The biology and ecology of the fishes of a small tropical stream

Many small species of fish are found in the stream/swamp systems that flow into Lake Victoria. One such system, in Uganda, was inhabited permanently by only one species, although others ran into the stream when it was flooded in the rainy seasons. Other fishes were confined to the lower reaches near the mouth, but never moved far upstream.
Studies on the biology of these fishes indicate that reproductive behaviour is generally confined to the rains in all species, the cyprinids using the system especially for breeding purposes at these times. Factors other than sexual state, such as feeding habits, vary little between fish from the river and those from the lake.
Experiments show that there is a change in the sexual state of the females of one species during the journey upriver, indicating the importance of this activity in the life cycle of the migratory fish.
The young of the cyprinids first appear in the up-river swamps. Here they grow, migrating to the river and moving downstream to enter the lake after periods of time that are characteristic for each species. This distinctiveness in timing was also found for the other fishes that inhabit the system, and it suggests that downstream migration is controlled by changes in the physiological state of the fish with age.     

Interactions between fungi,bacteria and beech leaves in a stream microcosm

Summary Immigration and colonization of isolates of naturally occurring stream bacteria and hyphomycetes on beech leaves were studied in a laboratory stream microcosm. Fungal spores were more successful immigrants, especially on new leaves, than bacteria, which were more repelled than attracted by the substrate. Fewer bacteria immigrated to older leaves than to new, and bacteria multiplied faster in water than on leaves. Fungi and bacteria showed synergistic relationships so that each group grew significantly faster in presence of the other group. If one considers, differences in immigration, colonization and synergism patterns, fungal mycelia doubled about 10 times faster than bacterial cells which might explain the dominance of fungi usually found on leaves in early decay. The individual fungal species could be assigned to one of three colonization groups; one of fugitive species, preceding a second group of species that grew from rarity to dominance, and a third group of very slow colonizers. The leachate was fractionated in different molecular size classes by gel chromatography, and the fraction around 2500D in the new leaf leachate was associated with a high concentration of polyphenols. High-pressure liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS) revealed the presence of 16 phenolic acids in the new leaf leachate at concentrations ranging from < 1 to 640 g l^–1. All fungi except the species with the slowest growth rate grew faster on leachate with the fraction around 2500D removed, and the density of bacteria was significantly reduced when pure stream water was supplemented with compounds from the same fraction.     

Cell-free biology: exploiting the interface between synthetic biology and synthetic chemistry

Just as synthetic organic chemistry once revolutionized the ability of chemists to build molecules (including those that did not exist in nature) following a basic set of design rules, cell-free synthetic biology is beginning to provide an improved toolbox and faster process for not only harnessing but also expanding the chemistry of life. At the interface between chemistry and biology, research in cell-free synthetic systems is proceeding in two different directions: using synthetic biology for synthetic chemistry and using synthetic chemistry to reprogram or mimic biology. In the coming years, the impact of advances inspired by these approaches will make possible the synthesis of nonbiological polymers having new backbone compositions, new chemical properties, new structures, and new functions.     

Interactions between stochastic and deterministic processes in stream fish community assembly

Synopsis Numerous studies have attempted to determine whether stream fish communities are structured primarily by deterministic or stochastic processes. Previous work has assumed that stream fish communities will show either persistence about an equilibrium because of strong density-dependent processes or random variation in structure as a result of environmental stochasticity. In a 10-year study of a California stream, fish community structure changed under the influence of storm-induced high discharge events that impacted recruitment. Species' relative abundances were altered as pre-recruitment stream discharges differentially influenced year-class strength among species with contrasting life histories. Simulation of stream fish community assembly under flow-driven recruitment variation indicates that community structure will vary depending on how particular high-flow events affect species' relative abundances and ongoing density-dependent processes, including competition and predation. Results suggest that stream fish communities are likely to show alternate states rather than a single persistent equilibrium. However, community assembly will not be random but will depend on situation-specific interactions between density-independent and density-dependent processes.     

