Showing papers on "Biotic component published in 1998"
TL;DR: The roles of physical factors and herbivory in structuring the early development of algal assemblages were investigated on a seasonal, tropical rocky shore in Hong Kong and exclusion of herbivores resulted in the developn~ent of ephemeral, erect algalassemblages.
Abstract: The roles of physical factors and herbivory in structuring the early development of algal assemblages were investigated on a seasonal, tropical rocky shore in Hong Kong. Physical stress was manipulated by irrigating areas with filtered seawater, whilst herbivore access was controlled using fences. Algal colonisation was monitored at 2 tidal heights (highand lowshore), once in the cool and dry season and once in the hot and wet season. Dry areas were only colonised in the lowshore and, even when herbivores were excluded, dry highshore areas never developed a macroalgal cover. Algal assemblages did, however, develop in highshore irrigated areas, where, in the presence of herbivores, encrusting algae (e.g. Hapalospongidion gel~tinosum and coralline crusts) developed. In areas excluding herbivores, ephemeral erect algae (e.g. Ulva spp.) developed. All lowshore treatments developed algal assemblages. In the hot season, after an initial phase of erect algae, encrusting algae developed where herbivores had access, whereas, in the cool season, erect Corallina spp. dominated these treatments In herbivore exclusions, erect ephemeral algae developed in the hot season with a sparse cover of encrusting algae (Ralfsia expansa and coralline crusts) whilst, in the cool season, a cover of Corallina spp. and erect ephemeral algae became abundant. When irrigation was terminated, erect algal cover decreased dramatically in each season in the highshore, although encrusting algae persisted at reduced cover. In lowshore areas, algal cover decreased marginally when irrigation was terminated and only during the hot season. The timing (i.e. hot or cool season) of liberation of rock space was, therefore, important for the development of algal assemblages. In lowshore areas, assemblages domlnated by encrusting algae typical of rocky shores in Hong Kong developed only in the presence of herbivores and only during the hot season. During the cool season. Corallina spp. became dominant, while exclusion of herbivores (during either season) resulted in the developn~ent of ephemeral, erect algal assemblages.
41 citations
TL;DR: Spatial heterogeneity of zooplankton biomass was found in both the horizontal and the vertical dimensions of the lake, and spatial patterns were quite similar for all size fractions.
Abstract: Although spatial heterogeneity of zooplankton has been explained by variations in abiotic and biotic factors as well as their cascading interactions, few studies have paid attention to the relative importance of these processes in structuring the vertical and horizontal distribution of zooplankton within a lake. The main objective of this study was to determine the relative importance of abiotic and biotic processes in the regulation of the vertical and horizontal distribution of four size fractions (53-100, 100-202, 202-500, and >500 µm) of the zooplankton biomass in a bog lake (Lake Geai, Quebec). Spatial heterogeneity of zooplankton biomass was found in both the horizontal and the vertical dimensions of the lake, and spatial patterns were quite similar for all size fractions. On the horizontal axis, spatial heterogeneity was stronger in the epilimnetic stratum. Zooplankton biomass was mainly aggregated in the east side of the lake in an area of higher conductivity and greater density of small chaoborid...
33 citations
Journal Article•
3 citations
1 Jan 1998
1 citations
1 Jan 1998
TL;DR: In this chapter, those factors responsible for creating stress are examined briefly and methods for producing material capable of withstanding its effects are outlined.
Abstract: In this chapter we shall examine briefly those factors responsible for creating stress (see Fig 8.1) and outline methods for producing material capable of withstanding its effects.
TL;DR: Spatial variation in the native fish community of the lower Guadiana basin (southern Iberia) was related to both biotic (abundance of exotic species) and environmental factors using canonical correspondence analysis, CCA.
Abstract: Spatial variation in the native fish community of the lower Guadiana basin (southern Iberia) was related to both biotic (abundance of exotic species) and environmental factors using canonical correspondence analysis, CCA. After choosing the best predictors among the environmental and biotic variables, we partitioned the total variation in native species abundances (18 species-size combinations by 44 sampling locations matrix) into that accounted for (1) solely by selected environmental variables, (2) solely by selected biotic variables, (3) by both environmental and biotic variables together, and (4) that unexplained. Of the 22 variables initially considered in the environmental CCA, only RIVER (dummy variable codifying sampling locations belonging to the main river), SALT (dummy variable codifying sampling locations belonging to tributaries that discharge to the brackish Guadiana), substrate heterogeneity, and macrobenthos abundance were selected as best predictors. In the biotic CCA, three species-size combinations were selected from the eight considered: Micropterus salmoides > 150 mm in total length (TL), Lepomis gibbosus > 100 mm in TL and Gambusia holbrooki. The total variation in the native fish community was partitioned into the following components: pure environmental (24.4%), pure biotic (12.4%), shared (9.2%) and unexplained (54.0%). There was a significant influence of exotic fish on native community variation after accounting for the effect of environmental factors.