Determining the reproductive processes of benthic invertebrates is central to our understanding of their recruitment and population
dynamics. Sexual reproduction of the gonochoric and viviparous Great Barrier Reef sponge, Luffariella variabilis (Poléjaeff 1884) was quantified from histological samples collected over two reproductive seasons (2004 and 2005). Gametogenesis
commenced for females at a water temperature of 21°C, the lowest water temperature of the year. Spermatogenesis occurred above
22.5°C with sperm asynchronously developed and released from August or September to October. Oocytes developed asynchronously
from July to September, embryos from September to December, and larvae from November to December. Female reproduction terminated
in December (after larval release) prior to the highest mean annual water temperature of 30°C in January. There was a significant
(35%) decrease in female reproductive output in 2005 compared to 2004, as measured by the reproductive index (0.68 ± 0.12
female reproductive propagules mm−2 of mesohyl in 2005 compared with 1.05 ± 0.10 mm−2 in 2004). This corresponded with delayed oogenesis and spermatogenesis, and a shortened larval development cycle corresponding
with a delayed minimum temperature (21°C) in August of 2005 compared with July 2004. Accordingly, the maximum percentage of
the mesohyl occupied by female reproductive propagules (eggs, embryos and larvae) was also reduced by 60% in 2005 (overall
mean of 13.04% in October 2004 compared with 5.35% in October 2005). However, the mean sizes of individual female propagules
remained the same from year to year. Males in contrast, showed no overall difference in either reproductive index or percentage
occupation of the mesohyl between 2004 and 2005. The lowered reproductive output (∼35%) of females of L. variabilis associated with delayed minimum water temperatures may have important implications for population reproductive success where
oogenesis and spermatogenesis and larval release are cued by minimum and maximum water temperatures, respectively. 相似文献
Previous studies of relationships among the subspecies of snapping turtles ( Chelydra serpentina } based on morphological and osteological characters have been inconclusive. We investigated relationships among the four currently recognized subspecies using restriction endonuclease fragment patterns of mtDNA and protein electrophoresis. Sixteen six-based recognizing restriction endonucleases yielded 90 variable fragments that define 11 different haplotypes. Individuals of the two North American subspecies, C. s. osceola and C. s. serpentina , are closely related, differing by a maximum of 0.5% sequence divergence. The Central American subspecies, C. s. rossignonii and C. s. acutirostris , are more distinct, both from each other (a minimum of 1.7% sequence divergence) and from the North American samples (an average of 4.45% sequence divergence). The degree of allozymic variation among the four subspecies was found to be limited and could not be used to diagnose the four recognized subspecies. The mtDNA data presented here support the species-level distinctness of C. s. rossignonii and C. s. acutirostris from each other and from a C. s serpentina-C. s. osceola complex. The recognition of three distinctive groups of Chelydra rather than one widespread polytypic species has important conservation implications because it focuses attention on the poorly known middle and South American species. 相似文献
White-winged choughs (Corcorax melanorhamphos) are obligate cooperative breeders, living in groups which may contain up to 20 birds. Although breeding is dominated by
a single pair, all birds contribute to rearing young, including the provisioning of nestlings. However, some birds which have
carried food to the nest, even to the point of placing the food in the gaping mouth of a nestling, consume the food themselves
rather than provision the nestlings. Birds which fail to feed nestlings are typically young, and are only likely to fail to
deliver food when they cannot be observed by other group members. Birds which have just failed to deliver food are more likely
to engage in alternative helping behaviours such as allopreening the nestlings than are helpers which have just delivered
food in the conventional manner. Failure to deliver food is almost eliminated when foraging constraints are experimentally
reduced by supplemental feeding of the group. Collectively these observations suggest that young white-winged choughs act
deceptively by simulating helping behaviours without sacrificing food supplies.
Received: 24 January 1997 / Accepted after revision: 6 June 1997 相似文献
Summary. Stem volatile extracts from ten trees that are sympatric with the western pine beetle, Dendroctonus brevicomis LeConte (Coleoptera: Curculionidae) were assayed by gas chromatographic-electroantennographic detection analysis (GC-EAD).
