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71.
We analyzed the relation of the amount and spatial pattern of land cover with stream fish communities, in-stream habitat,
and baseflow in 47 small southeastern Wisconsin, USA, watersheds encompassing a gradient of predominantly agricultural to
predominantly urban land uses. The amount of connected impervious surface in the watershed was the best measure of urbanization
for predicting fish density, species richness, diversity, and index of biotic integrity (IBI) score; bank erosion; and base
flow. However, connected imperviousness was not significantly correlated with overall habitat quality for fish. Nonlinear
models were developed using quantile regression to predict the maximum possible number of fish species, IBI score, and base
flow for a given level of imperviousness. At watershed connected imperviousness levels less than about 8%, all three variables
could have high values, whereas at connected imperviousness levels greater than 12% their values were inevitably low. Connected
imperviousness levels between 8 and 12% represented a threshold region where minor changes in urbanization could result in
major changes in stream condition. In a spatial analysis, connected imperviousness within a 50-m buffer along the stream or
within a 1.6-km radius upstream of the sampling site had more influence on stream fish and base flow than did comparable amounts
of imperviousness further away. Our results suggest that urban development that minimizes amount of connected impervious surface
and establishes undeveloped buffer areas along streams should have less impact than conventional types of development. 相似文献
72.
73.
Overview of case studies on recovery of aquatic systems from disturbance 总被引:13,自引:2,他引:13
Gerald J. Niemi Philip DeVore Naomi Detenbeck Debra Taylor Ann Lima John Pastor J. David Yount Robert J. Naiman 《Environmental management》1990,14(5):571-587
An extensive review of the published literature identified more than 150 case studies in which some aspect of resilience in
freshwater systems was reported. Approximately 79% of systems studied were lotic and the remainder lentic. Most of the stressor
types were chemical with DDT (N=29) and rotenone (N=15) the most common. The most common nonchemical stressors were logging
activity (N=16), flooding (N=8), dredging (N=3), and drought (N=7).
The variety of endpoints to which recovery could be measured ranged from sparse data for phytoplankton (N=13), periphyton
(N=6), and macrophytes (N=8) to relatively more data for fish (N=412) and macroinvertebrates (N=698). Unfortunately the same
characteristics were rarely measured consistently among sites. For example, with respect to fish, more than 30 different species
were studied and recovery was measured in many ways, most commonly on the basis of: (1) first reappearance of the species,
(2) return time of predisturbance densities, and (3) return time of predisturbance average individual size. Based on these
criteria, all systems in these studies seem to be resilient to most disturbances with most recovery times being less than
three years. Exceptions included when (1) the disturbance resulted in physical alteration of the existing habitat, (2) residual
pollutants remained in the system, or (3) the system was isolated and recolonization was suppressed. 相似文献
74.
M. Scheffer J. M. Baveco D. L. DeAngelis K. A. Rose E. H. van Nes 《Ecological modelling》1995,80(2-3)
Modelling populations on an individual-by-individual basis has proven to be a fruitful approach. Many complex patterns that are observed on the population level have been shown to arise from simple interactions between individuals. However, a major problem with these models is that the typically large number of individuals needed requires impractically large computation times. The common solution, reduction of the number of individuals in the model, can lead to loss of variation, irregular dynamics, and large sensitivity to the value of random generator seeds. As a solution to these problems, we propose to add an extra variable feature to each model individual, namely the number of real individuals it actually represents. This approach allows zooming from a real individual-by-individual model to a cohort representation or ultimately an all-animals-are-equal view without changing the model formulation. Therefore, the super-individual concept offers easy possibilities to check whether the observed behaviour is an artifact of following a limited number of individuals or of lumping individuals, and also to verify whether individual variability is indeed an essential ingredient for the observed behaviour. In addition the approach offers arbitrarily large computational advantages. As an example the super-individual approach is applied to a generic model of the dynamics of a size-distributed consumer cohort as well as to an elaborate applied simulation model of the recruitment of striped bass. 相似文献
75.
Within the rotational scheme developed by the Programme to fight the resistance of Simulium damnosum to chemical larvicides, there was an operational gap at discharges between 5 and 70 m3 s−1 for the treatment of rivers where resistance to organophosphates was present. The use of permethrin and carbosulfan was precluded because of risk of environmental impact and, Bacillus thuringiensis ser. H-14 treatments were not envisageable due to cost and logistics constraints. Among the possible complementary groups of larvicides tested, the pseudo-pyrethroids, held promise, because of a mode of action similar to that of pyrethroids, but along with a usually lower toxicity for fish. Etofenprox, one of the pseudo-pyrethroids tested, shows a global detachment of non-target insects in 24 h close to that of pyraclofos, an organo-phosphorus compound (27 against 23%). In laboratory conditions, six times the operational dose which is 0.03 mg l−1 10 min, is needed to cause 50% mortality of Caridina sp. (a small shrimps species) and 30 times this same dose for 95% mortality. For fish species, a safety margin of 400–800 times the operational dose is observed for Oreochromis niloticus and 200–400 times for Tilapia zillii. 相似文献
76.
