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1.
The population of puku, Kobus vardonii, at Lake Rukwa, one of only two in Tanzania, is poorly known. A multi‐species dry season game count carried out in Rukwa Game Reserve (RGR) in 2004 estimated a population size of 1729, but was associated with a high margin of error [coefficient of variation (CV) 0.88]. To increase the precision for the local puku population estimate, we conducted a zig‐zag line transect survey restricted only to areas occupied by puku in the dry season of 2006. This survey technique produced an estimate of 776 individuals and the CV was considerably reduced to 0.29. Puku herd size was comparable with the studies carried out in the Kilombero valley, Tanzania and in Kasanka National Park, Zambia, thus broadly confirming the herding ecology of this species. We found that pukus were restricted to the central parts of the floodplains, suggesting an avoidance of habitats used by pastoralists at the edge of RGR. Compared with the estimates of the puku population made in the 1980s, the puku population has declined. We recommend regular monitoring and enforcement of the current management plan to conserve the local puku population.  相似文献   

2.
Within the Kilombero Game Controlled Area (KGCA) of Tanzania, protection is offered to large mammal populations by trophy hunting concessions that maintain natural habitat through the prevention of extensive human encroachment. The opinions of local communities to wildlife management operations such as trophy hunting play an important role in their long‐term viability. This study addresses the influence of socio‐demographic factors on the opinions of local communities to trophy hunting in areas that are not part of community‐based management projects, which is where most research of this type has previously been conducted. Semi‐structured questionnaires were conducted in 24 villages within the Kilombero Valley (fifteen interviews per village) in August–December 2007. The extent to which socio‐demographic factors including location (e.g. village of residence) and individual respondent characteristics (e.g. gender and age) influenced the respondents’ opinions was analysed. Of these socio‐demographic factors, all, except age and district of residence, were found to influence the opinions of local residents. Socio‐demographic factors play an important role in determining local communities’ attitudes towards trophy hunting, and this must be taken into account during the design and assessment of wildlife management conservation strategies, both locally in the KGCA and in similar national and international initiatives.  相似文献   

3.
We assessed dung and track counts for indexing brocket deer abundance in seasonal habitats on a ranch where hunting is not practiced in the Bolivian lowlands. Surveys were replicated along four 10-km trails (totaling 180 km in the wet season and 90 km in the dry season) through four semideciduous forest habitats. Dung pellets and tracks were identified as belonging to Mazama gouazoubira or M. americana by size and shape. Pellet groups lasted more than 1 month during the dry season, but decayed within 1–2 weeks in the wet season. Mean density estimates based on dung counts varied widely between seasons for gray brockets (from 6.77±4.0 to 30.57±23.5 ind/km2; mean±SD) but not for reds (from 3.52±4.6 to 6.98±7.2 ind/km2). These values were probably too high due to underestimation of daily deposition rate, and were reduced during the wet season because of dung decay. We found consistently more dung in the dry season and more tracks in the wet season. Sightings of red brockets were too few for line-transect analysis (n=6), but those of gray brockets (n=42) produced an overall estimate of 5.6 ind/km2 (95% CI=3.5–9.0 ind/km2). Different estimates indicated that gray brockets were more abundant than reds in all situations, except perhaps in the riverine forest. Environmental factors affected these indices of abundance differently, and while we recommend the use of dung counts in dry-season scenarios, we think that index reliability should be assessed locally before conducting population comparisons.  相似文献   

4.
The breeding cycle, recruitment, population dynamics, growth and production ofScrobicularia plana were studied at one station in the Bidasoa estuary (SE of the Biscay Bay, Spain) during a period of 3 or 4 years. To complete this study, the reproduction for a period of 1 year was analysed at two other sites of the estuary. At none of the stations important differences in spawning activity were observed between the different years. The animals reproduced for the first time when they reached the age of two years. The histological data and the recruitment analysis showed only one spawning period between June and mid-September, with a peak in July-August. This breeding pattern differs from those shown by other southern European populations. The recruitment of spat (0.25–0.50 mm) occurred from June–July to October–December in different years. The population showed different annual patterns of density and population structure, depending on recruitment success. Growth was most rapid in spring and summer. The bivalves reached a mean length of 21.8 mm at the age of approximately 16 months; in the following year they grew to 30 mm. The growth during the life span fitted the theoretical growth equation of Von Bertalanffy. Annual production was in the range of 59.0–83.4 g AFDW m–2 year–1. The P/B ratios of the population varied between 0.84 and 1.48 (1.06 ± 1.36; ¯x ± 95% C.I.).  相似文献   