Diversity-oriented synthesis: exploring the intersections between chemistry and biology

Diversity-oriented synthesis (DOS) is an emerging field involving the synthesis of combinatorial libraries of diverse small molecules for biological screening. Rather than being directed toward a single biological target, DOS libraries can be used to identify new ligands for a variety of targets. Several different strategies for library design have been developed to target the biologically relevant regions of chemical structure space. DOS has provided powerful probes to investigate biological mechanisms and also served as a new driving force for advancing synthetic organic chemistry.     

Fire and the chemistry of a South African mountain stream

The effects of a late-summer prescribed burn on the chemistry of a second-order mountain stream in the south-western Cape, South Africa, were investigated. Nitrate concentrations in stream water were significantly higher during the winter of the post-burn year. Increased concentrations of chloride, bicarbonate, polyphenols and potassium and decreased sodium concentrations were also recorded. Concentrations of ammonium, phosphate, calcium, magnesium, total dissolved solids and hydrogen ions were not significantly affected by the burn. Ionic export from the catchment was generally greater in the post-burn year. Apart from nitrate, however, values probably lie within the natural range of year-to-year variation. It is predicted that enhanced losses of nitrate will decrease progressively with the recovery of the vegetation and the re-establishment of soil/plant nutrient cycles. Atmospheric losses of nutrients in smoke were unquantified, but may be of more significance to site productivity than losses through surface runoff, which, in the case of nitrogen, appear to be compensated by precipitation inputs.     

Trematode communities in snails can indicate impact and recovery from hurricanes in a tropical coastal lagoon

In September 2002, Hurricane Isidore devastated the Yucatán Peninsula, Mexico. To understand its effects on the parasites of aquatic organisms, we analyzed long-term monthly population data of the horn snail Cerithidea pliculosa and its trematode communities in Celestún, Yucatán, Mexico before and after the hurricane (February 2001 to December 2009). Five trematode species occurred in the snail population: Mesostephanus appendiculatoides, Euhaplorchis californiensis, two species of the genus Renicola and one Heterophyidae gen. sp. Because these parasites use snails as first intermediate hosts, fishes as second intermediate hosts and birds as final hosts, their presence in snails depends on food webs. No snails were present at the sampled sites for 6 months after the hurricane. After snails recolonised the site, no trematodes were found in snails until 14 months after the hurricane. It took several years for snail and trematode populations to recover. Our results suggest that the increase in the occurrence of hurricanes predicted due to climate change can impact upon parasites with complex life cycles. However, both the snail populations and their parasite communities eventually reached numbers of individuals and species similar to those before the hurricane. Thus, the trematode parasites of snails can be useful indicators of coastal lagoon ecosystem degradation and recovery.     

Interactions between a stream caddisfly and the algae on its case: factors affecting algal quantity

1. Field experiments were conducted to examine interactions between larvae of the caddisfly Gumaga nigricula and the algae (primarily diatoms) located on their sand grain cases. Floating experimental enclosures were placed in sunlit pools of a California stream. Treatments applied to occupied cases, or to those from which caddisflies had been removed, included variations in grazer density, addition of nutrients, and modification of illumination using shade cloth. 2. Neither faecal-enriched agar in empty cases nor injections of faecal material into plugged cases affected case chlorophyll a concentration; injected nutrients (N and P), however, did increase chlorophyll a concentration. Faecal material may be nutrient poor, or nutrients may not be readily released. In addition, the relatively impermeable case wall may reduce the likelihood that nutrients from caddisflies reach the algae on the outer case surface. 3. Although a Gumaga larva may graze algae from its own case, grazing by conspecifics and the caddisfly Helicopsyche borealis causes a greater reduction in the chlorophyll a content of cases. 4. Chlorophyll a content of empty cases was decreased by experimental reduction of light. Because of shading associated with burrowing, chlorophyll a content of cases occupied by Gumaga was low and was unaffected by experimental light reduction. 5. Removal of Gumaga from its case results in rapid accrual of algae. Thus, the net effect of larval presence is to diminish the algal content of its case.     

