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211.
212.
Gregory J. Robertson 《Behavioral ecology and sociobiology》1998,43(4-5):289-296
Hypotheses regarding the evolution and maintenance of intraspecific nest parasitism were tested with data collected during
a 3-year study of common eiders (Somateria mollissima) breeding near Churchill, Manitoba. The nest parasitism rate was highest (42.4% of nests) during the year with the highest
nest density and the best environmental conditions, and lowest (20.2% of nests) in the year with the lowest nest density and
the poorest environmental conditions. Over the nesting season, parasitic eggs were laid at the same time as normally laid
eggs. Most parasitic eggs (>75%) were laid before the host female laid her third egg. The majority of the parasitic eggs were
the first or second egg produced by the parasitic female. When a parasitic egg was laid before or on the same day as the host
female initiated her clutch, the probability of her first egg being depredated before incubation was significantly lowered.
First- and second-laid eggs suffered a high rate of predation probably because nesting females do not attend their clutch
until their second or third egg is laid. Hypotheses that some females use intraspecific nest parasitism to parasitize the
parental care of other females were inconsistent with these data. Egg adoption is a likely explanation for the prevalence
of females incubating parasitic eggs in this population.
Received: 30 September 1997 / Accepted after revision: 6 May 1998 相似文献
213.
Numerical simulation of a fine-grained denitrification layer for removing septic system nitrate from shallow groundwater 总被引:1,自引:0,他引:1
Kerry T. B. MacQuarrie Edward A. Sudicky William D. Robertson 《Journal of contaminant hydrology》2001,52(1-4):29-55
One of the most common methods to dispose of domestic wastewater involves the release of septic effluent from drains located in the unsaturated zone. Nitrogen from such systems is currently of concern because of nitrate contamination of drinking water supplies and eutrophication of coastal waters. It has been proposed that adding labile carbon sources to septic distribution fields could enhance heterotrophic denitrification and thus reduce nitrate concentrations in shallow groundwater. In this study, a numerical model which solves for variably saturated flow and reactive transport of multiple species is employed to investigate the performance of a drain field design that incorporates a fine-grained denitrification layer. The hydrogeological scenario simulated is an unconfined sand aquifer. The model results suggest that the denitrification layer, supplemented with labile organic carbon, may be an effective means to eliminate nitrogen loading to shallow groundwater. It is also shown that in noncalcareous aquifers, the denitrification reaction may provide sufficient buffering capacity to maintain near neutral pH conditions beneath and down gradient of the drain field. Leaching of excess dissolved organic carbon (DOC) from the denitrification layer is problematic, and causes an anaerobic plume to develop in simulations where the water table is less than 5-6 m below ground surface; this anaerobic plume may lead to other down gradient changes in groundwater quality. A drain field and denitrification layer of smaller dimensions is shown to be just as effective for reducing nitrate, but has the benefit of reducing the excess DOC leached from the layer. This configuration will minimize the impact of wastewater disposal in areas where the water table is as shallow as 3.5 m. 相似文献
214.
Kathleen E. Reaugh-Flower George M. Branch Jean M. Harris Christopher D. McQuaid Bronwen Currie Arthur Dye Bruce Robertson 《Marine Biology》2010,157(10):2177-2185
Quantifying sessile marine invertebrate recruitment often requires destructive sampling or extrapolation from artificial substrata,
the latter introducing the danger of artifacts. We measured intertidal mussel recruitment into mussel beds and into brushes
at three-month intervals for five years across 3,200 km of southern Africa and determined substrata effects on recruitment
rate. Recruitment into mussel beds showed a strong, coast-wide gradient, with high recruitment on the West coast, diminishing
on the South coast, and increasing slightly on the East coast. At scales of 10 s of km, brushes reflected natural temporal
recruitment variability, with a strong significant linear correlation between recruitment into brushes and into mussel beds.
However, the relationship became semi-logarithmic when comparing among locations at a scale of 100 s of km. Artificial substrata
thus reflect local natural settlement well but may be a poor indicator of it when spatial scales are large, particularly when
mussel bed topography is complex, or localities have very different recruitment densities. 相似文献
215.
The Reproductive Health Response in Conflict (RHRC) Consortium designed a standardised questionnaire to measure gender-based violence (GBV) prevalence in conflict-affected settings. A preliminary field test was undertaken July-August 2002 in one urban and one rural district in East Timor to assess the prevalence of GBV among women 18-49 years of age during and after conflict. The field test used a cross-sectional survey design with a two-stage random selection process. During the year preceding East Timor's 1999 crisis, 23.8 per cent of respondents reported physical assault by an intimate partner; this rate was not significantly different in the year preceding the survey (24.8 per cent). Assault by perpetrators outside the family declined significantly from 24.2 per cent during the crisis to 5.8 per cent post-crisis for physical assault (p<.001) and 22.7 per cent during the crisis to 9.7 per cent post-crisis for sexual assault (p=0.046). The field test stimulated and informed additional research in East Timor, and the complementary findings of these research initiatives continue to be used to develop local policies and programming to prevent and address GBV. 相似文献
216.
The terms used to describe and negotiate environmental quality are both ambiguous and value-laden. Stakeholders intimately
and actively involved in the management of forested lands were interviewed and found to use ambiguous, tautological, and value-laden
definitions of terms such as health, biodiversity, sustainability, and naturalness. This confusing language hinders public
participation efforts and produces calls to regulate and remove discretion from environmental professionals. Our data come
from in-depth interviews with environmental management professionals and other stakeholders heavily vested in negotiating
the fate of forested lands. We contend that environmental science and management will be more effective if its practitioners
embrace and make explicit these ambiguous and evaluative qualities rather than ignore and disguise them. 相似文献
217.
Summary We monitored the time spent at the nest and following behavior of mated tree swallows to determine if males were guarding their mates. The proportion of time spent together at the nest did not decrease significantly between fertile and postfertile periods, and the tendency of males to follow females was not significantly different from that of females to follow males. Following by either sex was infrequent. We suggest that the lack of mate guarding in tree swallows is related to an apparently low probability of extra-pair copulations, which in turn is likely to be due to two factors. Nesting opportunities are limited, perhaps more so for females than males. If the operational sex ratio is skewed towards females, this would not only reduce the risk of extra-pair copulations, but would also select against promiscuous females which would risk being abandoned by their mates. Secondly, under natural conditions, the limited availability of nest sites has selected for territorial defense by both males and females, which may decrease the occurrence of extra-pair copulation. Both factors would lead to relaxed selection for mate guarding behavior. 相似文献
218.
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220.
Robertson Blair van Dam-Bates Paul Gansell Oliver 《Environmental and Ecological Statistics》2022,29(1):55-76
Environmental and Ecological Statistics - A spatial sampling design determines where sample locations are placed in a study area. To achieve reliable estimates of population characteristics, the... 相似文献