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81.
Jesús M. Avilés Juan J. Soler Nathan S. Hart 《Behavioral ecology and sociobiology》2011,65(9):1721-1730
It has been proposed that the blue-green bird egg colourations of many avian species may constitute a sexually selected female
signal that males can use to modulate their parental investment. A fundamental untested assumption for the validation of this
hypothesis is that males can accurately assess differences in the colour of eggs. A recent review suggests that this could
be particularly problematic when egg clutches were located within a dimly lit nest cavity, due to limitations of the visual
system in low light conditions. Here, we first used a photoreceptor noise-limited model of colour discrimination ability that
accounts for visual performance under low light conditions to study whether a typical cavity-nesting passerine, the spotless
starling Sturnus unicolor, can discriminate their eggs under the ambient illumination in their nest-holes. Secondly, we tested the validity of model
predictions with behavioural data collected in two egg discrimination experiments performed in this species. Estimated egg
detectability depended entirely on model assumptions about visual limitations linked to light intensity. Starlings would not
be able to discriminate egg differences in their nests if the model was based on the assumption that light intensity limited
detectability, whereas they could potentially perceive as different many possible pairwise clutch comparisons if the model
assumption was that light intensity did not limit detectability. Results of behavioural experiments fitted the prediction
of the visual model where light intensity did not limit detectability. Our results suggest that photoreceptor noise-limited
colour models based on stimulation of single photoreceptors cannot, at present, be used to predict egg discrimination ability
in spotless starlings under low light conditions. Future studies aiming to test egg discrimination constraints in the frame
of the sexual selection hypothesis should therefore combine both modelling and behavioural experiments to determine which
are the components of the models that produce the mismatch with the behavioural conditions. 相似文献
82.
83.
Relationships among Isolated Wetland Size, Hydroperiod, and Amphibian Species Richness: Implications for Wetland Regulations 总被引:6,自引:0,他引:6
Joel W. Snodgrass †‡ Mark J. Komoroski † A. Lawrence Bryan JR. † Joanna Burger 《Conservation biology》2000,14(2):414-419
Abstract: Wetland development within the United States is regulated primarily by size. Decisions concerning wetland destruction or conservation are therefore based in part on three inherent assumptions: (1) small wetlands contain water for short portions of the year; (2) small wetlands support few species; and (3) species found in small wetlands are also found in larger wetlands. We tested these assumptions using data on wetland size, relative hydroperiod (drying scores), and relative species richness of amphibians in depression wetlands of the southeastern United States. We found a significant (p = 0.03) but weak (r2 = 0.05) relationship between hydroperiod and wetland size and no relationship (p = 0.48) between amphibian species richness and wetland size. Furthermore, synthetic models of lentic communities predict that short-hydroperiod wetlands support a unique group of species. Empirical investigations support this prediction. Our results indicate that hydroperiod length should be included as a primary criterion in wetland regulations. We advocate a landscape approach to wetlands regulation, focused in part on conserving a diversity of wetlands that represent the entire hydroperiod gradient. 相似文献
84.
85.
M. S. Mooring A. A. McKenzie Benjamin L. Hart 《Behavioral ecology and sociobiology》1996,38(4):259-266
The lesser mouse lemur (Microcebus murinus) is a prosimian primate which presents evidence of sex ratio bias of offspring that agrees with the direction of bias predicted
by the local resource competition model for facultative sex ratio adjustment. That is, females overproduced sons when grouped
prior to mating, whereas isolated females exhibited the opposite tendency. In this solitary species, social communication
relies heavily on urinary chemical signals. To test the hypothesis that sex biases induced by social factors may be linked
to urinary cues, isolated females were exposed (n = 76) or not (control group, n = 16) to urinary cues from other reproductively active females from the beginning of the breeding season (induced by long
photoperiod) until oestrus. During that period, females were either continuously (n = 17) or partially (n = 59) exposed to chemosignal stimulation. Females in oestrus were placed in contact with a breeding male and subsequently
isolated until they gave birth. All females entered oestrus but the timing of oestrus was significantly delayed by 1 week
in urine-exposed females. A general depressive effect of long-term urine exposure on fecundity was demonstrated, involving
fewer impregnations, higher abortion frequency and smaller litter sizes. Among females giving birth (n = 55) to a total of 129 young, a significant positive correlation was found between sex ratio bias towards males and the
duration of urine exposure. However, the shift in sex ratio at birth depended on the duration of urine stimulation during
a sensitive period extending from the beginning of the long photoperiod until the beginning of the follicular phase. In the
absence of urinary cues during the sensitive period, females significantly overproduced daughters (32% males of 53 newborn).
