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71.
Habitat heterogeneity, structural complexity and habitat quality are key features of the environment that drive species' distribution and patterns of biological organization. Traditionally, pattern‐based studies have focused on faunal responses to biological systems. However, the influence of non‐biological environments such as insular rock outcrops on patterns of vertebrate distribution is conceivably as important, but has received less attention. Granite inselbergs are a naturally heterogeneous and spatially‐limited habitat. As such, they provide an opportunity for investigating whether environmental attributes influence social behaviour in animals that use these kinds of habitat, particularly lizards that are well adapted to saxicoline environments. We applied ecological theory to investigate the influence of habitat heterogeneity, structural complexity and habitat quality on patterns of home‐site occupancy in the crevice skink Egernia striolata (Lygosominea: Scincidae) from insular granite outcrops located within fragmented agricultural landscapes. We compared home‐site occupancy among solitary juveniles, solitary adults and lizard aggregations. We found significant differences in home‐site occupancy between aggregations and solitary lizard outcrop attributes measured at multiple spatial scales. The probability of a home‐site being occupied by an aggregation increased where large rock masses were present, on northern aspects near the core of the outcrop and in structurally variegated landscapes. Significantly more aggregations occupied home‐sites surrounded by high boulder cover and crevice microhabitat. We provide evidence that geophysical attributes of granite inselbergs and landscape context can influence patterns of lizard aggregation. Thus, we clearly document the environmental correlations of variability in sociality among subpopulations of Egernia striolata. 相似文献
72.
The murid rodent subfamily Sigmodontinae contains 79 genera which are
distributed throughout the New World. The time of arrival of the first
sigmodontines in South America and the estimated divergence time(s) of the
different lineages of South American sigmodontines have been controversial
due to the lack of a good fossil record and the immense number of extant
species. The "early-arrival hypothesis" states that the sigmodontines must
have arrived in South America no later than the early Miocene, at least 20
MYA, in order to account for their vast present-day diversity, whereas the
"late-arrival hypothesis" includes the sigmodontines as part of the
Plio-Pleistocene Great American Interchange, which occurred approximately
3.5 MYA. The phylogenetic relationships among 33 of these genera were
reconstructed using mitochondrial DNA (mtDNA) sequence data from the ND3,
ND4L, arginine tRNA, and ND4 genes, which we show to be evolving at the
same rate. A molecular clock was calibrated for these genes using published
fossil dates, and the genetic distances were estimated from the DNA
sequences in this study. The molecular clock was used to estimate the dates
of the South American sigmodontine origin and the main sigmodontine
radiation in order to evaluate the "early-" and "late-arrival" scenarios.
We estimate the time of the sigmodontine invasion of South America as
between approximately 5 and 9 MYA, supporting neither of the scenarios but
suggesting two possible models in which the invading lineage was either (1)
ancestral to the oryzomyines, akodonts, and phyllotines or (2) ancestral to
the akodonts and phyllotines and accompanied by the oryzomyines. The
sigmodontine invasion of South America provides an example of the advantage
afforded to a lineage by the fortuitous invasion of a previously
unexploited habitat, in this case an entire continent.
相似文献
73.
Aggregate data studies of disease risk factors 总被引:7,自引:0,他引:7
74.
Background
Host parasitism by Trichomonas vaginalis is complex. Adherence to vaginal epithelial cells (VECs) is mediated by surface proteins. We showed before that antisense down-regulation of expression of adhesin AP65 decreased amounts of protein, which lowered levels of T. vaginalis adherence to VECs. We now perform antisense down-regulation of expression of the ap33 gene to evaluate and confirm a role for AP33 in adherence by T. vaginalis. We also used an established transfection system for heterologous expression of AP33 in T. foetus as an additional confirmatory approach. 相似文献75.
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79.
The dinoflagellate alga Symbiodinium sp., living in symbiosis with corals, clams and other invertebrates, is a primary producer in coral reefs and other marine ecosystems. The function of the carbon‐fixing enzyme ribulose 1,5‐bisphosphate carboxylase/oxygenase (Rubisco) in dinoflagellates is difficult to study because its activity is rapidly lost after extraction from the cell. We report procedures for the extraction of Rubisco from Symbiodinium cells and for stable storage. We describe a continuous assay for Rubisco activity in these crude cell extracts using the Mn2+ chemiluminescence of Rubisco oxygenase. Chemiluminescence time courses exhibited initial transients resembling bacterial Form II Rubisco, followed by several minutes of linearly decreasing activity. The initial activity was determined from extrapolation of this linear section of the time course. The activity of fast‐frozen cell extracts was stable at ?80 °C and, after thawing and storage on ice, remained stable for up to 1 h before declining non‐linearly. Crude cell extracts bound [14C] 2‐carboxy‐D‐arabitinol 1,5‐bisphosphate to a high molecular mass fraction separable by gel filtration chromatography. After pre‐treatment of Symbiodinium cell cultures in darkness at temperatures above 30 °C, the extracted Rubisco activities decreased, with almost complete loss of activity above 36 °C. The implications for the sensitivity to elevated temperature of Symbiodinium photosynthesis are assessed. 相似文献
80.
Effects of elevated atmospheric CO2 on fine root length and distribution in an oak-palmetto scrub ecosystem in central Florida 总被引:1,自引:0,他引:1
FRANK P. DAY EVERETT P. WEBER C. ROSS HINKLE† BERT G. DRAKE‡ 《Global Change Biology》1996,2(2):143-148
Atmospheric CO2 concentration is rising and it has been suggested that a portion of the additional carbon is being sequestered in terrestrial vegetation and much of that in below-ground structures. The objective of the present study was to quantify the effects of elevated atmospheric CO2 on fine root length and distribution with depth with minirhizotrons in an open-top chamber experiment in an oak-palmetto scrub ecosystem at Kennedy Space Centre, Florida, USA. Observations were made five times over a period of one and a half years in three ambient chambers (350 p.p.m. CO2), three CO2 enriched chambers (700 p.p.m. CO2), and three unchambered plots. Greater root length densities were produced in the elevated CO2 chambers (14.2 mm cm?2) compared to the ambient chambers (8.7 mm cm?2). More roots may presumably lead to more efficient acquisition of resources. Fine root abundance varied significantly with soil depth, and there appeared to be enhanced proliferation of fine roots near the surface (0–12 cm) and at greater depth (49–61 cm) in the elevated CO2 chambers. The vertical root distribution pattern may be a response to availability of nutrients and water. More studies are needed to determine if increased root length under CO2 enriched conditions actually results in greater sequestering of carbon below ground. 相似文献