5.
Gracilaria changii, recorded from Malaysia and Thailand, is one of the more abundant agarophytic seaweeds found in Malaysia. A wild population of Gracilaria changii growing in mangroves was monitored for seasonal variation in agar content and gel strength as well as spore production. Agar yield and gel strength ranged from 12 to 25% dry weight and 294 to 563 g cm–2, respectively, over a 15-month period. Gel strength but not yield was positively correlated with amount of rainfall. Cystocarps were observed throughout the study, but use of sporetraps showed that spore release peaked around July–August and January–February after the two monsoon periods.Mariculture of Gracilaria changii in shallow ponds in the mangroves, in an irrrigation canal and in a shrimp farm pond was conducted. Average growth rate of cuttings tied to monofilament lines was 3.3 ± 1.7% d–1, 8.4 ± 1.8% d–1 and 3.6 ± 1.6% d–1 respectively. Cuttings were lost to siltation, wave action, predation and heavy epiphytisation.These studies show that Gracilaria changii has potential commercial application in the agar industry.  相似文献   

6.
Litterfall from a Melaleuca forest was investigated as part of chemical cycling studies on the Magela Creek floodplain in tropical, northern Australia. The forest contained two species of tree, Melaleuca cajaputi and Melaleuca viridiflora, with a combined average density of 294 trees ha–1. The M. viridiflora trees had diameter breast height measurements ranging from 11.8 to 62.0 cm, median class 25.1–30.0cm and a mean value of 29.2±1.0 cm, compared to 13.0 to 66.3 cm, 30.1–35.0cm and 33.5±1.0cm for M. cajaputi trees. A regression model between tree height, diameter breast height and fresh weight was determined and used to calculate average tree weights of 775±1.6kg for M. viridiflora and 1009±1.6kg for M. cajaputi, and a total above-ground fresh weight of 263±0.3t ha–1. The weight of litter recorded each month on the ground beneath the tree canopy ranged from 582±103 to 2176±376 g m–2 with a monthly mean value of 1105±51 g m–2. The coefficient of variation of 52% on this mean indicates the large spatial and temporal variability in litter distribution over the study site. This variability was greatly affected by the pattern of water flow and litter transport during the Wet season. Litterfall from the trees was evaluated using two techniques - nets and trays. The results from these techniques were not significantly different with annual litterfall collected in the nets being 705 ± 25 g m–2 and in the trays 716±49 g m–2. The maximum monthly amount of litterfall, 108 ±55g m–2, occurred during the Dry season months of June–July. Leaf material comprised 70% of the total annual weight of litter, 480±29 g m–2 in the nets and 495 ± 21 g m–2 in the trays. The tree density and weight of litter suggest that the Melaleuca forests are highly productive and contribute a large amount of material to the detrital/debris turnover cycle on the floodplain.  相似文献   

7.
Very little information is available on the current status of drill populations in Cameroon. We report on drill group sizes and status in Bakossiland, a mountainous area spanning 2000 km2 in the Littoral and South West Provinces of southwestern Cameroon. Between 1970 and 2002 direct visual counts of drill groups (n = 105) yielded group size estimates ranging from 5 to 400 (mean ± S.E.M.; 93.1 ± 8.4). We encountered solitary adult male drills on 8 occasions. Groups were at all elevations (150–2000 m) in 5 habitat types: lowland, premontane, submontane and montane forests and montane savannah at 2000 m). Group sizes did not vary with respect to elevation, habitat type or season (wet and dry mo). However, over the past decade drills have been virtually hunted out of the Mwenzekong Mountains (Banyang Mbo Wildlife Sanctuary), and they are greatly reduced in the southern Bakossi forests of Mwendolengo, Edib Hills and Mungo River. The species became extinct in the Loum Forest Reserve in the late 1970s, and until recently was thought to have become extinct on Mount Mwanenguba. Since 1994 on Mount Kupe, the drill population has begun to recover, largely due to protection afforded by the Bakossi traditional chiefs. Traditional powers and values are still influential in the region. A new national park—Bakossi Mountains National Park— and associated Protected Areas are currently under gazettment. We discuss the effectiveness of conservation strategies in relation to the survival of drills in the area.  相似文献   

