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661.
Slope,aspect and climate: Spatially explicit and implicit models of topographic microclimate in chalk grassland 总被引:2,自引:0,他引:2
Jonathan Bennie Brian Huntley Andrew Wiltshire Mark O. Hill Robert Baxter 《Ecological modelling》2008
The slope and aspect of a vegetated surface strongly affects the amount of solar radiation intercepted by that surface. Solar radiation is the dominant component of the surface energy balance and influences ecologically critical factors of microclimate, including near-surface temperatures, evaporative demand and soil moisture content. It also determines the exposure of vegetation to photosynthetically active and ultra-violet wavelengths. Spatial variation in slope and aspect is therefore a key determinant of vegetation pattern, species distribution and ecosystem processes in many environments. Slope and aspect angle may vary considerably over distances of a few metres, and fine-scale species’ distribution patterns frequently follow these topographic patterns. The availability of suitable microclimate at such scales may be critical for the response of species distributions to climatic change at much larger spatial scales. However, quantifying the relevant microclimatic gradients is not straightforward, as the potential variation in solar radiation flux under clear-sky conditions is modified by local and regional variations in cloud cover, and interacts with long-wave radiation exchange, local meteorology and surface characteristics. 相似文献
662.
Ecological network analysis (ENA) is a modeling approach increasingly being used to evaluate food webs and provide an ecosystem-based approach to resource management. Unfortunately, validation of ENA output is rarely performed. This study represents part of a larger effort to critically evaluate ENA. Here we validate ENA output using stable isotope analysis (SIA), and where validation is not met, determine the effects of modifying trophic networks to reflect validation. 相似文献
663.
Summary. Although terrestrial turtles have served as a model for studies of olfactory neurophysiology, little is known about how they
use chemical information in an ecological sense. We tested whether box turtles (Terrapene carolina) use chemical information to distinguish between predatory and nonpredatory mammals. Box turtles in our study exhibited more
escape behavior when exposed to urine from a predator (coyote, Canis latrans) than when exposed to urine from a nonpredator (white-tailed deer, Odocoileus virginianus) or a blank control. Escape behavior is consistent with an antipredator response. In addition, the turtles decreased their
handling time for food when in the presence of urine from either species of mammal in comparison to the blank, indicating
that chemical cues from mammals in general may result in increased vigilance by terrestrial turtles. Examination of a variety
of response variables may be important for adequate assessment of the ecological role of chemosensory behavior. 相似文献
664.
We estimated the annual adult survival (S) of several species of temperate and tropical sexually dimorphic tanagers and manakins from the proportions of first-year and older individuals in museum collections. In the case of the sexually dimorphic species included here, young males through their first year resemble females and can be distinguished from older males. We assumed that the sex ratio among first-year birds is even and estimated the number of immature females (IF) in a sample as equal to the number of immature males (IM), using sex information on museum labels. The number of adult females (AF) is the total number of females (F) minus IF, and survival can be estimated by S = AF/F. We used a Monte Carlo resampling approach to estimate standard errors and 1% and 99% confidence limits on S for samples of size N, based on 1000 sets of N randomly drawn individuals and observed proportions of the F, IM, and AM classes. Estimates of annual survival (S) were 0.60-0.73 in four North American species of Piranga tanagers and 0.50 and 0.62 in two montane Central American species. Values of S in lowland species of Habia and Ramphocelus tanagers ranged between 0.68 and 0.82. Annual survival in Pipra manakins was 0.53-0.68, and values for two Manacus species were 0.69 and 0.70. Where estimates of apparent survival (phi) from capture-recapture studies were available, the two methods produced correlated results with a tendency for phi < S. Among tanagers, only Ramphocelus dimidiatus (0.82) and Piranga bidentata (0.50) stood out from the other species, for which S averaged 0.66 +/- 0.05 (SD). Annual survival rates of temperate and tropical species overlapped broadly in this analysis, reinforcing the conclusion that distinctive life-history traits of temperate vs. tropical species cannot be explained completely by the adjustment of reproductive investment in relation to adult survival and the expectation of future life. 相似文献
665.
Social information use is a process across time, space, and ecology, reaching heterospecifics 总被引:2,自引:0,他引:2
Decision making can be facilitated by observing other individuals faced with the same or similar problem, and recent research suggests that this social information use is a widespread phenomenon. Implications of this are diverse and profound: for example, social information use may trigger cultural evolution, affect distribution and dispersal of populations, and involve intriguing cognitive traits. We emphasize here that social information use is a process consisting of the scenes of (1) event, (2) observation, (3) decision, and (4) consequence, where the initial event is a scene in such a process of another individual. This helps to construct a sound conceptual framework for measuring and studying social information use. Importantly, the potential value of social information is affected by the distance in time, space, and ecology between the initial observation and eventual consequence of a decision. Because negative interactions between individuals (such as direct and apparent competition) also depend on the distance between individuals along these dimensions, the potential value of information and the negative interactions may form a trade-off situation. Optimal solutions to this trade-off can result in adaptively extended social information use, where using information gathered some time ago, some distance away, and from ecologically different individuals is preferred. Conceivably, using information gathered from a heterospecific individual might often be optimal. Many recent studies demonstrate that social information use does occur between species, and the first review of published cases is provided here. Such interaction between species, especially in habitat selection, has important consequences for community ecology and conservation. Adaptively extended social information use may also be an important evolutionary force in guild formation. Complex coevolutionary patterns may result depending on the effect of information use on the provider of information. 相似文献
666.
