Stephen Blake - Academia.edu (original) (raw)
Papers by Stephen Blake
by Thomas Breuer, Alasdair R Harris, Stephen Blake, Charles-Albert Petre, Sandra Tranquilli, Fidèle Amsini, Tim Davenport, Colin A Chapman, Takeshi Furuichi, Kouame Paul Ngoran, Sebastien Regnaut, Cletus Balangtaa, Manasseh Eno-Nku, and Rebecca Chancellor
PLoS ONE
Numerous protected areas (PAs) have been created in Africa to safeguard wildlife and other natura... more Numerous protected areas (PAs) have been created in Africa to safeguard wildlife and other natural resources. However, significant threats from anthropogenic activities and decline of wildlife populations persist, while conservation efforts in most PAs are still minimal. We assessed the impact level of the most common threats to wildlife within PAs in tropical Africa and the relationship of conservation activities with threat impact level. We collated data on 98 PAs with tropical forest cover from 15 countries across West, Central and East Africa. For this, we assembled information about local threats as well as conservation activities from published and unpublished literature, and questionnaires sent to long-term field workers. We constructed general linear models to test the significance of specific conservation activities in relation to the threat impact level. Subsistence and commercial hunting were identified as the most common direct threats to wildlife and found to be most pr...
African Journal of Ecology, 1995
PLoS Biology, 2007
Debate over repealing the ivory trade ban dominates conferences of the Convention on Internationa... more Debate over repealing the ivory trade ban dominates conferences of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). Resolving this controversy requires accurate estimates of elephant population trends and rates of illegal killing. Most African savannah elephant populations are well known; however, the status of forest elephants, perhaps a distinct species, in the vast Congo Basin is unclear. We assessed population status and incidence of poaching from line-transect and reconnaissance surveys conducted on foot in sites throughout the Congo Basin. Results indicate that the abundance and range of forest elephants are threatened from poaching that is most intense close to roads. The probability of elephant presence increased with distance to roads, whereas that of human signs declined. At all distances from roads, the probability of elephant occurrence was always higher inside, compared to outside, protected areas, whereas that of humans was always lower. Inside protected areas, forest elephant density was correlated with the size of remote forest core, but not with size of protected area. Forest elephants must be prioritised in elephant management planning at the continental scale.
Plan d'action régional pour la conservation des chimpanzés et des gorilles en Afrique Centrale 1 ... more Plan d'action régional pour la conservation des chimpanzés et des gorilles en Afrique Centrale 1 Plan d'action régional pour la conservation des chimpanzés et des gorilles en Afrique Centrale (Pan troglodytes troglodytes et Gorilla gorilla gorilla) Compilé et édité par Jeune mâle chimpanzé du triangle de Goualougo, parc national de Nouabalé-Ndoki, République du Congo; ces chimpanzés montraient des comportements naïfs quand observés pour la première fois par les chercheurs suggérant qu'ils avaient eu peu de contacts avec des humains auparavant. © Nick Nichols, NGS Un mâle adulte gorille possède un dos argenté et une crête rouge qui est la caractéristique des gorilles de plaine d'Afrique Centrale.
Journal of Animal Ecology, 2011
1. Large data sets containing precise movement data from free-roaming animals are now becoming co... more 1. Large data sets containing precise movement data from free-roaming animals are now becoming commonplace. One means of analysing individual movement data is through discrete, random walk-based models. 2. Random walk models are easily modified to incorporate common features of animal movement, and the ways that these modifications affect the scaling of net displacement are well studied. Recently, ecologists have begun to explore more complex statistical models with multiple latent states, each of which are characterized by a distribution of step lengths and have their own unimodal distribution of turning angles centred on one type of turn (e.g. reversals).