8.
Summary The nitrogen fixation rate in a 4-year-old stand of the woody legumeLeucaena leucocephala (Lam.) de Wit. was estimated in the field at a rather dry site in Tanzania by use of an acetylene reduction technique. The diurnal mean value during April–May was 35 nmol C2H4 mg–1 (dry weight) nodules h–1, with a variation between 22±8 and 48±12 nmol C2H4 mg–1 (dry weight) nodules h–1 in early morning and at midday, respectively. The nodule biomass was determined by auger sampling to be 51±16 kg (dry weight) ha–1. Most of the nodules were found at the 10–30 cm soil depth level. A rough calculation of the amount of nitrogen fixed annually arrived at 110±30 kg ha–1. The results give strong support for the use ofL. leucocephala for soil enrichment in less humid areas of tropical Africa.  相似文献   

9.
A study of the local population of the variegated grasshopper, Z. variegatus on the Nsukka Plateau, Nigeria, has shown that there are two populations, the dry season and the wet season populations, whose life-histories overlap.The average span of life, from nymph to adult of the individuals of either population is 9–10 months, while development from nymph to reproductive maturity in either form is 4–5 months. For the dry season population, nymphs appear in October, young adults by March–April, and by August the last remnants of this population die out. The wet season individuals appear first as nymphs by about February, as young adults by June, and die out by about December. In general, egg pods remain in the soil for 5–6 months (April–October), and for 4–5 months (October–February) for the dry season and wet season individuals respectively, before hatching. The shorter period spent in the soil by the eggs of the wet season individuals appears to be due to the fact of delay of oviposition in the mature females by the extreme wetness of the soil when reproductive maturity is attained.In the laboratory, attempts to mate reproductively mature and copulating adults from either seasonal population with each other, were not successful.The phenology of the dry season population is the same, whether reared in the laboratory or in the field.The growth characteristics of these grasshoppers conform to Dyar's rule. However, while growth as indicated by increases in mean body length is linear, growth as indicated by weight measurements shows a two-phase relationship, the divergence appearing at the IV instar.
Résumé Une étude de la population locale de Z. variegatus sur le Plateau Nsukka au Nigeria, a montré qu'il y a en fait coexistence de deux populations distinctes, dont les cycles biologiques se chevauchent, l'une correspondant à la saison sèche et l'autre à la saison humide.La longévité moyenne des individus (vie larvaire + vie imaginale) dans l'une ou l'autre de ces populations est de 9 à 10 mois, le développement, depuis la larve jusqu'à la maturité sexuelle, étant de 4 à 5 mois. Pour la population de la saison sèche, les larves apparaissent en octobre, les jeunes adultes en mars–avril, et les derniers survivants s'observent jusqu'en août. Les larves des individus de la saison humide apparaissent courant février, leurs jeunes adultes en juin, et la population s'éteint en décembre.En général les coques ovigères n'éclosent qu'après un séjour dans le sol de 5 à 6 mois (avril à octobre) pour la population de la saison sèche, et de 4 à 5 mois (octobre à février) pour la population de la saison humide. Le fait que le temps d'incubations dans le sol soit plus court pour les ufs déposés par les individus de la saison humide serait dû à ce que, lorsque ces femelles auront atteint leur maturité, l'extrême humidité du sol ne permettra pas la ponte qui se trouvera ainsi retardée.Les tentatives faites en laboratoire, pour croiser entre eux des adultes génitalement mûrs provenant de chacune de ces 2 populations, ont échoué.La phénologie de la population de la saison sèche reste la même, que celle-ci soit élevée au laboratoire ou dans la nature.Les caractéristiques de la croissance de ces Orthoptères sont conformes à la règle de Dyar. Toutefois, tandis que cette croissance est linéaire quand on la mesure d'après la longueur du corps, on y relève deux phases si l'on se réfère au poids des individus, la divergence se manifestant à partir du 4 e stade larvaire.
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10.
Larvae of the caddisTrichostegia minor (Curtis) were collected from four woodland pools in The Netherlands, three of which are temporary, from August 1986 till June 1987. Eggs and larvae of this species proved to be very well adapted to drought, freezing, strongly fluctuating pH and alkalinity levels and prolonged oxygen deficit. The life cycle ofT.minor in a small woodland marsh overgrown byCalla palustris took one year. Adult flight period started at the end of May. Oviposition took place independent of water. Hatching of the eggs started in September and was probably induced by immersion. During the larval stage from September until May, 5 instars could be distinguished by the size of the head capsule. Growth of instars I, II and III during autumn was moderate. Most larvae overwintered as instar III or IV. Possibly there was a larval diapause during winter. In spring rapid growth to instar V took place prior to pupation. Growth rate, expressed as the increase of mean individual dry weight was highest from March to April (2.05±0.75% DW.m–2.d–1). In extremely shallow water growth in spring was initially more rapid compared to growth in deeper water. During winter the growth rate decreased to 0.038±0.071% DW.m–2.d–1. Net annual production based on the changes of momentary biomass was 183.2±31.7 mg DW.m–2.y–1 or 177.2±31.3 mg AFDW.m–2.y–1. Production loss during the winter season was 75.1±10.8 mg DW.m–2.y–1 or 72.3±10.6 mg AFDW.m–2.y–1.  相似文献   

