11 research outputs found
Large-scale climatic phenomena drive fluctuations in macroinvertebrate assemblages in lowland tropical streams, Costa Rica: The importance of ENSO events in determining long-term (15y) patterns
Understanding how environmental variables influence the distribution and density of organisms over relatively long temporal scales is a central question in ecology given increased climatic variability (e.g., precipitation, ENSO events). The primary goal of our study was to evaluate long-term (15y time span) patterns of climate, as well as environmental parameters in two Neotropical streams in lowland Costa Rica, to assess potential effects on aquatic macroinvertebrates. We also examined the relative effects of an 8y whole-stream P-enrichment experiment on macroinvertebrate assemblages against the backdrop of this long-term study. Climate, environmental variables and macroinvertebrate samples were measured monthly for 7y and then quarterly for an additional 8y in each stream. Temporal patterns in climatic and environmental variables showed high variability over time, without clear inter-annual or intra-annual patterns. Macroinvertebrate richness and abundance decreased with increasing discharge and was positively related to the number of days since the last high discharge event. Findings show that fluctuations in stream physicochemistry and macroinvertebrate assemblage structure are ultimately the result of large-scale climatic phenomena, such as ENSO events, while the 8y P-enrichment did not appear to affect macroinvertebrates. Our study demonstrates that Neotropical lowland streams are highly dynamic and not as stable as is commonly presumed, with high intra- and inter-annual variability in environmental parameters that change the structure and composition of freshwater macroinvertebrate assemblages.This study was financed by National Science Foundation (DEB 1122389) to Catherine M. Pringle. The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.UCR::VicerrectorÃa de Investigación::Unidades de Investigación::Ciencias Básicas::Centro de Investigación en Ciencias del Mar y LimnologÃa (CIMAR
Understanding a migratory species in a changing world: climatic effects and demographic declines in the western monarch revealed by four decades of intensive monitoring
Migratory animals pose unique challenges for conservation biologists, and we have much to learn about how migratory species respond to drivers of global change. Research has cast doubt on the stability of the eastern monarch butterfly (Danaus plexippus) population in North America, but the western monarchs have not been as intensively examined. Using a Bayesian hierarchical model, sightings of western monarchs over approximately 40Â years were investigated using summer flight records from ten sites along an elevational transect in Northern California. Multiple weather variables were examined, including local and regional temperature and precipitation. Population trends from the ten focal sites and a subset of western overwintering sites were compared to summer and overwintering data from the eastern migration. Records showed western overwintering grounds and western breeding grounds had negative trends over time, with declines concentrated early in the breeding season, which were potentially more severe than in the eastern population. Temporal variation in the western monarch also appears to be largely independent of (uncorrelated with) the dynamics in the east. For our focal sites, warmer temperatures had positive effects during winter and spring, and precipitation had a positive effect during spring. These climatic associations add to our understanding of biotic-abiotic interactions in a migratory butterfly, but shifting climatic conditions do not explain the overall, long-term, negative population trajectory observed in our data
Eight years of monitoring aquatic Oligochaeta from the BaÃa and Ivinhema Rivers
The aim of this study was to analyze the factors that influence spatial and temporal variations of the Oligochaeta assemblage in the BaÃa and Ivinhema Rivers, located in the Upper Paraná River floodplain (Mato Grosso do Sul State, Brazil). Samples of Oligochaeta were collected between February 2000 and November 2007. A total of 27 Oligochaeta species were identified. A Principal Component Analysis (PCA) of the physical and chemical variables was used to summarize the total variation in the data and to identify major environmental gradients. Detrended Correspondence Analysis (DCA) was conducted to verify possible spatial and temporal gradients in the Oligochaeta species distribution. The highest Oligochaeta species densities and richness values were recorded during limnophases. The intensity and amplitude of the potamophase influenced the density, richness and composition of Oligochaeta since many species were transported by high water current velocities and/or died due to the low oxygen levels that are characteristic of this phase. L. hoffmeisteri, P. descolei and A. pigueti were recorded in the potamophase and in the limnophase and we concluded that they are adapted to different conditions of rivers (lotic and lentic) due to the presence of these species during the entire study period in both rivers. Nevertheless, these species were dominant in the potamophase periods of these rivers as they have body adaptations to survive in these conditions
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Support for global climate reorganization during the "Medieval Climate Anomaly"
Widely distributed proxy records indicate that
the Medieval Climate Anomaly (MCA; *900–1350 AD)
was characterized by coherent shifts in large-scale Northern
Hemisphere atmospheric circulation patterns. Although
cooler sea surface temperatures in the central and eastern
equatorial Pacific can explain some aspects of medieval
circulation changes, they are not sufficient to account for
other notable features, including widespread aridity
through the Eurasian sub-tropics, stronger winter westerlies
across the North Atlantic and Western Europe, and shifts in
monsoon rainfall patterns across Africa and South Asia.
We present results from a full-physics coupled climate
model showing that a slight warming of the tropical Indian
and western Pacific Oceans relative to the other tropical
ocean basins can induce a broad range of the medieval
circulation and climate changes indicated by proxy data,
including many of those not explained by a cooler tropical
Pacific alone. Important aspects of the results resemble
those from previous simulations examining the climatic
response to the rapid Indian Ocean warming during the late
twentieth century, and to results from climate warming
simulations—especially in indicating an expansion of the
Northern Hemisphere Hadley circulation. Notably, the
pattern of tropical Indo-Pacific sea surface temperature
(SST) change responsible for producing the proxy-model
similarity in our results agrees well with MCA-LIA SST
differences obtained in a recent proxy-based climate field
reconstruction. Though much remains unclear, our results
indicate that the MCA was characterized by an enhanced
zonal Indo-Pacific SST gradient with resulting changes in
Northern Hemisphere tropical and extra-tropical circulation
patterns and hydroclimate regimes, linkages that may
explain the coherent regional climate shifts indicated by
proxy records from across the planet. The findings provide
new perspectives on the nature and possible causes of the
MCA—a remarkable, yet incompletely understood episode
of Late Holocene climatic change