As urine exposure increased during the sensitive phase, the proportion of males in litters increased from 54% males (n = 50) in partially urine-exposed females to a significant bias towards males (69.2% of 26 newborn) in totally exposed females.
The biased sex ratio in response to chemical cues did not show consistent relationships with maternal body weight, parity
or litter size. Although the intrinsic mechanisms involved in sex-biased conceptions are not known, chemical cues could interact
with the photoperiodic control of gonadotropin secretions.
Received: 14 January 1995/Accepted after revision: 26 November 1995 相似文献
86.
87.
TIMOTHY J. SMYSER SCOTT A. JOHNSON L. KRISTEN PAGE CASSIE M. HUDSON OLIN E. RHODES JR. 《Conservation biology》2013,27(4):752-762
Translocations are an important tool for wildlife conservation, although progress in the field of reintroduction biology has been hindered by the ad hoc and opportunistic nature of many translocations. We used an experimental translocation to elucidate the role of raccoon roundworm (Baylisascaris procyonis) and inbreeding depression in the decline of the Allegheny woodrat (Neotoma magister), an endangered species. We translocated woodrats from genetically diverse populations in the core of the species range to 4 previously occupied sites (reintroductions) and 2 sites supporting genetically depauperate populations (reinforcements) in Indiana (U.S.A.). In 2 reintroduction sites and 1 reinforcement site, we distributed anthelmintic baits to passively deworm raccoons and reduce the risk of woodrat exposure to roundworms. The remaining sites served as controls. We used raccoon latrine surveys and fecal flotation to monitor temporal variability in roundworm prevalence and effect of treatment. We used live trapping and microsatellite genotyping to monitor the demographic and genetic response of translocated populations over the following 54 months. At the conclusion of the study, 4 of 6 translocations were successfully maintaining abundance through local recruitment. The distribution of anthelmintic baits reduced levels of roundworm contamination, but levels of contamination were also low in 2 of 3 control sites. Reintroductions failed at control sites, one of which was due to high roundworm exposure. The other failed control reintroduction was likely attributable to demographic stochasticity and limited reproductive potential following initial mortality within the first 4 months. In both control and treatment reinforcements, increases in both allelic richness and heterozygosity were accompanied by increases in abundance, which is suggestive of genetic rescue. Our results demonstrate that mitigation of roundworm exposure through the distribution of anthelmintic baits can facilitate woodrat recovery and that diversity within genetically depauperate populations can be restored through the introduction of a limited number of individuals. El Uso de Reubicaciones Experimentales de Neotoma magister para Descifrar Agentes Causales de Disminución 相似文献
88.
Characterization of the syngas produced in the gasification process has been performed at commercial-scale Energy-from-Waste plants under various conditions of lambda value and syngas temperature. The lambda value from the gasification process is here defined as the ratio of the gasification air to the total stoichiometric air for complete combustion of the fuel input. Evaluation of the syngas calorific value has been performed by three different methods, i.e., estimation of the syngas calorific value from continuous in-line process measurements by mass and energy conservation equations, measurement of the syngas composition based on gas chromatography and calculation of the Gross Calorific Value from the measured composition, and direct continuous measurement of the calorific value using based on gas calorimeter. 相似文献
89.
Women and Wildlife in Southern Africa 总被引:4,自引:0,他引:4
MALCOLM L. HUNTER JR. ROBERT K. HITCHCOCK BARBARA WYCKOFF-BAIRD† 《Conservation biology》1990,4(4):448-451
90.
The study has investigated the levels of metal contamination in groundwater due to particulate matter fallout and leaching from ash pond and assigned contamination indices for the adjacent localities around an ash disposal site with application of geographic information systems (GIS). Fe, Ba, Cu, Mn, S, Pb, V, and Zn were found to be the major contaminants in groundwater. Enrichment factors (EF) of these elements with respect to the United States Environmental Protection Agency (USEPA) maximum contaminant levels show high values for Mn, Fe, and Pb in groundwater. The zone of attenuation for Ba, Fe, Cu, Mn, S, and Zn in groundwater is about 600-900 m from the ash pond, while Pb did not show any significant attenuation even at a distance of 1200 m. Tube wells around Rankasingha and Kukurhanga villages are most contaminated whereas open wells of Lachhmanpur, Kaniapada, and Kurudul villages showed higher degrees of contamination. 相似文献