11.
The essential oils obtained from fresh leaves, flowers, roots and stems of Unxia camphorata collected in the rainy and dry seasons in the state of Pará, were examined by GC and GC/MS. The highest oil yields were observed from the samples collected at the dry season (flowers: 0.6%, leaves: 0.6%, stems: 0.3%, roots: 0.4%). All parts of the plant were rich in α-phellandrene, with non-significant changes during the rainy and dry seasons (flowers: 61.9–53.7%, leaves: 18.3–17.4%, stems: 68.3–72.8%, roots: 51.9–48.3%). In the leaf oil, the monoterpenoid camphor was the largest component (rainy season: 28.5%, dry season: 28.8%). In the leaf oil, the high amount of α-phellandrene was followed by methylthymol (rainy season: 14.1%, dry season: 13.1%). Depending on the plant part studied, these oils can be characterized by α-phellandrene, camphor/α-phellandrene/camphene, or α-phellandrene/methylthymol type.  相似文献   

12.
We analyzed population dynamics and birth seasonality of wild bonobos at Wamba, Democratic Republic of the Congo, based on 20 years of observations (1976–1996). Wamba Bonobo infant mortality is much lower than that reported for chimpanzees. This seemes to be related to several socioecological characteristics of bonobos: the use of abundant fruit and herbaceous foods, larger food patch size, female feeding priority, and the absence of infanticide. The mean interval between live births of 4.8 years is shorter than those reported for chimpanzees, and some females simultaneously carried and nursed two successive offspring. Mother–offspring conflicts, such as refusal of suckling attempts and interference with mothers' copulation, which are common in chimpanzees, are rare in Wamba bonobos. A birth peak seems to occur during the light rainy season from March to May, just after the season with the least rainfall. This timing of births is similar to those reported for chimpanzee populations, and might benefit both mother and offspring by maximizing the amount of time before the next dry season.  相似文献   