Many fishes are characterized by intense sperm competition between males that use alternative mating tactics. In externally
fertilizing fishes, males’ proximity to females during spawning can be an important determinant of fertilization success.
Here, we assess how mating tactic, body length, speed during streak spawns, and periphery cover affect males’ proximity to
females during sperm competition in the externally fertilizing bluegill (Lepomis macrochirus). Bluegill are characterized by three mating tactics referred to as parental, sneaker, and satellite. Parentals are territorial
and construct nests, while sneakers use a streaking behavior, and satellites use female mimicry to steal fertilizations from
parentals. We show that a small body length is important for sneakers but not for satellites to obtain a close position to
the female during spawning. Specifically, smaller sneakers obtain a closer position to females than larger sneakers in part
by positioning themselves closer on the periphery of a parental’s nest before streaking but show no difference in the speed
at which they streak. The amount of peripheral vegetation around a parental’s nest did not appear to affect proximity of sneakers
to females, and there was no relationship between the amount of peripheral vegetation and the frequency of intrusions by either
sneakers or satellites. Finally, parentals were farther from the female when a sneaker or satellite intruded than when they
spawned alone with the female. 相似文献
77.
Alejandra Valero Robyn Hudson Edgar Ávila Luna Constantino Macías Garcia 《Behavioral ecology and sociobiology》2005,59(2):262-269
When approached by males, females of the Amarillo fish (Girardinichthys multiradiatus) perform a behaviour called vibration or they are aggressively challenged. We quantified vibration and assessed whether it compromises the rate of feeding attempts in dyads kept in outdoor enclosures. Male approaches resulted in female vibration and in a reduced feeding rate. Vibration was not evoked by female–female aggression, which was frequent and always ended in the subordinate fleeing from the dominant female. Using a closed respirometer we found that vibration is costly; oxygen consumption of females was greater in the presence of a male (which evoked vibration) than in the presence of a non-familiar female (when no vibration occurred). By recording interactions of females confined in aquaria in the presence and in the absence of males, we confirmed that escaping is the only available response to deal with female aggression. Females kept without males participated in frequent aggressive (even lethal) interactions that did not abate while the subordinate female was in sight of the dominant, and which caused premature births and injuries. Yet in the alternative treatment aggression ceased when a male approached, prompting vibration in both females. Thus, in the Amarillo, in as much as it evokes energetically costly female vibrations, male courtship is an expression of sexual conflict. However, in the absence of males, frequent female aggression potentially annuls the benefits of not vibrating. We propose that a complete appraisal of the consequences of sexual conflict must include an assessment of the costs imposed by intra-sexual interactions. 相似文献
78.
On thresholds and environmental curve tensiometers 总被引:1,自引:0,他引:1
This paper considers distinctions between lognormal and mixture models. Emphasis is placed on two component mixtures where the lower valued subpopulation has a large mixing parameter. The density of this sort of mixture can be easily mistaken for a lognormal density. In order to compare such a mixture to a lognormal it is demonstrated that Galton's two parameter logmodel and Pearson's five parameternormal mixture are special, or limiting, cases of the same general mixture model. Consideration is given to the lognormal threshold parameter in order to devise a tool that can help distinguish mixtures from lognormals. Based on the threshold parameter, piloted procedures can help measure whether or not a curve is friable, in the sense that a brittle curve is better represented as a mixture than as a skewed lognormal. It is also shown that generalizations of Galton's product risk model can be represented interms of the threshold parameter Based on a tool called a curve tensiometer was designed to be applied as a graphical friability check in the ecological context of Fisher's classic Iris data and in the environmental context of a Santa Monica Bay fish consumption study. 相似文献
79.
80.
Jennifer F. Lind‐Riehl Audrey L. Mayer Adam M. Wellstead Oliver Gailing 《Conservation biology》2016,30(6):1288-1296
The U.S. Endangered Species Act (ESA) requires that the “best available scientific and commercial data” be used to protect imperiled species from extinction and preserve biodiversity. However, it does not provide specific guidance on how to apply this mandate. Scientific data can be uncertain and controversial, particularly regarding species delineation and hybridization issues. The U.S. Fish and Wildlife Service (FWS) had an evolving hybrid policy to guide protection decisions for individuals of hybrid origin. Currently, this policy is in limbo because it resulted in several controversial conservation decisions in the past. Biologists from FWS must interpret and apply the best available science to their recommendations and likely use considerable discretion in making recommendations for what species to list, how to define those species, and how to recover them. We used semistructured interviews to collect data on FWS biologists’ use of discretion to make recommendations for listed species with hybridization issues. These biologists had a large amount of discretion to determine the best available science and how to interpret it but generally deferred to the scientific consensus on the taxonomic status of an organism. Respondents viewed hybridization primarily as a problem in the context of the ESA, although biologists who had experience with hybridization issues were more likely to describe it in more nuanced terms. Many interviewees expressed a desire to continue the current case‐by‐case approach for handling hybridization issues, but some wanted more guidance on procedures (i.e., a “flexible” hybrid policy). Field‐level information can provide critical insight into which policies are working (or not working) and why. The FWS biologists’ we interviewed had a high level of discretion, which greatly influenced ESA implementation, particularly in the context of hybridization. 相似文献