Nutritional implications of staple food crop successions in Usambara,Tanzania

Archival and ethnographic research carried out in northeastern Tanzania provides evidence of significant changes in production and consumption of staple food crops between 1850 and the present. The banana, which provided the bulk of calories and other nutrients in precolonial times, has been successively replaced by Irish potatoes, maize, and cassava in different localities. The reasons for the adoption of each of these introduced crops are explored, and their implications for human nutrition in the area are discussed.     

High frequency of extrapair copulation with low level of extrapair fertilization in the Lanyu scops owl Otus elegans botelensis

The genetic mating system is known for only a few species of owls. Most of them are genetically monogamous. The Lanyu scops owl Otus elegans botelensis breeds in high density in the forests of Lanyu (Orchid Island), southeast of Taiwan. Because extra‐pair copulations (EPCs) have frequently been observed, we suspected a high degree of extra‐pair fertilizations (EPFs). Through intensive field observations we quantified both within‐pair and extra‐pair copulations of this owl, and used a set of microsatellite loci to assign the parentage of 200 offspring from 108 families collected between 1999 and 2004. Among copulations for which we could identify both participants, 19.77% were EPC. However, no EPC was observed in the period just before egg laying. We found only two cases of parentage mismatch among 108 broods. The first case was most likely a case of brood usurpation, which would be the first case reported in the Strigidae. The second case was an EPF resulting in one offspring. Our study found that parentage mismatch in the Lanyu scops owls to be extremely low, therefore reproductive success can be estimated accurately by simply counting chicks in nests.     

High frequency of extrapair copulation with low level of extrapair fertilization in the Lanyu scops owl Otus elegans botelensis

The genetic mating system is known for only a few species of owls. Most of them are genetically monogamous. The Lanyu scops owl Otus elegans botelensis breeds in high density in the forests of Lanyu (Orchid Island), southeast of Taiwan. Because extra-pair copulations (EPCs) have frequently been observed, we suspected a high degree of extra-pair fertilizations (EPFs). Through intensive field observations we quantified both within-pair and extra-pair copulations of this owl, and used a set of microsatellite loci to assign the parentage of 200 offspring from 108 families collected between 1999 and 2004. Among copulations for which we could identify both participants, 19.77% were EPC. However, no EPC was observed in the period just before egg laying. We found only two cases of parentage mismatch among 108 broods. The first case was most likely a case of brood usurpation, which would be the first case reported in the Strigidae. The second case was an EPF resulting in one offspring. Our study found that parentage mismatch in the Lanyu scops owls to be extremely low, therefore reproductive success can be estimated accurately by simply counting chicks in nests.     

Power to detect trends in ecological indicators in the East Usambara Mountains, Tanzania

We evaluated the statistical power of monitoring protocols to detect, over a 10‐year period, trends in indices of abundance of primates, hornbills and forest interior dung beetles and growth rates of epiphytic ferns in the Amani Nature Reserve, in the East Usambara Mountains, Tanzania. Local technicians are responsible for the day‐to‐day gathering of data. The existing monitoring protocols for blue monkey, silver‐cheeked hornbills, trumpeter hornbills, forest interior dung beetles and Asplenium nidus have sufficient statistical power (>0.80) to detect trends of 65% or less over a 10‐year period. Monitoring protocols for black and white colobus and Asplenium holstii have lower statistical power (<0.80). We therefore conclude that the majority of monitoring protocols of the East Usambara Ecological Monitoring Project have the capacity both logistically and statistically to detect long‐term trends in important functional groups in the East Usambara Mountains.     

