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961.
Three strains of the chain-forming diatom Skeletonema marinoi, differing in their production of polyunsaturated aldehydes (PUA) and nutritional food components, were used in experiments
on feeding, egg production, hatching success, pellet production, and behavior of three common planktonic copepods: Acartia tonsa, Pseudocalanus elongatus, and Temora longicornis. The three different diatom strains (9B, 1G, and 7J) induced widely different effects on Acartia tonsa physiology, and the 9B strain induced different effects for the three copepods. In contrast, different strains induced no
or small alterations in the distribution, swimming behavior, and turning frequency of the copepods. 22:6(n-3) fatty acid (DHA)
and sterol content of the diet typically showed a positive effect on either egg production (A. tonsa) or hatching success (P. elongatus), while other measured compounds (PUA, other long-chain polyunsaturated fatty acids) of the algae had no obvious effects.
Our results demonstrate that differences between strains of a given diatom species can generate effects on copepod physiology,
which are as large as those induced by different algae species or groups. This emphasizes the need to identify the specific
characteristics of local diatoms together with the interacting effects of different mineral, biochemical, and toxic compounds
and their potential implications on different copepod species. 相似文献
962.
The assessment of relevant spatial scales at which ecological processes occur is of special importance for a thorough understanding
of ecosystem functioning. In coastal ecosystems, the variability of trophic interactions has been studied at different spatial
scales, but never at scales from centimetres to metres. In the present study, we investigated the link between habitat structure
and small-scale variability of food web functioning on intertidal boulder field ecosystems. Two microhabitats, boulder-top
and boulder-bottom, were considered, and the trophic ecology of invertebrate consumers was studied using stable isotope tracers.
We found for two of the main suspension feeders of northern Atlantic rocky shores (the sponges Halichondria panicea and Hymeniacidon sanguinea) consistent 15N enrichment for individuals sampled under boulders, suggesting that these consumers relied on different trophic resource
according to the microhabitat inhabited, at a centimetre scale. The high δ15N signatures found underneath boulders suggested higher use of highly decomposed organic matter in this microhabitat. The
isotopic difference between the two microhabitats decreased in higher trophic level consumers, which likely foraged at a spatial
scale including both microhabitats. Finally, our results reveal that in highly heterogeneous habitats such as boulder fields,
trophic interactions are likely to vary strongly in space, which should be considered in future researches. The link between
habitat physical structure and food web variability might also contribute to the high biological diversity characterizing
heterogeneous ecosystems. 相似文献
963.
To investigate the ability of elasmobranchs to distinguish between differing prey-type electric fields we examined the electroreceptive
foraging behaviour of a model species, Scyliorhinus canicula (small-spotted catshark). Catshark preferences were studied by behaviourally conditioning them to swim through narrow tunnels,
and on exit presenting them simultaneously with two different electric fields. Their subsequent choices of the following paired
options were recorded; (i) Two artificial electric fields (dipole electrodes) with different magnitude direct current (D.C.),
(ii) Two artificial electric fields, one D.C. and the other alternating current (A.C.), of the same magnitude, and (iii) similar
magnitude, natural and artificial D.C. electric fields associated with shore crabs and dipole electrodes respectively. We
found a highly significant preference for the stronger D.C. electric field and a less pronounced, but still significant, preference
for the A.C. electric field rather than the D.C. electric field. No preference was demonstrated between the artificial and
natural D.C. electric fields. The findings are discussed in relation to the animal’s diet and ecology and with regard to anthropogenic
sources of electric fields within their habitat. 相似文献
964.
965.
Spatial distribution and temporal variation of epibenthic assemblages of coralligenous biogenic rocky outcrops occurring in
the northern Adriatic Sea (45°04′–45°24′N; 12°23′–12°43′E) were investigated by photographic sampling from 2003 to 2006 at
12 randomly selected sites. The dominant reef-forming organisms were the encrusting calcareous algae (Lithophyllum stictaeforme, Lithothamnion minervae and Peyssonnelia polymorpha), while the main bioeroders were boring sponges (Cliona viridis, C. celata, C. thoosina, C. rhodensis, Piona vastifica) and the bivalve Gastrochaena dubia. Composition of the assemblages varied thorough years and among sites. Spatial heterogeneity, at local and regional scale,
prevailed over temporal variation. This variability was related both to the geo-morphological features of the outcrops and
to environmental variables. Sites clearly differed in the percent cover of reef builder and bioeroder species while only limited
temporal variation within site was found. Some taxa revealed complex intra-site temporal trends. These results provide valuable
information on the diversity and variability of epibenthic assemblages of the northern Adriatic coralligenous reefs, essential
for the management and conservation of these unique biogenic habitats. 相似文献
966.
Thomas Kneib Felix Knauer Helmut Küchenhoff 《Environmental and Ecological Statistics》2011,18(1):1-25
The investigation of animal habitat selection aims at the detection of selective usage of habitat types and the identification
of covariates influencing their selection. The results not only allow for a better understanding of the habitat selection
process but are also intended to help improve the conservation of animals. Usually, habitat selection by larger animals is
assessed by radio-tracking or visual observation studies, where the chosen habitat is determined for some animals at a set
of specific points in time. Hence the resulting data often have the following structure: a categorical variable indicating
the habitat type selected by an animal at a specific point in time is repeatedly observed and will be explained by covariates.
