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21.
We investigated the type and extent of degradation at three sites on the Agulhas Plain, South Africa: an old field dominated
by the alien grass Pennisetum clandestinum Pers. (kikuyu), an abandoned Eucalyptus plantation, and a natural fynbos community invaded by nitrogen fixing—Australian Acacia species. These forms of degradation are representative of many areas in the region. By identifying the nature and degree
of ecosystem degradation we aimed to determine appropriate strategies for restoration in this biodiversity hotspot. Vegetation
surveys were conducted at degraded sites and carefully selected reference sites. Soil-stored propagule seed banks and macro-
and micro-soil nutrients were determined. Species richness, diversity and native cover under Eucalyptus were extremely low compared to the reference site and alterations of the soil nutrients were the most severe. The cover of
indigenous species under Acacia did not differ significantly from that in reference sites, but species richness was lower under Acacia and soils were considerably enriched. Native species richness was much lower in the kikuyu site, but soil nutrient status
was similar to the reference site. Removal of the alien species alone may be sufficient to re-initiate ecosystem recovery
at the kikuyu site, whereas active restoration is required to restore functioning ecosystems dominated by native species in
the Acacia thicket and the Eucalyptus plantation. To restore native plant communities we suggest burning, mulching with sawdust and sowing of native species. 相似文献
22.
Huei-Jen Tseng Ren-Chung Cheng Sheng-Hai Wu Sean J. Blamires I-Min Tso 《Behavioral ecology and sociobiology》2011,65(12):2351-2359
Animals may build multiple structures to provide benefits to counter the costs of building. Many orb web spiders add multiple
structures, e.g., barricading barrier webs and silk decorations, to their webs and these structures have been hypothesized
to function to deter predators or attract prey. The heavily armored spiny spiders construct barrier webs around their orb
webs and decorate them with conspicuous silk tufts. Why these organisms, already well protected by a thick cuticle and spines,
make the extra investment of building barrier webs and adding conspicuous silk decorations is not known. We predicted that
these structures function to both attract prey and deter predators. Field experiments were conducted in two consecutive years
using orb webs built by the East Asian spiny spider Thelacantha brevispina. We either (1) concealed the decoration, (2) removed the barrier webs, or (3) left the decorations and barrier webs intact.
We found year and treatment to interactively influence prey interception rates. In 2010, but not in 2009, we found prey interception
with T. brevispina webs to be greater when the decorations were conspicuous than when they were concealed suggesting that the decorations may
lure prey. Prey interception was lower when the barrier webs were present without decorations compared to when they were absent
without decorations. The prey-attracting function of the decorations thus may counter the reduction in prey interception incurred
by adding a barrier web. Predatory wasp interactions were not influenced by any of our treatments, probably because the spiders’
thick cuticle is the primary means of protection from wasps. Bird predation events, while rare, occurred only when decorations
were concealed or the barrier webs were removed. It is therefore plausible that the tuft decorations both lure prey and deter
birds. 相似文献
23.
Assessments of watershed condition for aquatic and riparian species often have to rely on expert opinion because of the complexity of establishing statistical relationships among the many factors involved. Such expert-based assessments can be difficult to document and apply consistently over time and space. We describe and reflect on the process of developing a computer-based decision support application from expert judgments for assessing aquatic and riparian conditions over the 100,000?km2 managed by the US federal government under the Northwest Forest Plan. The decision support system helped structure and document the assessment process and provided consistency and transparency to the evaluation methodology. However, many decisions and trade-offs were required in the expert engagement and model-building processes. Knowledge elicitation in an interactive group had a number of benefits over nominal group or Delphi processes, but efficient knowledge capture required considerable planning and expertise in the subject matter and modeling process. Communicating model results for validation was problematic and only effectively accomplished via in-person workshops. The choice to use different expert groups for each biophysical province provided more opportunities for participation and promoted greater ownership in the assessment, but it also led to increased variation among the resulting model structures. We propose three possible approaches for better managing the consistency of assessment models when multiple expert groups are involved. 相似文献
24.
In this paper we present a new approach describing population dynamics based on the view of a population as an oscillating system. To develop a mathematical model of an oscillating population, we applied a third-order differential equation. Our model describes population dynamics within a parametric-temporal continuum, formed by the relative values of population growth and decrease over time. In this paper we also illustrate how our oscillative model effectively compliments the existing suite of models in population dynamics. 相似文献
25.
Juliana Rangel Sean R. Griffin Thomas D. Seeley 《Behavioral ecology and sociobiology》2010,64(6):979-987
Animals that travel in groups must synchronize the timing of their departures to assure cohesion of the group. While most
activities in large colonies of social insects have decentralized control, certain activities (e.g., colony migration) can
have centralized control, with only a special subset of well-informed individuals making a decision that affects the entire
colony. We recently discovered that a small minority of individuals in a honeybee colony—an oligarchy—decides when to trigger
the departure of a swarm from its hive. The departure process begins with some bees producing the worker-piping signal (the
primer for departure) and is followed by these bees producing the buzz-run signal (the releaser for departure). In this study,
we determined the identity of these signalers. We found that a swarm’s nest-site scouts search for potential nest cavities
prior to the departure of the swarm from its hive. Furthermore, we found that the predeparture nest-site scouts are the sole
producers of the worker-piping signal and that they are the first producers of the buzz-run signal. The control of the departure
of a honeybee swarm from its hive shows how a small minority of well-informed individuals in a large social insect colony
can make important decisions about when a colony should take action. 相似文献
26.