13.
Ecological problems of Lake Ladoga: causes and solutions   总被引:3,自引:3,他引:0  
We studied the outcome of competition between a large (Brachionus calyciflorus) and a small (Anuraeopsis fissa) rotifer species at five algal (Scenedesmus acutus) concentrations (0.5 × 106 to 40.5 × 106 cells ml–1) and with varying initial densities in mixed populations (100 to 0% of B. calcyciflorus or A. fissa), the combined initial biomass being 0.2 µg ml–1 in all test jars. Experiments were conducted at 28 ± 1 °C.Regardless of food concentration, B. calcyciflorus showed a greater increase in biomass than A. fissa, peak densities (mean ± standard error) at the lowest food concentration in the controls being 1.34 ± 0.31 µg dry weight ml–1 and 0.82 ± 0.08 dry weight ml–1, respectively. At the lower food concentrations, A. fissa displaced B. calyciflorus and vice versa at the higher food concentrations. At the intermediate food concentrations of 4.5 × 106 cells ml–1, B. calyciflorus outcompeted A. fissa only if its initial population density was three times higher. The rates of population growth in controls varied from 0.792 ± 0.06 d–1 to 1.492 ± 0.13 d–1 for B. calyciflorus and 0.445 ± 0.04 to 0.885 ± 0.01 for A. fissa depending on food level. When both species were introduced together, low food levels favoured higher abundance of A. fissa than B. calyciflorus, suggesting, in nature, it is likely that small Anuraeopsis colonize oligotrophic water bodies more successfully than larger Brachionus. The results also suggest that the outcome of competition depends not only on the size of the competing species and food availability but also on their colonizing density.  相似文献   

14.
The present distribution of the invasive brown alga Sargassum muticum in the southwest Netherlands is updated. Populations of the alga were found to remain at their 1985 level in Lake Grevelingen, with a small eastward expansion into the Eastern Scheldt estuary. A new population for the brackish, non-tidal Lake Veere is reported. Within Lake Grevelingen S. muticum forms a persistent, extensive canopy of 100% cover (4,442.5 ± 525.6 g fresh wt m–2, 640.3 ± 75.8 g dry wt m–2) that has a marked effect upon the penetration of photosynthetically active radiation (PAR) (reduced by 97% at 0.1 m). Surface sea water temperatures can be elevated by 2.7 °C above water not associated with a Sargassum canopy; furthermore, the dense canopy shades and hence reduces water temperatures below 0.1 m depth. Productivity studies indicate that assimilation occurs in the upper levels of the canopy (57.09 µg C mg dry wt–1 m–2 at a mean PAR rate of 106.7 J cm–2 h–1). Self-shading and a resultant decrease in the rate of assimilation was evident below the canopy.  相似文献   

15.
The African wild ass (Equus africanus) is the most endangered wild equid in the world and is listed as a Critically Endangered (CR) on the IUCN Red list. Today, only relict populations remain in Ethiopia and Eritrea. The current Ethiopian population persists in the Danakil Desert at a very low density. Wildlife managers need to identify the extent of the remaining suitable habitat and understand human–wildlife interactions for appropriate conservation strategies. This study employed the maximum entropy model (Maxent) to determine suitable habitat and seasonal distribution of African wild ass in the Danakil Desert of Ethiopia. Field surveys were conducted four times annually, twice during the wet season and twice during the dry season, for 2 years. Field data and predictor variables were separated into the dry and wet seasons, and models were generated for each season independently. Distance from water, distance from settlements, herbaceous cover and slope were the best predictors of suitable habitat for both dry and wet seasons. Evaluations of model performances were high with area under the curve (AUC) values of 0.94 and 0.95 for the dry and wet seasons, respectively. Our results will be critical for identifying the available suitable habitat that should be conserved to safeguard this species from extinction.  相似文献   

16.
The response of rice toAzolla caroliniana, newly introduced in India, was compared with the reponse to the local isolate ofAzolla pinnata at varying rates of phosphate fertilizer (4.4–8.8 kg P ha–1) during a wet and a dry season.Fresh weight, dry weight and fixed N were more for both species 21 DAI (days after inoculation) than 14 DAI, but acetylene reduction activity (ARA) was higher 14 DAI than 21 DAI. Dry weight of Azolla and fixed N were less 14 DAI forA. caroliniana than forA. pinnata during the wet season. Twenty-one DAI, fresh weight ofA. caroliniana was 62.1 and 27.6% higher than that ofA. pinnata during the wet and dry season, respectively. However, dry weight and fixed N were more 21 DAI inA. caroliniana than inA. pinnata during only the wet season. The ARA was higher inA. caroliniana both 14 and 21 DAI, irrespective of season. The presence of either species in the rice field increased grain yield, straw yield, number of panicles m–2, number of grains per panicle and reduced percentage sterility during both the wet and the dry season. Phosphate application significantly increased fresh weight, dry weight, ARA and fixed N for both species as well as grain and straw yields of rice. The responses to phosphate fertilizer were similar for both Azolla species and for rice grown with either one of the Azolla species.  相似文献   