These may either describe properties of the habitat types currently available and/or properties of the animal. In this paper,
we present a general approach to the analysis of such data in a categorical regression setup. The proposed model generalizes
and improves upon several of the approaches previously discussed in the literature. In particular, it accounts for changing
habitat availability due to the movement of animals within the observation area. It incorporates both habitat- and animal-specific
covariates, and includes individual-specific random effects to account for correlations introduced by the repeated measurements
on single animals. Furthermore, the assumption that the effects are linear can be dropped by including the effects in nonparametric
manner based on a penalized spline approach. The methodology is implemented in a freely available software package. We demonstrate
the general applicability and the potential of the proposed approach in two case studies: The analysis of a songbird community
in South-America and a study on brown bears in Central Europe. 相似文献
967.
Orb web spiders of the genus Argiope are permanently located at the hub of the orb web and are thus vulnerable to changing environmental conditions. Severe damage
to the web by non-prey animals can have a significant impact on survival, through the cost of producing expensive silk and
the loss of foraging opportunities. Thus, selection should favor web protection mechanisms, and the conspicuous web decorations,
typical of Argiope spiders, may play a role. Decorated webs suffer less damage than undecorated webs, consistent with the view that they advertise
the presence of the web to non-prey animals that may damage the web. However, whether spiders respond to web damage by increasing
investment in web decorations has not been investigated. We subjected adult St. Andrew's Cross spider (Argiope keyserlingi) females to three levels of web damage and recorded their subsequent web-decorating behavior. Mild damage, similar to that
caused by impacting prey, did not affect either web building or decorating behavior. However, spiders subjected to substantial
web damage both reduced the size of subsequent webs and increased investment in web decoration size. These data are consistent
with an advertising role of web decorations. 相似文献
968.
Simon W. Townsend Markus Zöttl Marta B. Manser 《Behavioral ecology and sociobiology》2011,65(10):1927-1934
Socio-demographic factors, such as group size and their effect on predation vulnerability, have, in addition to intrinsic
factors, dominated as explanations when attempting to understand animal vigilance behaviour. It is generally assumed that
animals evaluate these external factors visually; however, many socially foraging species adopt a foraging technique that
directly compromises the visual system. In these instances, such species may instead rely more on the acoustical medium to
assess their relative risk and guide their subsequent anti-predator behaviour. We addressed this question in the socially
foraging meerkat (Suricata suricatta). Meerkats forage with their head down, but at the same time frequently produce close calls (‘Foraging’ close calls). Close
calls are also produced just after an individual has briefly scanned the surrounding environment for predators (‘Guarding’
close calls). Here, we firstly show that these Guarding and Foraging close call variants are in fact acoustically distinct
and secondly subjects are less vigilant (in terms of frequency and time) when exposed to Guarding close call playbacks than
when they hear Foraging close calls. We argue that this is the first evidence for socially foraging animals using the information
encoded within calls, the main adaptive function of which is unrelated to immediate predator encounters, to coordinate their
vigilance behaviour. In addition, these results provide new insights into the potential cognitive mechanisms underlying anti-predator
behaviour and suggest meerkats may be capable of signalling to group members the ‘absence’ of predatory threat. If we are
to fully understand the complexities underlying the coordination of animal anti-predator behaviour, we encourage future studies
to take these additional auditory and cognitive dimensions into account. 相似文献
969.
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
970.
Jonathan N. Pruitt Susan E. Riechert David J. Harris 《Behavioral ecology and sociobiology》2011,65(10):1957-1966
Relatively few investigations explicitly test for concordant versus conflicting selection pressures from intrasexual versus
intersexual selection. Here, we examine the effects of male body mass and behavioral type (BT) on reproductive success in
the spider Anelosimus studiosus, with emphasis placed on the potential interaction between intrasexual and intersexual selection influences. Female A. studiosus exhibit either an aggressive-active or docile-passive BT, both of which co-occur in multifemale colonies. Males, in contrast, exhibit a more continuous distribution of
behavioral tendencies. We investigated the male traits favored by females in five trial types: one docile female, one aggressive
female, four docile females, four aggressive females, and two docile and two aggressive females. Male reproductive success
was estimated by the number eggs produced by females following staged mating trials. In previous work, it was established
that large aggressive males are favored in male–male contests, an intrasexual effect. However, large aggressive males were
not universally favored here. We failed to detect an effect of male body mass or aggressiveness on reproductive success in
trials with all docile females; however, in situations involving aggressive females, large aggressive males experienced diminished
reproductive success relative to small docile males. Large, aggressive males were also more likely to be attacked and killed
by aggressive females in the first 20 min of staged encounters and were more likely to be found dead after 72 h of unobserved
interactions. Taken together, our data suggest that the reproductive consequences of male traits differ based on (1) the aspect
of sexual selection being considered (intrasexual versus intersexual) and (2) the BT of their prospective mates: large aggressive
males enjoy advantages in intrasexual selection and when courting docile females and small docile males experience reduced
risk of cannibalism and increased reproductive success with aggressive females. 相似文献