The extracts were from the primary host, ponderosa pine, Pinus ponderosa Dougl. ex Laws. (Pinaceae); two nonhost angiosperms, California black oak, Quercus kelloggii Newb. (Fagaceae), and quaking aspen, Populus tremuloides Michx. (Salicaceae); and seven nonhost conifers, white fir, Abies concolor (Gord. & Glend.) Lindl. ex Hildebr. (Pinaceae), incense cedar, Calocedrus decurrens (Torr.) Florin (Cupressaceae), Sierra lodgepole pine, P. contorta murrayana Grev. & Balf. (Pinaceae), Jeffrey pine, P. jeffreyi Grev. & Balf. (Pinaceae), sugar pine, P. lambertiana Dougl. (Pinaceae), Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco (Pinaceae), and mountain hemlock, Tsuga mertensiana (Bong.) Carr. (Pinaceae). Sixty-four compounds were identified from the ten trees, 42 of which elicited antennal responses
in D. brevicomis, usually in both sexes. In addition, several synthetic compounds, including a number of the antennally-active compounds from
the extracted trees and some bark beetle pheromone components, elicited antennal responses in a manner similar to that observed
with the extracts. Of the antennally-active compounds known to be present in trees sympatric with D. brevicomis, only geraniol was unique to its host. Four antennally-active compounds were found in the host and in other conifers; five
compounds were found only in nonhost conifers; eight compounds were found in either or both of the nonhost angiosperms; eight
compounds were found in either or both of the angiosperms and in nonhost conifers, but not in the host; and 19 were found
in both the host and in angiosperms and/or nonhost conifers. Several bark beetle pheromone components were found in the stem
volatile extracts. Conophthorin was identified from both nonhost angiosperms; exo-brevicomin was identified in A. concolor; verbenone was identified from a number of nonhost conifers; and chalcogran was identified from P. tremuloides. The number of nonhost volatile chemicals that D. brevicomis encounters and is capable of detecting, and the diversity of sources from which they emanate, highlight the complexity of
the olfactory environment in which D. brevicomis forages. This provides a basis for further work related to chemically-mediated aspects of foraging in this insect and perhaps
other coniferophagous bark beetles, and highlights the need to consider foraging context in the design and implementation
of semiochemical-based management tactics for tree protection. 相似文献
The National Contaminant Biomonitoring Program (NCBP) was initiated in 1967 as a component of the National Pesticide Monitoring program. It consists of periodic collection of freshwater fish and other samples and the analysis of the concentrations of persistent environmental contaminants in these samples. For the analysis, the common approach has been to apply the mixed two-way ANOVA model to combined data. A main disadvantage of this method is that it cannot give a detailed temporal trend of the concentrations since the data are grouped. In this paper, we present an alternative approach that performs a longitudinal analysis of the information using random effects models. In the new approach, no grouping is needed and the data are treated as samples from continuous stochastic processes, which seems more appropriate than ANOVA for the problem. 相似文献
From towers constructed at the interface between second-growth forest and an active and an abandoned pasture, we observed inter-habitat movements of fruit-eating birds in eastern Amazônia. The abandoned pasture was composed of grasses and forbs with a scattering of shrubs and small trees. The active pasture contained a low, uniform bed of grass. A total of 47 frugivorous bird species was recorded in the second-growth forest. We observed that 18 of these species frequented the adjacent abandoned pasture but only 3 were found in the adjacent active pasture. Fruit-eating birds flying from second-growth forest typically spent only a few minutes in the abandoned pasture, and their movements were generally restricted to a pasture belt of 1–80 m along the border with the second-growth forest. Most inter-habitat movement occurred during the rainy season, which coincided with a peak in fruit availability in the abandoned pasture. Just three bird species, Ramphocelus carbo, Tachyphonus rufus , and Thraupis episcopus , accounted for an estimated 70% of the total movement of frugivores between the second-growth forest and the abandoned pasture. All three species spent most of their time in the abandoned pasture foraging on shrubs and trees but exhibited differences in their preference for specific habitat elements and in their seed-defecation habits. An understanding of bird behaviors in altered landscapes provides important information to planners and policy makers concerned with protecting regional biodiversity and maintaining landscape integrity. This research provides a rationale for placing limits on the size of clearings in the Brazilian Amazon. 相似文献