17.
Phenological shifts may play a role in the success of invasive species, especially in association with climatic variability. We studied the response of a North American population of the invasive plant, Lythrum salicaria L., to changes in local climate associated with the El Niño/Southern Oscillation Event (ENSO) of 1997–1998. For L. salicaria plants at two wetland sites near North Bay, Ontario, Canada, we made weekly observations of flowering phenology and monthly measurements of aboveground biomass during the 1997 and 1998 growing seasons (April–October). Reproductive output was measured as cumulative length and biomass of inflorescences at the end of the growing season. Temperature and precipitation during the 1997 growing season were typical for the region and provided good baseline data for comparison to the full effects of the ENSO event in 1998, which increased spring temperatures and reduced precipitation in the study area. In response to these conditions, populations of L. salicaria began to flower 14 days earlier (Julian day = 181 ± 10) in 1998 than in 1997 (Julian day = 195 ± 12), and accumulated more aboveground biomass early in the growing season (P < 0.05). However, by the end of the growing season, there were no significant differences between years in aboveground biomass or total inflorescence lengths, and senescence of plants occurred at similar times for both growing seasons. Advances in spring phenology during ENSO events offer several potential advantages to L. salicaria, and could have a significant impact on biological control programs initiated for this species in North America.  相似文献   

18.
Elephant populations are in decline across the African continent, but recent aerial surveys show that populations in Uganda are increasing. However, threats such as poaching and habitat disturbance remain. Having a comprehensive knowledge of the ranging behaviour of Ugandan elephants is crucial to understanding where critical habitat for the species occurs. We investigated various aspects of ranging behaviour of 45 radio-collared elephants (Loxodonta africana) in three areas—Queen Elizabeth Protected Area (QEPA), Murchison Falls (MFPA) Protected Area and Kidepo Valley (KVCA) Conservation Area. We also set Ugandan analyses in a continental context by comparison with home ranges reported in published literature. Elephants within KVCA had larger core ranges than elephants in QEPA or MFPA. Wet season ranges in KVCA were much larger than dry season ranges. The most important core areas in all three national parks were centred around water resources. Home range size was negatively correlated with net primary productivity (NPP) at Ugandan (N = 39 individuals) and continental (N = 17 sites) scales. This study indicates that, at a local scale, factors such as water source location are important in shaping elephant ranging behaviour. At larger scales, factors such as NPP are good predictors of elephant home range size.  相似文献   

19.
Understanding landscape-scale patterns of herding is critical in identifying and assessing the impacts of pastoral grazing. Here, a general model of herding is developed based on the Sukuma agropastoral system in the Rukwa Valley, Tanzania. Using this conceptual framework, the factors affecting the maximum distances herds travel from home and the distribution of grazing around pastoral settlements are examined. The distribution of dry season water structured the landscape-scale distribution of grazing throughout the year, not just during the dry season. Water availability strongly affected the distances herds ranged from home in the dry season and the distribution of grazing around pastoral settlements throughout the year. Associations between cattle productivity and herding practices were also examined. The effects of traveling further from home, keeping cattle in large herds, and using/living in areas of high settlement densities were examined on the following measures of productivity: intake rates, foraging behavior, milk yields, and body conditions. Cattle from larger herds were observed to walk more while actively foraging and engage in more walking bouts (taking ten steps without taking a bite). The increased walking of large herds may explain why they range farther from home and highlight the importance and ubiquity of herd splitting among pastoralists. However, herd size effects were not apparent in intake rates or milk yields. Milk yields were negatively affected by traveling farther from home. These data demonstrate substantial variability within herding populations and show interesting similarities with herding systems in substantially more arid areas.  相似文献   

20.
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