reprodução, um animal deve não só acessar informações sobre sua própria condição corporal, como acessar também informações sobre coespecíficos presentes no ambiente em que vive. Este trabalho investigou essas duas vias (endógena e exógena) de obtenção de informação. Utilizando como organismo modelo a aranha Paratrechalea ornata (Trechaleidae), uma espécie em que os machos produzem presentes nupciais, este estudo investigou: (a) se machos investem mais tempo de busca quando na presença de pistas químicas de fêmeas virgens; (b) se machos aumentam ou diminuem o investimento na produção do presente nupcial quando há pistas da presença de machos competidores; (c) se restrições alimentares impõem efeitos de curto e longo prazo sobre o comportamento de construção de presentes nupciais. Machos mostraram preferência por locais com pistas da presença de fêmeas, mas não diferenciaram pistas de fêmeas virgens e copuladas. Diante de pistas da presença de um macho competidor, machos produziram presentes de menor qualidade, com menos seda. Por fim, restrições alimentares provocam efeitos de curto e longo prazo no comportamento reprodutivo dos machos, diminuindo a frequência de produção do presente nupcial e o tamanho do presente construído. Conjuntamente, os três experimentos realizados mostram que machos de P. ornata utilizam tanto informações exógenas quanto endógenas para ajustar seu investimento em reprodução. A combinação das informações obtidas deve aumentar a eficiência no gasto de energia, maximizando o sucesso reprodutivo dos machos sem que isso prejudique a manutenção de seu organismo / To evaluate the optimal amount of energy and resources to be invested in reproduction, animals should not only obtain information about their own body condition, but they should also obtain information about conspecifics in the environment where they live. This study investigated these two ways (endogenous and exogenous) of acquiring information. Using as model organism the spider Paratrechalea ornata (Trechaleidae), a species in which males produce nuptial gifts, this study investigated: (a) if males invest more time searching for sexual partners in the presence of chemical cues of virgin females; (b) if males increase or decrease the investment in nuptial gift construction in the presence of chemical cues of competitor males; (c) if food deprivation imposes short- and long-term effects on nuptial gift construction. Males showed a preference for sites with cues of females, but they did not discriminate cues of virgin from cues of copulated females. When males detected cues of a male competitor, they produced lower quality gifts, with less silk. Finally, food deprivation imposed both short- and long-term negative effects on male reproductive behavior, decreasing the frequency of nuptial gift construction and also the size of the gift. Together, the three experiments show that males of P. ornata use both exogenous as endogenous information to adjust their investment in reproduction. The combination of information obtained may increase the efficiency in energy use, maximizing male reproductive success without compromising self maintenance

