Recovery and resilience of tropical forests after disturbance

The time taken for forested tropical ecosystems to re-establish post-disturbance is of widespread interest. Yet to date there has been no comparative study across tropical biomes to determine rates of forest re-growth, and how they vary through space and time. Here we present results from a meta-analysis of palaeoecological records that use fossil pollen as a proxy for vegetation change over the past 20,000 years. A total of 283 forest disturbance and recovery events, reported in 71 studies, are identified across four tropical regions. Results indicate that forests in Central America and Africa generally recover faster from past disturbances than those in South America and Asia, as do forests exposed to natural large infrequent disturbances compared with post-climatic and human impacts. Results also demonstrate that increasing frequency of disturbance events at a site through time elevates recovery rates, indicating a degree of resilience in forests exposed to recurrent past disturbance

Too close for comfort: spatial patterns in acorn barnacle populations

Spatial patterns in aggregations form as a result of the interplay between costs and benefits experienced by individuals. Such self-organisation of aggregations can be explained using a zonal model in which a short-range zone of repulsion and longer-range zone of attraction surrounding individuals leads to emergent pattern properties. The signal of these processes can be detected using spatial pattern analyses. Furthermore, in sessile organisms, post-settlement mortality reveals the relative costs and benefits of positions within the aggregation. Acorn barnacles are known to require contact with conspecifics for reproduction and are therefore believed to aggregate for this purpose; isolated individuals may also be more susceptible to abiotic stress and predation. At short distances, however, competition for space and resources is likely to occur. In this study spatial patterns of barnacles (Semibalanus balanoides L.) were analysed using pair-correlation functions. Individuals were dispersed at distances below 0.30 cm, but peak relative density occurred at a distance of 0.36 cm from conspecifics. This is much closer than required for reproductive access, implying a strong aggregative drive, up to the point of physical contact with neighbours. Nevertheless, analysis of dead barnacles illustrated that such proximity carries a cost as barnacles with many neighbours were more likely to have died. The inferences obtained from these patterns are that barnacles aggregate as closely as they can, and that local neighbourhood competition is a powerful determinant of mortality. These processes give rise to the observed pattern properties

Palearctic predator invades North American Great Lakes

Bythotrephes cederstroemii Schoedler, a predatory freshwater zooplankter (Crustacea: Cladocera), was first found in the Laurentian Great Lakes in December 1984. The first individuals were from Lake Huron, followed in 1985 with records from Lakes Erie and Ontario. By late August, 1986 the species had spread to southern Lake Michigan (43°N). Bythotrephes has not previously been reported from North America, but has been restricted to a northern and central Palearctic distribution. Its dramatic and widespread rise in abundance in Lake Michigan was greatest in offshore regions. Bythotrephes appears to be invading aggressively, but avoiding habitats presently occupied by glacio-marine relict species that became established in deep oligotrophic North American lakes after the Wisconsin glaciation. Because it is a voracious predator its invasion may lead to alterations in the native zooplankton fauna of the Great Lakes. It offers the chance to study how invading plankton species join an existing community. Judging from its persistence and success in deep European lakes, Bythotrephes may now become a permanent member of zooplankton communities in the Nearctic.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47771/1/442_2004_Article_BF00378947.pd