Journal of Animal Ecology, 2013
1. Seasonal migration has evolved in many taxa as a response to predictable spatial and temporal ... more 1. Seasonal migration has evolved in many taxa as a response to predictable spatial and temporal variation in the environment. Individual traits, physiology and social state interact with environmental factors to increase the complexity of migratory systems. Despite a huge body of research, the ultimate causes of migration remain unclear. 2. A relatively simple, tractable systemgiant tortoises on Santa Cruz Island, Galapagos, was studied to elucidate the roles of environmental variation and individual traits in a partial migratory system. Specifically, we asked: (i) do Galapagos tortoises undergo long-distance seasonal migrations? (ii) is tortoise migration ultimately driven by gradients in forage quality or temperature; and (iii) how do sex and body size influence migration patterns? 3. We recorded the daily locations of 17 GPS-tagged tortoises and walked a monthly survey along the altitudinal gradient to characterize the movements and distribution of tortoises of different sizes and sexes. Monthly temperature and rainfall data were obtained from weather stations deployed at various altitudes, and the Normalized Difference Vegetation Index was used as a proxy for forage quality. 4. Analyses using net displacement or daily movement characteristics did not agree on assigning individuals as either migratory or non-migratory; however, both methods suggested that some individuals were migratory. Adult tortoises of both sexes move up and down an altitudinal gradient in response to changes in vegetation dynamics, not temperature. The largest tagged individuals all moved, whereas only some mid-sized individuals moved, and the smallest individuals never left lowland areas. The timing of movements varied with body size: large individuals moved upward (as lowland forage quality declined) earlier in the year than did mid-sized individuals, while the timing of downward movements was unrelated to body size and occurred as lowland vegetation productivity peaked. 5. Giant tortoises are unlikely candidates for forage-driven migration as they are well buffered against environmental fluctuations by large body size and a slow metabolism. Notably the largest, and presumably most dominant, individuals were most likely to migrate. This characteristic and the lack of sex-based differences in movement behaviour distinguish Galapagos tortoise movement from previously described partial migratory systems.
Conservation Biology, 2004
Biotropica, 2009
The abundance of large vertebrates is rapidly declining, particularly in the tropics where over-h... more The abundance of large vertebrates is rapidly declining, particularly in the tropics where over-hunting has left many forests structurally intact but devoid of large animals. An urgent question then, is whether these 'empty' forests can sustain their biodiversity without large vertebrates. Here we examine the rol eo f forest elephant (Loxodonta africana cyclotis) seed dispersal in maintaining the community structure
This action plan represents a consensus of the world's leading experts on the priority areas... more This action plan represents a consensus of the world's leading experts on the priority areas and priority actions needed for preserving wild chimpanzee and gorilla populations in western equatorial Africa. The results were generated at a workshop held in Brazzaville, Republic of Congo ...
African Journal of Ecology, 2001
Few data exist on the ranging behaviour of forest elephants. A feasibility study on the use of GP... more Few data exist on the ranging behaviour of forest elephants. A feasibility study on the use of GPS telemetry as a tool to study ranging, seasonal movements and distribution was implemented in the Dzanga-Sangha and Nouabalé-Ndoki National Parks Complex of Central African ...
by Thomas Breuer, Alasdair R Harris, Stephen Blake, Charles-Albert Petre, Sandra Tranquilli, Fidèle Amsini, Tim Davenport, Colin A Chapman, Takeshi Furuichi, Kouame Paul Ngoran, Sebastien Regnaut, Cletus Balangtaa, Manasseh Eno-Nku, and Rebecca Chancellor
PLoS ONE
Numerous protected areas (PAs) have been created in Africa to safeguard wildlife and other natura... more Numerous protected areas (PAs) have been created in Africa to safeguard wildlife and other natural resources. However, significant threats from anthropogenic activities and decline of wildlife populations persist, while conservation efforts in most PAs are still minimal. We assessed the impact level of the most common threats to wildlife within PAs in tropical Africa and the relationship of conservation activities with threat impact level. We collated data on 98 PAs with tropical forest cover from 15 countries across West, Central and East Africa. For this, we assembled information about local threats as well as conservation activities from published and unpublished literature, and questionnaires sent to long-term field workers. We constructed general linear models to test the significance of specific conservation activities in relation to the threat impact level. Subsistence and commercial hunting were identified as the most common direct threats to wildlife and found to be most pr...
African Journal of Ecology, 1995
PLoS Biology, 2007
Debate over repealing the ivory trade ban dominates conferences of the Convention on Internationa... more Debate over repealing the ivory trade ban dominates conferences of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). Resolving this controversy requires accurate estimates of elephant population trends and rates of illegal killing. Most African savannah elephant populations are well known; however, the status of forest elephants, perhaps a distinct species, in the vast Congo Basin is unclear. We assessed population status and incidence of poaching from line-transect and reconnaissance surveys conducted on foot in sites throughout the Congo Basin. Results indicate that the abundance and range of forest elephants are threatened from poaching that is most intense close to roads. The probability of elephant presence increased with distance to roads, whereas that of human signs declined. At all distances from roads, the probability of elephant occurrence was always higher inside, compared to outside, protected areas, whereas that of humans was always lower. Inside protected areas, forest elephant density was correlated with the size of remote forest core, but not with size of protected area. Forest elephants must be prioritised in elephant management planning at the continental scale.