Na presente tese estudei a biologia de Centris (Paracentris) burgdorfi, uma abelha solitária de ampla distribuição no Brasil. O único local de nidificação conhecido até o momento fica em uma área de dunas, no nordeste do Brasil, à 25 km da cidade de Natal. Neste local as fêmeas nidificam exclusivamente em paleodunas à cerca de 1 km do mar. Estudei o sistema de acasalamento da espécie, onde pude constatar que a alta competição por fêmeas próxima ao ninho faz com que o macho tenha que retirar a fêmea do local para conseguir o contato genital. Nenhuma fêmea foi vista acasalando mais de uma vez e, logo após a cópula a fêmea dá início à construção do ninho. O ninho é constituído de um túnel raso com acesso às células de cria, construídas uma ao lado da outra. Avaliei o número de viagens que a fêmea faz para a coleta de óleo e pólen e o tempo despendido em cada ação dentro do ninho (deposição de pólen, óleo, ovoposição e operculação). Durante o período de construção das células as fêmeas não dormem dentro do ninho, e sim, em ramos de Krameria tomentosa, a planta utilizada como fonte de óleo no local. Buscando ampliar nosso conhecimento sobre a espécie, procurei outras populações no Brasil para que pudesse avaliar o nicho trófico. Utilizei o pólen encontrado no corpo das fêmeas para inferir sobre a dieta parcial de adultos e imaturos. Além da área de dunas, no Nordeste, encontramos C. burgdorfi no cerrado em Cavalcante, Goiás e em áreas de campo de altitude, em Ponta Grossa, Paraná. Através da análise polínica, constatei a importância de plantas do gênero Chamaecrista como fonte de pólen, sendo este um dos poucos gêneros compartilhados entre os três locais. Krameria grandiflora foi a fonte de óleo em Cavalcante e em Natal, e Angelonia integérrima, foi a fonte de óleo no Paraná. Isso revela a amplitude de nicho trófico em C. burgdorfi não apenas em relação às espécies de plantas utilizadas na dieta mas, também, quanto ao tipo de elaióforo que a fêmea consegue acessar (epitelial e tricromático). Esta plasticidade possibilita a ampla distribuição da espécie em diferentes fitofisionomias. Analisei nutricionalmente a dieta na provisão da cria de C. burgdorfi do nordeste do Brasil e de células de cria de Centris (Paracentris) pallida, coletadas no sudoeste dos Estados Unidos. Centris pallida é uma espécie de Centridini que perdeu o comportamento da coleta de óleo. Centris burgdorfi possui uma dieta mais rica em lipídeos e proteínas, sendo a dieta de C. pallida mais rica em carboidratos. A dieta mais protéica de C. burgdorfi se deve à presença de Chamaecrista já que plantas que anteras poricidas contem mais proteínas em comparação às não-poricidas, como é o caso das fontes de pólen de C. pallida (Parkinsonia e Olneya) / In the present thesis, I studied the biology of Centris (Paracentris) burgdorfi, a solitary bee of wide distribution in Brazil. The only nesting site known is in a dune area in northeastern Brazil, 25 km from the city of Natal. In this place, the females nest exclusively in petrified dunes about 1 km from the sea. I studied the mating system of the species, where I could verify that the high competition by females near the nest forces the male to carry the female to another place to mate. No female was seen mating more than once and, soon after copulation, the female begins to construct the nest. The nest consists of a shallow tunnel with access to the brood cells. I evaluated the number of trips that the female made to the collection of oil and pollen and the time spent in each action within the nest (depositions of pollen, oil, oviposition and operculation). During the period of construction of the cells the females do not sleep inside the nest, but in branches of Krameria tomentosa, the plant used as source of oil. In order to increase our knowledge about the species, I searched for other populations in Brazil so that I could evaluate the trophic niche. I used pollen found in the body of females to infer about the partial diet of adults and immature. In addition to the dune area in the Northeast, I found C. burgdorfi in the tropical Savanna (Cerrado) in Cavalcante, state of Goiás and in high altitude field areas, in Ponta Grossa, state of Paraná. Through pollen analysis, I verified the importance of plants of the genus Chamaecrista as a source of pollen, being this one of the few genera shared among the three sites. Krameria grandiflora was the source of oil in Cavalcante and in the Natal, and Angelonia integerrima, was the source of oil in the Ponta Grossa. This reveals the trophic niche amplitude in C. burgdorfi not only in relation to the species of plants used in the diet, but also to the type of elaiophore that the female can access (epithelial and trichromatic). This plasticity makes possible the wide distribution of the species in different phytophysiognomies. Nutritionally I analyzed the diet in the provision of C. burgdorfi offspring from northeastern Brazil and from the breeding cells of Centris (Paracentris) pallida collected in the southwestern United States. Centris pallida is a species of Centridini that has lost the behavior of the oil-collection. Centris burgdorfi has a diet richer in lipids and proteins, and the diet of C. pallida is richer in carbohydrates. The most proteinic diet of C. burgdorfi is due to the presence of Chamaecrista, since plants with poricidal anthers contain more proteins compared to non-poricidal ones, such as C. pallida (Parkinsonia and Olneya) pollen sources

<p>In this thesis, I examined variation in sex expression and mating patterns in the sexually polymorphic, wind-pollinated herb <i>Plantago maritima</i>. With a combination of field studies, greenhouse experiments, and genetic analyses, I (a) examined factors influencing sex ratio variation in gynodioecious plants (in which hermaphrodites and females coexist), (b) discovered variation in breeding system, (c) investigated density-dependence of seed production, and (d) documented genetic variation within and among populations close to the northern range margin in Europe. </p><p>In a survey of 104 <i>P. maritima</i> populations, I documented considerable variation in sex ratio (range 0-70% females, median 6.3% females). As predicted, females were more frequently missing from small than from large populations, and the variance in sex ratio increased with decreasing population size. Among twelve populations sampled for seed production, the frequency of females was positively related to relative fecundity of females and negatively related to population size. The results suggest that the local sex ratio is influenced both by the relative fecundity of females and hermaphrodites, and by stochastic processes in small populations.</p><p>A comparative field study showed that plant fecundity decreased with increasing distance to nearest pollen donor both within and among populations in an archipelago in southern Sweden, where self-incompatibility was confirmed in controlled crosses. In contrast, plant fecundity was overall higher and was not density-dependent in the Skeppsvik archipelago in northern Sweden, where controlled crosses showed that plants are self-compatible. The results were consistent with the prediction that evolution of self-fertility should reduce density-dependence of pollination success.</p><p>I quantified the genetic structure within and among populations from eastern Sweden and western Finland based on variation at four polymorphic microsatellite loci. The genetic diversity was low in northern Sweden, which may be the result of a history of small population sizes and periods of frequent self-fertilization.</p>