Seasonal patterns of rodents, fleas and plague status in the Western Usambara Mountains, Tanzania

Field and commensal rodents were live-trapped at three villages in an active focus of plague (Yersinia pseudotuberculosis pestis) in Lushoto District, Western Usambara Mountains, Tanga Region, Tanzania, from December 1983 to November 1984. Their flea ectoparasites were collected, identified and counted. The rodent carcasses were serologically examined for specific plague antibodies and antigens, and bacteriologically examined for bipolar staining bacilli. A total of 1758 traps were set during the 12-month period and 924 animals were caught. From these, 1037 fleas were collected. Rattus rattus (L.), Praomys natalensis (Smith) and Lophuromys flavopunctatus Thomas comprised the largest proportions of the rodent population, while Dinopsyllus lypusus Jordan & Rothschild, Ctenophthalmus calceatus Waterston and Xenopsylla brasiliensis (Baker) were the dominant flea species. Rodents were most abundantly trapped during December and January. Flea indices were highest from December to May. Human plague was most active from November to March. Rodents contained plague antibodies every month except May and July, with a peak in September. Plague antigens and bipolar bacilli were detected in rodent organs during January-April. From the product of abundance and infection rate, the most prevalent rodent hosts of plague appeared to be R. rattus, Otomys angoniensis Wroughton, P. natalensis and Pelomys fallax (Peters). Continuous integrated control of rodents and fleas was recommended, reinforced by quarantine and maintenance of a surveillance service for clinical detection, diagnosis and treatment of patients in the plague endemic area.     

Predicting fluctuations of reintroduced ibex populations: the importance of density dependence, environmental stochasticity and uncertain population estimates

1. Development of population projections requires estimates of observation error, parameters characterizing expected dynamics such as the specific population growth rate and the form of density regulation, the influence of stochastic factors on population dynamics, and quantification of the uncertainty in the parameter estimates. 2. Here we construct a Population Prediction Interval (PPI) based on Bayesian state space modelling of future population growth of 28 reintroduced ibex populations in Switzerland that have been censused for up to 68 years. Our aim is to examine whether the interpopulation variation in the precision of the population projections is related to differences in the parameters characterizing the expected dynamics, in the effects of environmental stochasticity, in the magnitude of uncertainty in the population parameters, or in the observation error. 3. The error in the population censuses was small. The median coefficient of variation in the estimates across populations was 5.1%. 4. Significant density regulation was present in 53.6% of the populations, but was in general weak. 5. The width of the PPI calculated for a period of 5 years showed large variation among populations, and was explained by differences in the impact of environmental stochasticity on population dynamics. 6. In spite of the high accuracy in population estimates, the uncertainty in the parameter estimates was still large. This uncertainty affected the precision in the population predictions, but it decreased with increasing length of study period, mainly due to higher precision in the estimates of the environmental variance in the longer time-series. 7. These analyses reveal that predictions of future population fluctuations of weakly density-regulated populations such as the ibex often become uncertain. Credible population predictions require that this uncertainty is properly quantified.     

Food limitation of population density in the orb-wed spider,Nephila clavata

Field studies were conducted to clarify whether variation in food availability among habitats influences population density, and whether population density has a negative effect on foraging success in the orb-web spider, Nephila clavata. Lifetime food consumption per individual (i.e., foraging success) strongly correlated with mean body size of adult females and mean fecundity in populations. Also, there was a positive correlation between foraging success and population density. Since foraging success reflected potential prey availability in the habitat, food resource appeared to be a limiting factor for populations in this spider. Mean fecundity per individual correlated with population density of the following year, suggesting that decreased reproduction is a major component of food limitation on population density. Consistent defferences in mean body size between particular sites were observed over years, while such difference was less obvious in density. Thus, ranking of food abundance among habitats seems to be predictable between years. A field experiment revealed that an artificial increase in population density had no negative effect on the feeding rate of individuals, suggesting that intraspecific competition for food is not important in this species.     