Managing Baltic Sea fisheries under contrasting production and predation regimes: ecosystem model analyses 总被引:1,自引:0,他引:1
Based on an earlier published ecosystem model, we have explored possible effects of different management scenarios for the Baltic Sea. The scenarios include an oligotrophication of the system, a drastic increase in the number of seals, and changes in the fishery management. From these simulations we conclude that fisheries, seals, and eutrophication all have strong and interacting impacts on the ecosystem. These interactions call for integrated management. The modeling highlights the potential for conflicts among management mandates such as flourishing fisheries, rebuilt seal populations, and substantially reduced eutrophication. The results also suggest that fisheries management reference points have to be adjusted in response to changes in the presence of natural predators or ecosystem productivity. 相似文献
27.
Sean D Raj 《Water environment research》2005,77(7):3013-3018
Sales of bottled water have increased dramatically in recent years, with worldwide sales of more than dollars 35 billion, largely because of the public perception of purity and safety and public concern about the quality of tap water. Presently, there are no Food and Drug Administration (Washington, D.C.) recommendations regarding temperature and duration of storage for bottled water once it is opened and used. The objectives of this study were to examine the effects of time and storage temperature on bacterial growth and characterize the types of microorganisms contaminating bottled water after drinking once from the bottle. Bottled and tap water were tested using standard microbiology culture techniques. The bacterial count in bottled water increased dramatically, from less than 1 colony per milliliter (col/mL) to 38,000 col/mL over 48 hours of storage at 37 degrees C. Bacterial growth was markedly reduced at cold temperatures (refrigeration) compared with room temperature, with 50% fewer bacterial colonies in 24 hours and 84% fewer colonies in 48 hours. Interestingly, tap water resulted in only minimal growth, especially at cold temperatures (< 100 col/mL at 48 hours). These findings may be useful to increase public awareness and development of guidelines on storage temperature and expiration time for bottled water once it is opened and used. 相似文献
28.
29.
Sean A. Rands Richard A. Pettifor J. Marcus Rowcliffe Guy Cowlishaw 《Behavioral ecology and sociobiology》2006,60(4):572-581
In socially foraging animals, it is widely acknowledged that the position of an individual within the dominance hierarchy of the group has a large effect upon its foraging behaviour and energetic intake, where the intake of subordinates can be reduced through socially mediated interference. In this paper, we explore the effects of interference upon group dynamics and individual behaviour, using a spatially explicit individual-based model. Each individual follows a simple behavioural rule based upon its energetic reserves and the actions of its neighbours (where the rule is derived from game theory models). We show that dominant individuals should have larger energetic reserves than their subordinates, and the size of this difference increases when either food is scarce, the intensity of interference suffered by the subordinates increases, or the distance over which dominant individuals affect subordinates increases. Unlike previous models, the results presented in this paper about differences in reserves are not based upon prior assumptions of the effects of social hierarchy and energetic reserves upon predation risk, and emerge through nothing more than a reduction in energetic intake by the subordinates when dominants are present. Furthermore, we show that increasing interference intensity, food availability or the distance over which dominants have an effect also causes the difference in movement between ranks to increase (where subordinates move more than dominants), and the distance over which dominants have an effect changes the size of the groups that the different ranks are found in. These results are discussed in relation to previous studies of intra- and interspecific dominance hierarchies. 相似文献
30.
Sean O’Donnell 《Behavioral ecology and sociobiology》1996,38(2):83-88
Genetic variability within insect societies may provide a mechanism for increasing behavioral diversity among workers, thereby
augmenting colony efficiency or flexibility. In order to assess the possibility that division of labor has a genetic component
in the eusocial wasp Polybia aequatorialis, I asked whether the genotypes of workers within colonies correlated with behavioral specialization. Workers specialized
by foraging for one of the four materials (wood pulp, insect prey, nectar, or water) gathered by their colonies. I collected
foragers on 2 days from each of three colonies and identified the material the foragers were carrying when collected. I produced
random amplified polymorphic DNA (RAPD) markers from the genomic DNA of these foragers and estimated genotypic similarity
of foragers based on sharing of variable RAPD marker bands. Contingency tests on 20 variable loci per colony showed statistically
significant (P <0.05) biases in RAPD marker frequencies among forager types in the three colonies. Patterns of association of RAPD marker
bands with specializations were constant in two colonies, but changed between collection days in one colony. RAPD marker biases
suggest that division of labor among workers includes a genetic component in P. aequatorialis. Colony-level selection on variation in division of labor is a possible factor favoring the evolutionary maintenance of high
genotypic variability (low relatedness) in epiponine wasp colonies and in other eusocial insects.
Received: 18 July 1995/Accepted after revision: 1 October 1995 相似文献