Impact of landscape and corridor design on primates in a large-scale industrial tropical plantation landscape

Tropical plantations are rapidly expanding as a source of industrial wood. In Indonesia, such large-scale industrial plantations are generally made of large mono-specific blocks interspersed with natural forest remnants. The extent and biodiversity value of these remnants vary as laws and regulations on their design and management are either unclear, without solid scientific basis or left to the interpretation of private companies responsible for the plantations. Our study area comprises of three Acacia mangium plantations, which have on average 18% of their total area set aside from production and conserved as natural forests. These remnant natural forests may, if appropriately designed and managed, be used to mitigate the negative impact of plantations on biodiversity by providing some degree of connectivity with and between remaining natural forest patches (such as the Tesso Nilo conservation area). We sampled natural vegetation in one and primate diversity in all three plantation sector and examined patterns of primate species richness and abundance with relation to spatial arrangement and dimensions of conservation area, which has been set aside from plantation production. We demonstrate unambiguously the critical importance of a well-connected network of natural forest corridors in the plantation landscape to maintain primates and discuss the potential biodiversity value of natural forest remnants in broad-scale industrial landscapes.     

Relationships between landscape patterns and species richness of trees,shrubs and vines in a tropical forest

The present study aims to identify and characterize the relationships among landscape structure and plant diversity in a tropical landscape forest in Quintana Roo, Mexico. Total species richness as well as that of trees, shrubs and vines species were identified from 141 sampling quadrats (16,543 individuals sampled). Based on vegetation classes obtained from multi-spectral satellite image classification, I constructed plant diversity maps of the landscape under study using stratified kriging. I calculated the mean number of species in individual patches as the average values of kriging estimates inside of each patch. I then explored the relationships between landscape pattern metrics and the species richness of trees, shrubs and vines, as well as all groups combined using regression analysis. I employed Akaike Information Criterion (AIC) to select a set of candidate models. Based on akaike weights, I calculated model-averaged parameters. Results show that plant diversity of the patches depends on both the quality of the surrounding habitats and the proximity of surrounding patches (i.e., patch isolation).     

Hydrology and fish diversity of a North Queensland tropical stream

Abstract The diversity and distribution of fish and the hydrology of the Black-Alice River System, North Queensland, are described from a 2-year study (September 1972 to August 1974). Most physico-chemical parameters measured exhibited seasonal patterns which are influenced by rainfall and discharge. A total of forty-one species of fishes belonging to four groups: freshwater tolerant, saltwater tolerant, diadromous and sporadic, were recorded during the study. The diversity of fish species decreased with increasing distance from the mouth of the system. Fluctuations in total diversity (H') were due to variations in ‘species richness’ (D) rather than to equitability (E). The ability of the fish community to ‘recover’ its diversity and longitudinal distribution after a flood of above-average magnitude is demonstrated.     

Microbial degradation of petroleum hydrocarbons in a polluted tropical stream

Summary Crude oil degradation was observed in water samples from three sites along the course of a polluted stream in Lagos, Nigeria. Consistent increase and decrease in the total viable counts (TVCs) of indigenous organisms occurred in the test and control experiments, respectively. Enrichments of the water samples with crude oil resulted in the isolation of nine bacteria belonging to seven genera. A mixed culture was developed from the assemblage of the nine species. The defined microbial consortium utilized a wide range of pure HCs including cycloalkane and aromatic HCs. Utilization of crude oil and petroleum cuts, i.e., kerosene and diesel resulted in an increase in TVC (till day 10) concomitant with decreases in pH and residual oil concentration. Crude oil, diesel and kerosene were degraded by 88, 85 and 78%, respectively, in 14 days. Substrate uptake studies with axenic cultures showed that growth was not sustainable on either cyclohexane or aromatics while degradation of the petroleum fractions fell below 67% in spite of extended incubation period (20 day). From the GC analysis of recovered oil, while reductions in peaks of n-alkane fractions and in biomarkers namely n-C₁₇/pristane and n-C₁₈/phytane ratios were observed in culture fluids of pure strains, complete removal of all the HC components of kerosene, diesel and crude oil including the isoprenoids was obtained with the consortium within 14 days.     