Plan d'action régional pour la conservation des chimpanzés et des gorilles en Afrique Centrale 1 ... more Plan d'action régional pour la conservation des chimpanzés et des gorilles en Afrique Centrale 1 Plan d'action régional pour la conservation des chimpanzés et des gorilles en Afrique Centrale (Pan troglodytes troglodytes et Gorilla gorilla gorilla) Compilé et édité par Jeune mâle chimpanzé du triangle de Goualougo, parc national de Nouabalé-Ndoki, République du Congo; ces chimpanzés montraient des comportements naïfs quand observés pour la première fois par les chercheurs suggérant qu'ils avaient eu peu de contacts avec des humains auparavant. © Nick Nichols, NGS Un mâle adulte gorille possède un dos argenté et une crête rouge qui est la caractéristique des gorilles de plaine d'Afrique Centrale.
Journal of Animal Ecology, 2011
1. Large data sets containing precise movement data from free-roaming animals are now becoming co... more 1. Large data sets containing precise movement data from free-roaming animals are now becoming commonplace. One means of analysing individual movement data is through discrete, random walk-based models. 2. Random walk models are easily modified to incorporate common features of animal movement, and the ways that these modifications affect the scaling of net displacement are well studied. Recently, ecologists have begun to explore more complex statistical models with multiple latent states, each of which are characterized by a distribution of step lengths and have their own unimodal distribution of turning angles centred on one type of turn (e.g. reversals).
Journal of Animal Ecology, 2013
1. Seasonal migration has evolved in many taxa as a response to predictable spatial and temporal ... more 1. Seasonal migration has evolved in many taxa as a response to predictable spatial and temporal variation in the environment. Individual traits, physiology and social state interact with environmental factors to increase the complexity of migratory systems. Despite a huge body of research, the ultimate causes of migration remain unclear. 2. A relatively simple, tractable systemgiant tortoises on Santa Cruz Island, Galapagos, was studied to elucidate the roles of environmental variation and individual traits in a partial migratory system. Specifically, we asked: (i) do Galapagos tortoises undergo long-distance seasonal migrations? (ii) is tortoise migration ultimately driven by gradients in forage quality or temperature; and (iii) how do sex and body size influence migration patterns? 3. We recorded the daily locations of 17 GPS-tagged tortoises and walked a monthly survey along the altitudinal gradient to characterize the movements and distribution of tortoises of different sizes and sexes. Monthly temperature and rainfall data were obtained from weather stations deployed at various altitudes, and the Normalized Difference Vegetation Index was used as a proxy for forage quality. 4. Analyses using net displacement or daily movement characteristics did not agree on assigning individuals as either migratory or non-migratory; however, both methods suggested that some individuals were migratory. Adult tortoises of both sexes move up and down an altitudinal gradient in response to changes in vegetation dynamics, not temperature. The largest tagged individuals all moved, whereas only some mid-sized individuals moved, and the smallest individuals never left lowland areas. The timing of movements varied with body size: large individuals moved upward (as lowland forage quality declined) earlier in the year than did mid-sized individuals, while the timing of downward movements was unrelated to body size and occurred as lowland vegetation productivity peaked. 5. Giant tortoises are unlikely candidates for forage-driven migration as they are well buffered against environmental fluctuations by large body size and a slow metabolism. Notably the largest, and presumably most dominant, individuals were most likely to migrate. This characteristic and the lack of sex-based differences in movement behaviour distinguish Galapagos tortoise movement from previously described partial migratory systems.
Conservation Biology, 2004
Biotropica, 2009
The abundance of large vertebrates is rapidly declining, particularly in the tropics where over-h... more The abundance of large vertebrates is rapidly declining, particularly in the tropics where over-hunting has left many forests structurally intact but devoid of large animals. An urgent question then, is whether these 'empty' forests can sustain their biodiversity without large vertebrates. Here we examine the rol eo f forest elephant (Loxodonta africana cyclotis) seed dispersal in maintaining the community structure
This action plan represents a consensus of the world's leading experts on the priority areas... more This action plan represents a consensus of the world's leading experts on the priority areas and priority actions needed for preserving wild chimpanzee and gorilla populations in western equatorial Africa. The results were generated at a workshop held in Brazzaville, Republic of Congo ...
African Journal of Ecology, 2001
Few data exist on the ranging behaviour of forest elephants. A feasibility study on the use of GP... more Few data exist on the ranging behaviour of forest elephants. A feasibility study on the use of GPS telemetry as a tool to study ranging, seasonal movements and distribution was implemented in the Dzanga-Sangha and Nouabalé-Ndoki National Parks Complex of Central African ...