Postfire response of flood-regenerating riparian vegetation in a semi-arid landscape 总被引:2,自引:0,他引:2
Piles of large wood (LW) deposited by major floods in river corridors can interact with naturally occurring wildfires from uplands to impact the regeneration of riparian vegetation. This study examines the spatial and short-term temporal response of riparian vegetation and soil nutrients to fire along the Sabie River, South Africa, with special emphasis on the effects of burned LW piles. At the study site there were 112 species of plants recorded with 28% of species restricted to the burned plots. As expected, vegetation cover was significantly lower in burned plots as compared with the unburned plots 12 months postfire. There was a significant influence of LW on species richness with fewer species recorded in the LW plots. For both fire and LW treatments, plant cover showed a significant change over three years. After an initial increase from 12 to 24 months (postfire) there was a decline in plant cover after 36 months. Species community composition was distinctly different between burned and unburned plots 12 months postfire, and the presence of LW affected species composition for burned plots but not for unburned ones. Time series ordination of LW plots highlighted the changes in species composition over the three years of sampling. Of trees with accumulations of LW within 5 m of their base, 48% had been killed by fire as compared to only 4% with no LW accumulations in close proximity. Soil-available P was significantly higher in the burned plots and even higher with burned LW while there were no effects on soil total N. There was also a significant positive trend between available P in soils and plant vegetation cover. Soil-exchangeable K was also significantly higher and total C significantly lower in the burned and LW plots. Burned plots also had significantly higher soil electrical conductivity (EC) and soil pH. The patchy nature of the studied fire, whose complexity is exacerbated by the distribution of flood deposited LW, acted to create a mosaic of alternate successional states as the riparian community recovers from flooding and the subsequent fire. We suspect that the resultant heterogeneity will increase ecosystem resilience by providing flexibility in the form of more options for a system response to subsequent disturbances. 相似文献
667.
On the choice of statistical models for estimating occurrence and extinction from animal surveys 总被引:1,自引:0,他引:1
Dorazio RM 《Ecology》2007,88(11):2773-2782
In surveys of natural animal populations the number of animals that are present and available to be detected at a sample location is often low, resulting in few or no detections. Low detection frequencies are especially common in surveys of imperiled species; however, the choice of sampling method and protocol also may influence the size of the population that is vulnerable to detection. In these circumstances, probabilities of animal occurrence and extinction will generally be estimated more accurately if the models used in data analysis account for differences in abundance among sample locations and for the dependence between site-specific abundance and detection. Simulation experiments are used to illustrate conditions wherein these types of models can be expected to outperform alternative estimators of population site occupancy and extinction. 相似文献
668.
Zheng B Wu D Wang B Liu X Wang M Wang A Xiao G Liu P Finkelman RB 《Environmental geochemistry and health》2007,29(2):103-108
In this study, investigations into endemic fluorosis were conducted and fluorine concentration in environmental samples determined.
In an indoor coal-combustion-type fluorosis area, local clay was used to mix with coal for indoor combustion. There are two
key steps in the procedure of the indoor transition of fluorine: indoor wet corns and vegetables strongly absorbed fluorine
from indoor air; and fluorine strongly accumulated in clay, which was mixed with coal for combustion. Therefore, with the
increasing of the percentage of clay in the clay-mixed coal as well as corn in foodstuff, the ratio of fluorosis will be increased. 相似文献
669.
Susan Kaaria Jemimah Njuki Annet Abenakyo Robert Delve Pascal Sanginga 《Natural resources forum》2008,32(1):53-63
This paper presents lessons from applying an innovative action research approach for linking smallholder farmers to markets, in eastern and southern Africa. The Enabling Rural Innovation (ERI) approach aims to strengthen social organization and entrepreneurial capacity in rural communities. It focuses on fostering community‐based capacity for the inclusion of rural women and the poor in analyzing and accessing market opportunities. Using case studies from Malawi and Uganda the paper assesses the outcomes of ERI on rural communities with a focus on human capital, gender issues and investment in natural resource management. Results show that households are benefiting significantly from linkages to markets in terms of increasing household incomes, and accumulating assets. Skills in analyzing markets and in negotiating with traders have increased among smallholder farmers. The integration of gender in the approach has led to changes in gender decision making patterns at household and community level towards a more shared decision‐making process. The results however show a difference in skills between men and women, with women showing lower levels of skills acquisition. Farmer participatory research has increased investments in improved technologies such as fertilizer applications for soil fertility management. 相似文献
670.