The Denver Basin Aquifer System (DBAS) is a critical groundwater resource along the Colorado Front Range. Groundwater depletion has been documented over the past few decades due to the increased water use among users, presenting long‐term sustainability challenges. A spatiotemporal geostatistical analysis is used to estimate potentiometric surfaces and evaluate groundwater storage changes between 1990 and 2016 in each of the four DBAS aquifers. Several key depletion patterns and spatial water‐level changes emerge in this work. Hydraulic head changes are the largest in the west‐central side of the DBAS and have decreased in some areas by up to 180 m since 1990, while areas to the northwest show increases in hydraulic head by over 30.5 m. The Denver and Arapahoe aquifers show the largest groundwater storage losses, with the highest rates occurring in the 2000s. The results highlight uncertainty in the volumetric predictions under various storage coefficient calculations and emphasize the importance of representative aquifer characterization. The observed groundwater storage depletions are due to a combination of factors, which include population growth increasing the demand for water, variable precipitation, and drought influencing recharge, and increased groundwater pumping. The methods applied in this study are transferable to other groundwater systems and provide a framework that can help assess groundwater depletion and inform management decisions at other locations. 相似文献
In this paper, we present an estimate of the predation impact of the global population of insectivorous birds based on 103 (for the most part) published studies of prey consumption (kg ha?1 season?1) of insectivorous birds in seven biome types. By extrapolation—taking into account the global land cover of the various biomes—an estimate of the annual prey consumption of the world’s insectivorous birds was obtained. We estimate the prey biomass consumed by the world’s insectivorous birds to be somewhere between 400 and 500 million metric tons year?1, but most likely at the lower end of this range (corresponding to an energy consumption of ≈?2.7?×?1018 J year?1 or ≈?0.15% of the global terrestrial net primary production). Birds in forests account for >?70% of the global annual prey consumption of insectivorous birds (≥?300 million tons year?1), whereas birds in other biomes (savannas and grasslands, croplands, deserts, and Arctic tundra) are less significant contributors (≥?100 million tons year?1). Especially during the breeding season, when adult birds feed their nestlings protein-rich prey, large numbers of herbivorous insects (i.e., primarily in the orders Coleoptera, Diptera, Hemiptera, Hymenoptera, Lepidoptera, and Orthoptera) supplemented by spiders are captured. The estimates presented in this paper emphasize the ecological and economic importance of insectivorous birds in suppressing potentially harmful insect pests on a global scale—especially in forested areas. 相似文献
Objective: Driver sleepiness is a major crash risk factor but may be underrecognized as a risky driving behavior. Sleepy driving is usually rated as less of a road safety issue than more well-known risky driving behaviors, such as drink driving and speeding. The objective of this study was to compare perception of crash risk of sleepy driving, drink driving, and speeding.
Methods: Three hundred Australian drivers completed a questionnaire that assessed crash risk perceptions for sleepy driving, drink driving, and speeding. Additionally, the participants' perceptions of crash risk were assessed for 5 different contextual scenarios that included different levels of sleepiness (low, high), driving duration (short, long), and time of day/circadian influences (afternoon, nighttime) of driving.
Results: The analysis confirmed that sleepy driving was considered a risky driving behavior but not as risky as high levels of speeding (P < .05). Yet, the risk of crashing at 4 a.m. was considered as equally risky as low levels of speeding (10 km over the limit). The comparisons of the contextual scenarios revealed driving scenarios that would arguably be perceived as quite risky because time of day/circadian influences were not reported as high risk.
Conclusions: The results suggest a lack of awareness or appreciation of circadian rhythm functioning, particularly the descending phase of circadian rhythm that promotes increased sleepiness in the afternoon and during the early hours of the morning. Yet, the results suggested an appreciation of the danger associated with long-distance driving and driver sleepiness. Further efforts are required to improve the community's awareness of the impairing effects from sleepiness and, in particular, knowledge regarding the human circadian rhythm and the increased sleep propensity during the circadian nadir. 相似文献