In this thesis, I examined variation in sex expression and mating patterns in the sexually polymorphic, wind-pollinated herb Plantago maritima. With a combination of field studies, greenhouse experiments, and genetic analyses, I (a) examined factors influencing sex ratio variation in gynodioecious plants (in which hermaphrodites and females coexist), (b) discovered variation in breeding system, (c) investigated density-dependence of seed production, and (d) documented genetic variation within and among populations close to the northern range margin in Europe. In a survey of 104 P. maritima populations, I documented considerable variation in sex ratio (range 0-70% females, median 6.3% females). As predicted, females were more frequently missing from small than from large populations, and the variance in sex ratio increased with decreasing population size. Among twelve populations sampled for seed production, the frequency of females was positively related to relative fecundity of females and negatively related to population size. The results suggest that the local sex ratio is influenced both by the relative fecundity of females and hermaphrodites, and by stochastic processes in small populations. A comparative field study showed that plant fecundity decreased with increasing distance to nearest pollen donor both within and among populations in an archipelago in southern Sweden, where self-incompatibility was confirmed in controlled crosses. In contrast, plant fecundity was overall higher and was not density-dependent in the Skeppsvik archipelago in northern Sweden, where controlled crosses showed that plants are self-compatible. The results were consistent with the prediction that evolution of self-fertility should reduce density-dependence of pollination success. I quantified the genetic structure within and among populations from eastern Sweden and western Finland based on variation at four polymorphic microsatellite loci. The genetic diversity was low in northern Sweden, which may be the result of a history of small population sizes and periods of frequent self-fertilization.

The aim of this study was to investigate the basis to male mating decisions in two related species of bitterling: Rhodeus ocellatus and R. amarus. Bitterling have a resource-based mating system; females lay eggs in the gills of live freshwater mussels and males fertilize the eggs by releasing sperm into the inhalant syphon of the mussel. Male bitterling perform courtship behaviour and aggressively defend mussels in a territory from which they exclude other males. Using laboratory and field experiments it was shown that male aggressive behaviour is inherited through additive maternal genes. Male aggression is also influenced by the number of conspecific males encountered in competition for a mussel, and by the degree of clustering of mussels. Limited availability of mussels results in stronger selection on traits males use in mating context: hence they are more aggressive, larger and more colourful. The differences in mating behaviours in different environments may indicate a conflict between male dominance and female choice, but have not led to reproductive isolation. Resource availability during ontogenesis and male density during embryogenesis, however, do not exert an effect on male aggressive behaviour. Red carotenoid-based nuptial coloration functions as an inter- and intra-sexual signal and undergoes rapid variation in response to changes in mating context. Male bitterling do not modulate their courtship and aggressive behaviour in response to variation in female size, and their choice of mussel species is influenced by, and consistent with, female oviposition choice.

Habitat fragmentation can have an impact on a wide variety of biological processes including abundance, life history strategies, mating system, inbreeding and genetic diversity levels of individual species. Although fragmented populations have received much attention, ecological and genetic responses of species to fragmentation have still not been fully resolved. The current study investigated the ecological factors that may influence the demographic and genetic structure of the giant white-tailed rat (Uromys caudimaculatus) within fragmented tropical rainforests. It is the first study to examine relationships between food resources, vegetation attributes and Uromys demography in a quantitative manner. Giant white-tailed rat densities were strongly correlated with specific suites of food resources rather than forest structure or other factors linked to fragmentation (i.e. fragment size). Several demographic parameters including the density of resident adults and juvenile recruitment showed similar patterns. Although data were limited, high quality food resources appear to initiate breeding in female Uromys. Where data were sufficient, influx of juveniles was significantly related to the density of high quality food resources that had fallen in the previous three months. Thus, availability of high quality food resources appear to be more important than either vegetation structure or fragment size in influencing giant white-tailed rat demography. These results support the suggestion that a species’ response to fragmentation can be related to their specific habitat requirements and can vary in response to local ecological conditions. In contrast to demographic data, genetic data revealed a significant negative effect of habitat fragmentation on genetic diversity and effective population size in U. caudimaculatus. All three fragments showed lower levels of allelic richness, number of private alleles and expected heterozygosity compared with the unfragmented continuous rainforest site. Populations at all sites were significantly differentiated, suggesting restricted among population gene flow. The combined effects of reduced genetic diversity, lower effective population size and restricted gene flow suggest that long-term viability of small fragmented populations may be at risk, unless effective management is employed in the future. A diverse range of genetic reproductive behaviours and sex-biased dispersal patterns were evident within U. caudimaculatus populations. Genetic paternity analyses revealed that the major mating system in U. caudimaculatus appeared to be polygyny at sites P1, P3 and C1. Evidence of genetic monogamy, however, was also found in the three fragmented sites, and was the dominant mating system in the remaining low density, small fragment (P2). High variability in reproductive skew and reproductive success was also found but was less pronounced when only resident Uromys were considered. Male body condition predicted which males sired offspring, however, neither body condition nor heterozygosity levels were accurate predictors of the number of offspring assigned to individual males or females. Genetic spatial autocorrelation analyses provided evidence for increased philopatry among females at site P1, but increased philopatry among males at site P3. This suggests that male-biased dispersal occurs at site P1 and female-biased dispersal at site P3, implying that in addition to mating systems, Uromys may also be able to adjust their dispersal behaviour to suit local ecological conditions. This study highlights the importance of examining the mechanisms that underlie population-level responses to habitat fragmentation using a combined ecological and genetic approach. The ecological data suggested that habitat quality (i.e. high quality food resources) rather than habitat quantity (i.e. fragment size) was relatively more important in influencing giant white-tailed rat demographics, at least for the populations studied here . Conversely, genetic data showed strong evidence that Uromys populations were affected adversely by habitat fragmentation and that management of isolated populations may be required for long-term viability of populations within isolated rainforest fragments.