Morphology and Life History of Colpoda maupasi, Bensonhurst Strain

Strains of Colpoda maupasi previously reported were found to produce only octogenic reproductive cysts and monogenic wrinkled resting cysts. The present form of C. maupasi (Bensonhurst strain), isolated by the senior author in 1949, was found to produce, in addition to the above, quadrigenic reproductive cysts, digenic corrugated (wrinkled) resting cysts, and smooth thick-walled monogenic, digenic and quadrigenic resting cysts. Some of the factors leading to the development of these cysts in the Bensonhurst strain are believed to be related to nutrition, age and size of the trophic forms. The cytological changes in encystment and excystment were followed with particular attention to aging monogenic resting cysts. The latter were observed for over 4 years.     

The savanna ecology of Kidepo Valley National Park: The effects of burning and browsing on the vegetation

Between 1947 and 1967 tree frequency was reduced by 30% in the Narus valley, Kidepo Valley National Park. Between 1967 and 1972 a further 50% reduction took place on experimental plots. Elephants were largely responsible. Despite a regeneration potential of c. 200 young trees per ha, very little tree regeneration was observed. Experimental fire treatments and animal–free exclosures revealed that annual burning and the current browsing pressure were independently capable of preventing tree regeneration. Fire effects were significant in the herb composition of the animal exclosures but less so on the grazed areas. This was attributed to trampling of litter on the grazed areas, which assisted termites in litter removal. Untrampled litter accumulation suppressed Themeda triandra to the benefit of Panicum maximum. Fire effects on the soil were small and impermanent.     

Oysters as habitat for limpets in a temperate mangrove forest

In temperate mangrove forests in New South Wales, Australia, the limpet Patelloida mimula Iredale lives on the oyster Saccostrea commercialis Iredale and Roughley, which, along with mangrove trees, provide the only hard substrata in a habitat otherwise dominated by soft-sediment. The objective of this study was to ascertain the degree of association between the limpet and the oyster by examining their patterns of co-occurrence in the forest and the relationship between individual pairs of limpets and oysters. Sampling of the distribution and abundance of limpets and oysters throughout the mangrove forest revealed that limpets were rarely present on substrata other than oysters. Patterns of abundance of limpets were, however, not directly related to the amount of habitat provided by the oysters. For example, there was a dramatic decline in the abundance of oysters from seaward to landward in the mangrove forest which was not reflected in the densities of limpets. Consequently, oysters appear to set the limits of distribution of limpets, but other factors modify their broad-scale patterns of distribution and abundance within these bounds. Limpets leave scars on oysters which might be home sites. About 98% of oysters with limpets had only one limpet per surface of oyster, and the distribution of limpets was overdispersed or repulsed. Moreover, in some areas of the forest, the lengths of limpets were directly related to lengths of oysters. Tracking of individual limpets for 13 days revealed that > 70% remained on the same scar of an oyster. This evidence suggests that for some limpets there is a strong association with particular oysters. Factors determining the distribution, abundance, and sizes of oysters are likely to be important sources of variation to the structure of populations of P. mimula in temperate mangrove forests.     

THE EFFECTS OF MECHANICAL DISTURBANCES ON THE BEHAVIOUR OF INACTIVE TERRESTRIAL SNAILS

Based on comparison to controls, inactive Otala lactea (Mull.)respond to mechanical disturbances such as shaking, percussion,transmitted vibrations, and rotation. Responses in a 15-minperiod include motion of large portions of the mantle, openingof the pneumostome and protrusion of the posterior part of thefoot through the mantle collar. Responses reflect preliminarystages of arousal. It is suggested that an incomplete arousalto a potentially valuable, but environmentally ambiguous stimulus,may be of adaptive value. (Received 30 January 1978;     

Lipid Mobilization During Dormancy Breakage in Oilseed of Corylus avellana

During the stratification necessary for the alleviation of dormancyin Corylus avellana L. there is a substantial reorganizationof metabolic processes. Changes in activities of some enzymesrelated to lipid mobilization were followed throughout a fruitstratification period at 5 °C and control treatment at 20°C. Significant increases in total lipase and isocitratelyase activities were found in both embryonic axes and cotyledonsof seeds from fruits stratified at 5 °C, whereas the activitiesremained consistently low in those held at 20 °C. Theseresults correlated with an earlier ultrastructural study whichshowed a reduction in storage lipid. The increased potentialfor lipolysis was concomitant with loss of dormancy as seenin germination tests. These findings suggest that lipid mobilizationduring stratification could be related to the overall patternof metabolic changes which are required for dormancy release. Corylus avellana L., hazel, lipid, catalase, isocitrate lyase, lipase, stratification     

Shredder–tadpole facilitation of leaf litter decomposition in a tropical stream

1. Leaf litter decomposition is one of the most important ecosystem processes in streams. Recent studies suggest that facilitation, in which litter is processed by a succession of species with differing abilities and requirements, may be important in making the nutrients bound in litter available to the stream assemblage.
2. We predicted that stream invertebrates that feed on terrestrial leaf litter (shredders) and tadpoles would facilitate leaf litter decomposition by changing the quality of leaf material directly via physical contact or indirectly via nutrient release. We experimentally examined the ability of shredders and tadpoles to break down leaves, independently and together, in artificial streams beside a natural forest stream.
3. The decomposition rate was greater when shredders and tadpoles were together than was expected from rates in single-species treatments, indicating that facilitation occurred. This facilitation operated in one direction only: the rate of leaf breakdown by tadpoles was higher when leaves had been partly processed by shredders, but there was no similar effect when leaves previously occupied by tadpoles were processed by shredders. We did not detect facilitation caused by indirect nutrient release.
4. Shredders may have benefited tadpoles by roughening leaf surfaces, making them easier for the tadpoles to consume and enhancing leaf breakdown in the presence of both taxa. This indicates that the loss of a single species can have impacts on ecosystem functioning that go beyond the loss of its direct contribution.