Evolution and the Ecosystem

Long-range stability in natural communities is mediated throughavenues of communication. One of the most important pathwaysof communication involves nutrient exchange, although othertypes of communication are suspected as being of considerableimportance. The potential role of special "regulator species"in community stabilization is discussed and illustrated withtwo original examples, one dealing with brackish-water communitiesof the North Carolina coast, and the other dealing with communitiesof the piedmont streams of eastern Mexico. The significanceof multi-species groups in evolution is also considered in thesecond example. It is suggested that the functional ecosystemis the fundamental seleclional unit of evolution and that evolutionproceeds by mutual adjustment of ecological entities into harmonioussystems with some degree ot permanence.     

A model for estimating infection levels of anthracnose disease of mango

Anthracnose disease of mango caused by Colletotrichum gloeosporioides var. minor, spreads by water-borne conidia from vegetative parts of the tree to attack inflorescences and prevent fruit set. An analysis of data from laboratory studies demonstrated that infection by conidia during wet periods was related both to the temperature and to the duration of the wet period. A model was used to estimate infection levels of anthracnose disease in two mango orchards over three seasons. The number of infection periods recorded and the estimated percentage of conidia forming appressoria in these periods matched disease development during flush growth and flowering. In 1980, only two infection periods were detected during flowering in one of these orchards and blossom blight did not prevent fruit set. In 1981 and 1982 however, higher estimated levels of infection were recorded more frequently during the same time and severe blossom blight developed. A second orchard, situated in an area less favourable to disease, was also monitored during 1982. Nine infection periods were recorded during flowering in this orchard compared to 14 in the first. A moderate level of blossom blight developed in this orchard.     

A comparison of spatially explicit landscape representation methods and their relationship to stream condition

1. Biodiversity, water quality and ecosystem processes in streams are known to be influenced by the terrestrial landscape over a range of spatial and temporal scales. Lumped attributes (i.e. per cent land use) are often used to characterise the condition of the catchment; however, they are not spatially explicit and do not account for the disproportionate influence of land located near the stream or connected by overland flow. 2. We compared seven landscape representation metrics to determine whether accounting for the spatial proximity and hydrological effects of land use can be used to account for additional variability in indicators of stream ecosystem health. The landscape metrics included the following: a lumped metric, four inverse‐distance‐weighted (IDW) metrics based on distance to the stream or survey site and two modified IDW metrics that also accounted for the level of hydrologic activity (HA‐IDW). Ecosystem health data were obtained from the Ecological Health Monitoring Programme in Southeast Queensland, Australia and included measures of fish, invertebrates, physicochemistry and nutrients collected during two seasons over 4 years. Linear models were fitted to the stream indicators and landscape metrics, by season, and compared using an information‐theoretic approach. 3. Although no single metric was most suitable for modelling all stream indicators, lumped metrics rarely performed as well as other metric types. Metrics based on proximity to the stream (IDW and HA‐IDW) were more suitable for modelling fish indicators, while the HA‐IDW metric based on proximity to the survey site generally outperformed others for invertebrates, irrespective of season. There was consistent support for metrics based on proximity to the survey site (IDW or HA‐IDW) for all physicochemical indicators during the dry season, while a HA‐IDW metric based on proximity to the stream was suitable for five of the six physicochemical indicators in the post‐wet season. Only one nutrient indicator was tested and results showed that catchment area had a significant effect on the relationship between land use metrics and algal stable isotope ratios in both seasons. 4. Spatially explicit methods of landscape representation can clearly improve the predictive ability of many empirical models currently used to study the relationship between landscape, habitat and stream condition. A comparison of different metrics may provide clues about causal pathways and mechanistic processes behind correlative relationships and could be used to target restoration efforts strategically.     

Presence of Cell and Virus Specific Sequences in the Same Molecules of Nuclear RNA from Virus Transformed Cells

Hybridization studies show that nuclear RNA in transformed cells contains both host and virus specific sequences. This suggests virus-specific mRNA could be formed by selective cleavage of high molecular weight nuclear RNA.     

Mapping of the Biological Resources of the Continental Shelf

Distribution patterns of the penaeid shrimp and demersal fishspecies are discussed based upon collections totaling in excessof 330,000 shrimp and 2,245,000 fishes. Depth related zonationreveals nearshore, mid-shelf, outer shelf, and trans-shelf assemblages.Estuary related species are particularly prominent on the northwesternGulf shelf, while rock and reef related species are most importantin the fauna of the eastern Gulf shelf. Recognizable elementsin the shelf fauna also include species of tropical affinity;open ocean and upper slope species; inhabitants of seagrassbeds, mangrove swamps, and carbonate rubble and shell hash;burrowers in soft bottoms; and inhabitants of the upper watercolumn. The eastern Gulf shelf is inhabited by twice as manyfish species and eight times as many unique species as the northwesternshelf, reflecting the great diversity of habitat types in theeastern Gulf. A few key species numerically dominate the ichthyofaunaof the northwestern shelf, but dominance is spread through manyspecies in the east. Seasonal shifts in species density primarilyreflect inshore/offshore seasonal migrations of estuary relatedspecies, but seasonal inshore/offshore density shifts are alsoobserved among the true shelf residents. Trophically the shelfsystems are supported by precipitated plankton and organic detritusderived from rivers, bays and estuaries, seagrass beds, andmangrove swamps, although attached algae are also importantproducers in the east. Mollusks, polychaetes, and small crustaceanswhich feed upon this material, in turn, support the demersalfish communities whose species are generally short-lived. Largerlonglived predators are mostly seasonal migrants which appearin the northern Gulf during the warmer months. Bottom-feedinggeneralists are prominent in the northwest, while specialistsare in great evidence in the east. These distributional studieslay the foundation for understanding the shelf ecological systems,and they also provide a basis for informed management decisions.