Species richness and endemism in the Usambara mountain forests, Tanzania

The East Usambara Mountain forests constitute what is probably one of the richest biological communities in Africa in terms of plant and animal species numbers and endemic taxa. This review presents brief accounts of the flora and of three invertebrate and four vertebrate groups and shows the percentage endemic taxa to vary from 2% (mammals) to 95% (millipedes) as a proportion of the true forest species.
Notes are given on the geology, soils, climate and present land use of the Usambaras. Biological richness is considered to be due to long periods of isolation and geological stability coupled with periods of species immigration during times of re-establishment of a continuous forest cover. The nature of the endemic elements is briefly discussed.
Evidence is given to show that the forests are subject to increasing pressure from legal and illegal encroachment due to agriculture (tea, cardamon, subsistence) and forestry timber operations. Air photograph analysis shows a forest decrease of some 50% in the vicinity of Amani from 1954 to 1976.
The low conservation status of most forest reserves and the lack of detailed knowledge on the distribution, status and biology of the endemic species means present conservation efforts are poor and haphazard. This review calls for greatly increased research inputs and a complete halt to all exploitation of natural forest areas until a long term conservation land use plan can be implemented.     

Cycles, stochasticity and density dependence in pink salmon population dynamics

Complex dynamics of animal populations often involve deterministic and stochastic components. A fascinating example is the variation in magnitude of 2-year cycles in abundances of pink salmon (Oncorhynchus gorbuscha) stocks along the North Pacific rim. Pink salmon have a 2-year anadromous and semelparous life cycle, resulting in odd- and even-year lineages that occupy the same habitats but are reproductively isolated in time. One lineage is often much more abundant than the other in a given river, and there are phase switches in dominance between odd- and even-year lines. In some regions, the weak line is absent and in others both lines are abundant. Our analysis of 33 stocks indicates that these patterns probably result from stochastic perturbations of damped oscillations owing to density-dependent mortality caused by interactions between lineages. Possible mechanisms are cannibalism, disease transmission, food depletion and habitat degradation by which one lineage affects the other, although no mechanism has been well-studied. Our results provide comprehensive empirical estimates of lagged density-dependent mortality in salmon populations and suggest that a combination of stochasticity and density dependence drives cyclical dynamics of pink salmon stocks.     

Structure of population,grouping patterns and density of forest elephants in north-west Congo

The structure of the population of forest elephants visiting a clearing in north-west Congo was studied over 8 months. Out of 3314 sightings, 629 elephants were identified (including 64%, of adults). The sex ratio was about 1:1. The number of offspring per female was 1.12. Solitary elephants (91.4%, of males) made up 35% of the population. Of females, 93.6% were grouped. Groups (mean size 3.5) included females and offspring (3.4), males and females (5.0), or males only (2.3). The return rate of elephants at the clearing suggested that up to 1900 individuals have visited the clearing. This confirms that elephant densities are especially high in north Congo.     

贵阳市景观类型与人口密度相关分析

以CBERS-1为数据源,获取贵阳市景观数据,通过简单相关和偏相关分析,从定量角度阐明人口密度和景观类型之间的相关关系和相关程度。结果表明,简单相关分析和偏相关分析的差别很小,不能影响变量之间的相关关系;相关分析中,只有居民点及建设景观与人口密度为正相关,且相关关系不显著,其他均为负相关,其中农田景观、林地景观、草地景观为显著相关,石漠化景观相关性不显著,水域景观和园地景观可视为无相关性;人类活动对自然界景观格局的影响虽然广泛而深刻,但以人类干扰景观为主,人口密度对景观格局不存在决定性的作用。     

Microphytoplankton of the Pitchavaram mangals,southeast coast of India: species composition and population density

Species richness of phytoplankton of the Pitchavaram mangals was high. There were 82 species constituted by 67 species of diatoms, 12 species of dinoflagellates and 3 species of bluegreen algae. The diatoms formed the bulk with 72% followed by the dinoflagellates with 15%, in which there were autochthonous (temporary and permanent) and allochthonous forms. Phytoplankton population density exhibited a wide seasonal fluctuation with the minimum during monsoon and the maximum during summer, suggesting the possible differential influence of various environmental factors.     

