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471.
Bahía San Sebastián (BSS), a shallow and protected environment on the eastern coast of Tierra del Fuego (Argentina), is a
prime habitat for several species of nearctic migratory birds that visit the area during summer to feed in its huge intertidal
mudflats. The area has also great economic value due to the extraction and transport of hydrocarbons. Twenty-three dredge
stations were analysed and presence/absence data were used to classify stations and species by cluster analysis. Two algae
and 113 taxa of macrobenthic invertebrates from 12 animal phyla were identified. Species richness was one order of magnitude
higher (mean 29.0 sp st−1) in stations located outside or in the southern unprotected section of BSS than in most muddy or sandy stations within the
bay (mean 3.7 sp st−1). Hard bottom stations outside BSS were dominated by a rich assemblage of sessile filter-feeders, mainly bryozoans, hydrozoans,
ascidians, sponges, and the bivalve Aulacomya atra. Soft bottom areas inside BSS were mainly populated by relatively few species of deposit-feeders, such as the orbiniid polychaete
Phylo felix, which was particularly frequent and widespread. Shells of the clam Mulinia edulis are very common, representing one of the few hard substrata available for sessile species on soft bottoms. Epibenthic assemblages
within BSS were dominated by the detritivorous isopod Serolis paradoxa and the crab Eurypodius latreillei. The macrobenthic fauna of BSS can be regarded as typical of the Magellan region, showing affinities with those of other
localities around Tierra del Fuego, the Straits of Magellan and the southern Chilean fjords. 相似文献
472.
Odonates as Indicators of Shallow Lake Restoration by Liming: Comparing Adult and Larval Responses 总被引:4,自引:0,他引:4
F. D'Amico Stéphanie Darblade S. Avignon Stéphanie Blanc-Manel S. J. Ormerod 《Restoration Ecology》2004,12(3):439-446
Odonate assemblages were compared between replicate sets of shallow lakes that had been created and acidified by open‐cast mining across a large area (2,451 ha) of southwest France (Arjuzanx, Landes); one set of lakes (n = 5) was experimentally restored by liming with calcium carbonate, whereas another group (n = 5) was left as untreated reference lakes. Both odonate adults and exuviae were sampled bimonthly during May–August 1998. Elevated turbidity and conductivity in limed lakes were the only physicochemical measures differing between restored and reference lakes, because deacidification occurred naturally, even in reference lakes during the 17 years after the onset of restoration. Restoration by liming can apparently lead to effects on lake turbidity that might be considered adverse. Twenty‐four and 19 odonate species occurred among adults and exuviae, respectively, but there were no significant differences in richness between restored and reference sites. However, significantly, more exuviae were collected from the reference sites (588 vs. 180), where exuvial diversity and rank abundance indicated more evenly structured assemblages than those in restored lakes. Ordination showed that adult assemblages differed significantly between restored and reference lakes, and varied highly significantly with lake turbidity. This effect occurred because a small group of generally scarce adults were characteristic of reference sites (Chalcolestes viridis, Lestes virens, Cordulia aenae, Leucorrhinia albifrons, and Sympetrum sanguineum). Exuviae of these same species were less abundant at restored sites, but exuvial assemblages overall did not discriminate between restored and reference lakes. We conclude that lake restoration by liming can reduce diversity and larval numbers among odonates and subtly affects adult assemblages. In this case study, adult assemblages discriminated best between the lake types involved in the experiment, but important additional information arose from exuvial abundance and structure. This study indicates that natural recovery processes after acidification in formerly open‐cast areas––rather than chemical intervention through liming––might lead to preferable conservation outcomes. 相似文献
473.
474.
1. Most insect species occur at low abundance but a greater research effort has been devoted to so‐called outbreak species and little research is available on scarce (low abundance) species that are typical of most insect species. 2. Larval free‐feeding macrolepidoptera of two riparian trees Salix nigra (Marsh) (black willow) and Acer negundo L. (box elder) were sampled and sorted by species and abundance. 3. Data collected established that the majority of species in the assemblages in each tree species occurred at low abundance in each of the 5 years when larvae were sampled. 4. Species in the Noctuidae and Geometridae dominated both assemblages. 5. On both trees, assemblages were dominated numerically by relatively few species, a pattern that has been observed for insect assemblages on plants in managed and unmanaged habitats. 相似文献