|Abstracts on Global Climate Change|
Photoreactivation in two freshwater ciliates: differential responses to variations in UV-B flux and temperature
Sanders, RW Macaluso, AL Sardina, TJ Mitchell, DL
AQUATIC MICROBIAL ECOLOGY 40:3 283-292
The effects of UV-B radiation on 2 ciliate species (Glaucoma sp. and Cyclidium sp.) from a clear oligotrophic lake were examined under laboratory conditions with and without photoreactivating radiation (PRR: UV-A and visible light). Glaucoma sp. was exposed to 3 UV-B intensities at 4 temperatures to simulate a range of environmentally relevant conditions. Population growth of Glaucoma sp. declined with increasing levels of UV-B exposure in treatments receiving PRR; blocking PRR generally resulted in 100% mortality. Occurrence of cyclobutane pyrimidine dimers (CPDs [mb DNA](-1)) was significantly reduced in Glaucoma sp. receiving PRR relative to those without PRR. These data indicate that photoenzymatic repair is a major component of UV-B tolerance in Glaucoma. At UV-B levels that Glaucoma sp. tolerated, Cyclidium sp. suffered 100% mortality and accumulated a similar level of CPDs whether or not PRR was blocked. Incubation of the 2 ciliates under UV-transparent and UV-blocking acrylics in the oligotrophic lake confirmed their relative sensitivities to UV radiation (UVR). Photoenzymatic repair in Glaucoma sp. was more efficient at 20 degrees C than at 10, 15 and 25 degrees C. The temperature-dependent nature of photoenzymatic repair underscores the need to consider the interactive effects of temperature and UVR on biota, particularly in the face of global climate change and rising incident UVR due to ozone depletion.
Derivation of quantitative management objectives for annual instream water temperatures in the Sabie River using a biological index
Rivers-Moore, NA Jewitt, GPW Weeks, DC
WATER SA 31:4 473-481
Adaptive management of river systems assumes uncertainty and makes provision for system variability. Inherent within this management approach is that perceived limits of ‘acceptable’ system variability are regarded not only as testable hypotheses, but also as playing a central role in maintaining biodiversity. While the Kruger National Park currently functions as a flagship conservation area in South Africa, projected increases in air temperatures as a consequence of global climate change present challenges in conserving this biodiversity inside the established land boundaries. Within the rivers of the Kruger National Park, a management goal of maintaining biodiversity requires a clearer understanding of system variability. One component of this is water temperature, an important water quality parameter defining the distribution patterns of aquatic organisms. In this study, Chiloglanis anoterus Crass (1960) (Pisces: Mochokidae) was selected as a biological indicator of changes in annual water temperatures within the Sabie River in the southern Kruger National Park. Relative abundances of C. anoterus were determined using standard electro-fishing surveys. The presence or absence of C. anoterus was linked to cumulative annual heat units using a logistic regression model, and a critical annual cumulative water temperature threshold estimated. A correlative relationship between this temperature threshold and a biological index using a C. anoterus condition factor provides river ecologists with a tool to assess ecologically significant warming trends in Sabie River water temperatures. A similar approach could be applied with relative ease to other Southern African river systems. Further testing of this hypothesis is suggested, as part of the adaptive management cycle.
Possible impact of urbanization on the thermal climate of some large cities in Mexico
ATMOSFERA 18:4 249-252
Urbanization has been the dominant demographic trend during the second half of the 20th century in Mexico. In 2000 there were 69 cities with more than 100,000 inhabitants of which 9 of them exceeded one million population, totalizing 53.4 million. Using time series of mean monthly temperature for about a dozen available stations, this paper sets out to examine temperature changes occurring during the late 20th century. Since it is well established that urban warming is mainly a nocturnal phenomenon minimum temperature series were selected after a test for homogeneity. Trend analysis was applied to the minimum temperature series and a linear regression coefficient was obtained. Tests of significance were performed. Most of the positive trends proved to be significant (>90%). Although temperature trend variability amongst the individual cities was large (from 0.02 degrees C/decade to 0.74 degrees C/decade) average temperature increase in large (>= 10(6) inhabitants) cities was (0.57 degrees C/decade) considerably higher than that corresponding to medium size urban centers where on the average temperature increase was 0.37 degrees C/decade. These temperature increases express not only the urbanization effect but also that due to global climate change (of the order of 0.07 degrees C/decade) and natural variability. In concluding it may be said that increasing urbanization in Mexico has originated a positive trend in urban temperatures which has implications for human comfort and health.