Lead pollution resulting from Roman gold extraction in northwestern Spain

Roman mining and metallurgy left a detectable signal of lead pollution throughout Europe, northern Africa, and the Middle East. Las Médulas, in Northwestern Iberia, was the largest Roman gold mine and fundamentally altered the local landscape. To document the environmental consequences of this activity, we present a 4000-year record of lake sediment geochemistry from Laguna Roya, 35 km south of Las Médulas. Using the concentrations of trace metals weakly bound to sediment including lead, antimony, bismuth, and arsenic, we find increased levels of these metals from 300 BC to AD 120, during the Roman Republic/Empire. We attribute these increases to the atmospheric deposition of heavy metals arising from the regional extraction, processing, and/or smelting of gold ores. Lead pollution at the peak of this activity (15 BC) is twice as high as modern-day concentrations, suggesting that the amount of pollution generated by pre-Industrial civilizations and the associated environmental impacts are much larger than previously estimated. We find additional increases in antimony and bismuth from AD 1500 to 1700, possibly associated with post-medieval mining activity. Concentrations of lead begin to increase again ~AD 1860 during the start of the Industrial Revolution and reach a peak in AD 1990. Declining modern-day levels of lead can be attributed to the phase out of leaded gasoline. This is one of only a handful of studies to document pre-industrial pollution levels substantially higher than present-day, adding to a growing body of evidence that anthropogenic environmental degradation has been taking place for several thousands of years.Hewlett FoundationUniversity of Pittsburgh International Studies FundCSIC I-Link programMinisterio de Economía y Competitividad (España)US National Science FoundationDepto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasTRUEpu

Estadísticos poblacionales de Triatoma rubrovaria en condiciones de laboratorio Population statistics of Triatoma rubrovaria in laboratory

OBJETIVO: Obtener parámetros poblacionales de T. rubrovaria a fin de caracterizar demográficamente a esta especie. MÉTODOS: La investigación se realizó entre octubre de 2000 y febrero de 2003 en el laboratorio de artrópodos, Corrientes, Argentina. Se conformaron cinco cohortes de 100 huevos cada una. Los insectos se alimentaron sobre gallina (Gallus domesticus). Las cohortes se controlaron semanalmente. La experiencia se llevó a cabo en condiciones controladas de temperatura (28&plusmn;3ºC) y humedad relativa del aire (63&plusmn;10%). Se elaboraron tablas completas de vida y se obtuvieron estadísticos vitales. RESULTADOS: La mayor mortalidad se registró en ninfas de primero a cuarto estadio. A partir del quinto estadio el número de individuos decreció en forma constante. La expectativa de vida, después de superar las edades críticas, disminuyó en forma lineal. La supervivencia media de los adultos fue 50,2 semanas. La primera oviposición ocurrió a las 40,6 semanas. La fecundidad fue 859,6 huevos, con una media de 22,8 huevos. El período reproductivo fue de 37,7 semanas. El tiempo generacional fue de 55,3 semanas y la tasa neta de reproducción 133,7. La tasa intrínseca de incremento natural resultó 0,088. En una distribución estable de edades 25,3% correspondería al estado de huevo, 72,3% al estado ninfal y 2,4% al estado adulto. Los adultos contribuyeron con más del 70% al valor reproductivo total. CONCLUSIONES: Triatoma rubrovaria se caracterizó por una supervivencia prolongada como imago, una edad de la primera reproducción tardía y una tasa intrínseca de incremento natural baja.<br>OBJECTIVE: To obtain T. rubrovaria population parameters in order to describe its demographic characteristics. METHODS: The study was carried out in the laboratory of Arthropods, Corrientes, Argentina, from October 2000 to February 2003. Eggs were grouped to form five 100-egg cohorts. Insects were fed on chickens (Gallus domesticus). The cohorts were monitored weekly and kept under controlled temperature (28&plusmn;3&deg;C) and relative humidity (63&plusmn;10%). A life table was constructed and other vital statistics were calculated and recorded. RESULTS: Higher mortality was recorded in the first through the fourth nymphal stadium. A constant decrease was seen from the fifth nymphal instar. Life expectancy dropped linearly after overcoming the critical stages. Adults mean survival was 50.2 weeks. The first oviposition was after 40.6 weeks. The fecundity was 859.6 eggs with an average 22.8 eggs per female. The reproductive period was 37.7 weeks. The generation time was 55.3 weeks and the net reproduction rate was 133.7. The intrinsic rate of weekly increment was 0.088. In a stable age distribution the population would be composed of 25.3% eggs, 72.3% nymphs and 2.4% adults. Adults accounted for more than 70% of the total reproductive value. CONCLUSIONS: Triatoma rubrovaria had a long survival as imago, a late first reproduction and a low intrinsic rate of natural increase