Growth and photosynthetic response of nine tropical species with long-term exposure to elevated carbon dioxide

Summary Seedlings of nine tropical species varying in growth and carbon metabolism were exposed to twice the current atmospheric level of CO₂ for a 3 month period on Barro Colorado Island, Panama. A doubling of the CO₂ concentration resulted in increases in photosynthesis and greater water use efficiency (WUE) for all species possessing C₃ metabolism, when compared to the ambient condition. No desensitization of photosynthesis to increased CO₂ was observed during the 3 month period. Significant increases in total plant dry weight were also noted for 4 out of the 5 C₃ species tested and in one CAM species, Aechmea magdalenae at high CO₂. In contrast, no significant increases in either photosynthesis or total plant dry weight were noted for the C₄ grass, Paspallum conjugatum. Increases in the apparent quantum efficiency (AQE) for all C₃ species suggest that elevated CO₂ may increase photosynthetic rate relative to ambient CO₂ over a wide range of light conditions. The response of CO₂ assimilation to internal C_i suggested a reduction in either the RuBP and/or Pi regeneration limitation with long term exposure to elevated CO₂. This experiment suggests that: (1) a global rise in CO₂ may have significant effects on photosynthesis and productivity in a wide variety of tropical species, and (2) increases in productivity and photosynthesis may be related to physiological adaptation(s) to increased CO₂.     

Long-term trends in soil solution and stream water chemistry at the Hubbard Brook Experimental Forest: relationship with landscape position

In acid-sensitive watersheds of the northeastern US, decreases in SO₂ emissions and atmospheric deposition of sulfur have not been accompanied by marked changes in pH and acid neutralizing capacity (ANC). To better understand this phenomenon, we investigated the long-term trends in soil solution (1984–1998) and stream water (1982–2000) chemistry along a natural soil catena at the Hubbard Brook Experimental Forest, New Hampshire, USA. Significant declines in strong acid anion concentrations were accompanied by declines in base cation concentrations in soil solutions draining the Oa and Bs soil horizons at all elevations. The magnitude of change varied with position in the landscape. Recovery, as indicated by increasing ANC (mean 2.38µEqL^–1year^–1) and decreasing concentrations of inorganic monomeric Al (mean 1.03µmolL^–1year^–1), was confined to solutions draining the Bs horizon at mid-to-higher elevations. However, persistently low Ca²⁺/Al_i ratios (<1) in Bs soil solutions at these sites may be evidence of continuing Al stress to trees. In Bs soil solution at a lower elevation site and in Oa soil solutions at all sites, declines in base cations (mean 3.71µEqL^–1year^–1) were either similar to or exceeded declines in strong acid anions (mean 3.25µEqL^–1year^–1) resulting in no change in ANC. Changes in the chemistry of stream water reflected changes in soil solutions, with the greatest improvement in ANC occurring at high elevation and the rate of increase decreasing with decreases in elevation. The pH of soil solutions and stream waters either declined or did not change significantly. Therefore pH-buffering processes, including hydrolysis of Al and possibly the deprotonation of organic acids, have prevented increases in drainage water pH despite considerable reductions in inputs of strong acids.     

Richness and abundance of stream fish communities in a fragmented neotropical landscape

Environmental Biology of Fishes - Environmental conditions influence ecological processes that shape stream community diversity and abundance. Deforestation has the potential to limit available...