Alterations in the production and concentration of selected alkaloids as a function of rising atmospheric carbon dioxide and air temperature: implications for ethno-pharmacology
Ziska, LH Emche, SD Johnson, EL George, K Reed, DR Sicher, RC
GLOBAL CHANGE BIOLOGY 11:10 1798-1807
The influence of recent and projected changes in atmospheric carbon dioxide concentration [CO2] with and without concurrent increases in air temperature was determined with respect to growth characteristics and production of secondary compounds (alkaloids) in tobacco (Nicotiana tabacum L.) and jimson weed (Datura stramonium L.) over a ca. 50-day period. Rising [CO2] above that present at the beginning of the 20th century resulted in consistent, significant increases in leaf area, and above ground dry weight (both species), but decreased leaf area ratio (LAR) and specific leaf area (SLA) in jimson weed. Increased temperature resulted in earlier development and increased leaf area for both species, but increases in above ground final dry weight were observed only for jimson weed. The secondary compounds evaluated included the alkaloids, nicotine, atropine and scopolamine. These compounds are generally recognized as having impacts with respect to herbivory as well as human physiology. Rising [CO2] reduced the concentration of nicotine in tobacco; but had no effect on atropine, and increased the concentration of scopolamine in jimson weed. However, because of the stimulatory effect of [CO2] on growth, the amount of all three secondary compounds increased on a per plant basis in both species. Temperature per se had no effect on nicotine or scopolamine concentration, but significantly increased the concentration and amounts of atropine per plant. Overall, the underlying mechanism of CO2 induced changes in secondary compounds remains unclear; however, these data suggest that the increase in [CO2] and temperature associated with global climate change may have significant effects not only with respect to herbivory, but on the production of secondary compounds of pharmacological impact.
Influence of land use on plant community composition and diversity in Highland Sourveld grassland in the southern Drakensberg, South Africa
JOURNAL OF APPLIED ECOLOGY 42:5 975-988
1. Biodiversity conservation of grasslands in the face of transformation and global climate change will depend mainly on rangelands because of insufficient conservation areas in regions suited to agriculture. Transformed vegetation (pastures, crops and plantations) is not expected to conserve much biodiversity. This study examined the impact of land use on the plant diversity and community composition of the southern Drakensberg grasslands in South Africa, which are threatened with complete transformation to pastures, crops and plantations. 2. The main land uses in this high rainfall region are: ranching or dairy production under private tenure using indigenous grassland, pastures (Eragrostis curvula, kikuyu and ryegrass) and maize; plantation forestry; communal tenure (maize and rangelands); and conservation. 3. Plant diversity and composition were assessed using Whittaker plots. Transformed cover types were depauperate in species and ranged from kikuyu (1.4 species m(-2)) and ryegrass (2.9), to pine plantation (3.1), E. curvula pasture (3.1), commercial maize (3.2) and communal maize (7.8). With the exception of pine plantations, these communities supported mostly exotic (50 of 70 species) or ruderal indigenous species and made little contribution to plant species conservation. Abandoned communal cropland reverted to an indigenous grassland almost devoid of exotic species within c. 20 years. 4. It was predicted that frequently cultivated sites (maize and ryegrass) would support less diversity than long-lived pastures (kikuyu and E. curvula). This was contradicted by the relatively high species diversity of communal maize fields, which was attributed to a lack of herbicides, and the depauperate communities of kikuyu and of E. curvula pasture, which were attributed, respectively, to a dense growth form and a severe mowing regime. 5. Pine plantations harboured fourfold more indigenous species per plot (27) than other transformed types. Species were mostly shade-tolerant grassland relics that had persisted for 12 years since planting, and some forest colonizers. Indigenous species were unlikely to be maintained because of aggressive invasion by the exotic Rubus cuneifolius and severe disturbance associated with tree harvest and replanting. 6. The richness of indigenous grasslands was expected to differ in response to grazing pressure but they differed only in composition. Grasslands were dominated by grasses, despite the richness of herbaceous species. The dominance of Themeda triandra was reduced under livestock grazing in favour of more grazing-tolerant species. Exotic species were inconspicuous except for the dicotyledon Richardia brasiliensis, a subdominant under communal grazing. 7. Southern Drakensberg grasslands are probably now stocked with livestock six- to 35-fold higher than during pre-settlement times. A grassland protected for c. 50 years supported twofold greater richness (101 species plot(-1)) than grazed grasslands, suggesting that a 150-year history of increased mammalian grazing had already reduced plant diversity. 8. Synthesis and applications. Land acquisition is costly, thus conservation of plant diversity in the southern Drakensberg requires a policy that inhibits transformation of rangelands. This can be achieved by enhancing their economic viability without changing the vegetation composition. Their inherent value must be recognized, such as for water production. The viability of commercial ranches can be improved by increasing their size. Conservation efforts need to be focused on plant taxa that only occur on unprotected rangelands.