棉田绿盲蝽种群密度的调查方法

本文比较研究了棉田绿盲蝽Apolygus lucorum(Meyer-Dür)种群的调查方法。全株调查法中,目测法调查到的绿盲蝽种群密度最高,显著高于扫网法和盆拍法。局部调查法发现,蕾上的绿盲蝽种群数量显著高于叶片和花上;蕾上种群数量与整株密度之间呈显著正相关关系(y=1.18 x+3.69)。间接调查法表明:在苗期和蕾期,叶片受害等级和绿盲蝽种群密度之间呈显著正相关关系(苗期:y=25.28 x+8.20;蕾期:y=43.99 x+27.58)。     

Effects of poaching on bull mating success in a free ranging African elephant (Loxodonta africana) population in Tarangire National Park, Tanzania

Poaching and habitat encroachment for human settlement are the two major factors that caused contraction of elephant populations in Africa. While the effects of poaching on many aspects of elephant social systems have been studied, the impacts on mating patterns are not yet understood and such information is still lacking in most African countries. In this study, we used elephant specific-microsatellite DNA to generate genotypes from 86 elephant samples (84 fresh faeces and two tissue samples) from Tarangire National Park (TNP), Tanzania to assess the mating success of individual males. We also tested whether the oldest bulls are more likely to sire most of the offspring in a severely poached population. Genetic paternity analysis was compared to behavioural observations of matings collected over a 3-year period (1998–2001) to determine the success of bull mating strategy. The genotypes of 26 infants, their known mothers and 10 out of 43 potential breeding bulls in TNP were used to assign 31% of the offspring at 80% confidence level to their potential fathers with simulation assuming that 23% (10/43) of the breeding males were sampled. Mating success of individual bull based on both behavioural and genetic data showed that the oldest remaining bulls performed most of the matings and fathered the majority of infants. We speculate that the lifetime fitness of bulls that have survived poaching may be elevated because their period of dominance increases.     

Lion density and population structure in the Selous Game Reserve: evaluation of hunting quotas and offtake

In 1992, tourist hunting in the Selous Game Reserve generated 1.28 million dollars for the Tanzanian government, of which 0·96 million dollars were returned to wildlife conservation. Lions ( Panthera leo ) are one of three critical species for tourist hunting, consistently generating 12%–13% of hunting revenue from 1988 to 1992. Because of their ecological and economic importance (and intrinsic value), it is important that lion quotas be set so that offtake is sustainable. The population density of lions in Selous ranges from 0·08 to 0·13 adults km⁻², comparable to unhunted ecosystems. The adult sex ratio (36–41% male) and the ratio of cubs to adults (29% cubs) are similar to those of unhunted populations. The ratio of lions to hyaenas is lower in heavily hunted areas (0·17 lions/hyena) than in unhunted areas (0·43 lions/hyena). Hunting levels between 1989 and 1994 took 2·7–4·3% of adult males annually, which is sustainable. The current quota is 10–16% of the adult male population, which exceeds natural mortality rates for male lions. To remain stable if the quota was filled, the population would have to compensate via increased fecundity, increased juvenile survival, or an altered sex‐ratio. Compensation occurs in Selous by producing (or raising) more male than female cubs (66–81% of juveniles are male). Only 28% of the Selous quota was filled in 1992. The percentage of quota filled (both in Selous and nationwide) has dropped since 1988 as quotas have increased. The current intensity of lion hunting in Selous is sustainable, but the quota cannot be filled sustainably.     

Abundance and distribution of mammals in Katavi National Park, Tanzania

Ground transects were used to determine densities of 24 larger mammals in Katavi National Park. The Park consists of miombo woodland habitat and two seasonal lakes. Mammalian biomass was extremely high due primarily to large numbers of buffalo. The highest mammal densities were found around Lake Chada to the south-east of the Park. Contrary to earlier reports, species' densities did not differ significantly between dry, wet and intermediate seasons, suggesting that, aside from elephant and warthog, mammals did not enter or leave the Park in large numbers. Similarly, aside from zebra and waterbuck, sightings of species in different vegetation types did not change markedly between seasons. Thus, seasonal lakes in Katavi National Park support very high local concentrations rather than acting as dry season refuges for mammals outside the Park.