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     

Fire frequency influences composition and structure of the shrub layer in an Australian subcoastal temperate grassy woodland

Little is known about the relationship between fire regimes and plant diversity in Australia's temperate grassy woodlands. The effect of fire frequency on shrubs in grassy woodland remnants across Western Sydney's Cumberland Plain was examined. Shrub species richness and composition were compared in sites that had experienced a high, moderate or low frequency of fire over the previous 20 years. Nine sites were surveyed, three in each fire frequency category; most sites, including all low‐fire‐frequency sites, had burnt 9–36 months prior to sampling. Fire frequency had a profound effect on the composition and structure of the shrub layer. Per cent frequency and density of the prickly shrub Bursaria spinosa (Pittosporaceae) was considerably higher in low‐fire‐frequency sites than where fires had occurred at least once a decade. In sites where fire had been absent for decades prior to a recent fire, this species dominated the landscape, while elsewhere it occurred as clumps in a grassy matrix. Per cent frequency of other native shrubs, particularly obligate seeders, was greatest at moderate fire frequencies. Exotic shrubs were recorded most often where fire had been rare. While ordination clearly separated out the low‐fire‐frequency sites, complete separation between high‐ and moderate‐fire‐frequency blocks was not achieved. The increase in Bursaria in the absence of fire mirrors the encroachment of woody plants into a range of grassy ecosystems around the world. The sensitivity of obligate seeder species, many of them short‐lived legumes with fire‐cued seeds, to both very frequent and very infrequent fire shows the vulnerability of these species to extreme fire regimes, despite the safeguards conferred by hard‐seededness. Competition from Bursaria, as well as loss of viable seed in the soil, may have contributed to the low frequency of these species after a long inter‐fire interval.     

The distribution and abundance of barnacles in a mangrove forest

Abstract The grey mangrove tree, Avicennia marina, forms a hard substratum in an area otherwise dominated by soft-sediment. Various intertidal organisms attach to and move about on the trees. The abundant barnacles Elminius covenus, Hexaminius popeiana and Hexaminius foliorum live on a variety of substrata in mangrove forests. Their patterns of distribution and abundance were recorded and models proposed to explain these patterns. Densities of barnacles on bark, leaves and twigs of A. marina were estimated in a locality near Sydney. Elminius covenus were more abundant on bark than on leaves or twigs of A. marina. Hexaminius popeiana, although less abundant on bark than E. covenus, were not found on twigs or leaves. In contrast, H. foliorum were more abundant on twigs than leaves and were not found on the bark of A. marina. Densities of barnacles were greater in the seaward than in landward parts of the forest. Elminius covenus were the most abundant barnacles, H. foliorum were less abundant and H. popeiana were virtually absent in the landward zone. Barnacles in the seaward zone were most abundant at mid-tidal levels, less at high and low tidal levels of trunks and more abundant on lower than upper surfaces of trunks and leaves. The densities of barnacles differed according to the orientation of the bark or leaf. Models are proposed to explain the patterns of distribution and abundance of these barnacles. Each involves larval supply, settlement and post-settlement mortality. It is concluded that similar processes determining patterns of distribution and abundance for sessile organisms living on rock platforms may be applicable to sessile organisms living in the very different habitats of mangrove forests.     

Unconquered Lacandon Maya: Ethnohistory and Archaeology of Indigenous Change

Unconquered Lacandon Maya: Ethnohistory and Archaeology of Indigenous Change . Joel W. Palka. Gainesville: University Press of Florida, 2005. 319 pp.     

The role of avian ‘seed predators’ as seed dispersers

Seed dispersal is a central process in plant ecology with consequences for species composition and habitat structure. Some bird species are known to disperse the seeds they ingest, whereas others, termed ‘seed predators’, digest them and apparently play no part in dispersal, but it is not clear if these are discrete strategies or simply the ends of a continuum. We assessed dispersal effectiveness by combining analysis of faecal samples and bird density. The droppings of seed dispersers contained more entire seeds than those of typical seed predators, but over a quarter of the droppings of seed predators contained whole seeds. This effect was further magnified when bird density was taken into account, and was driven largely by one frequent interaction: the Chaffinch Fringilla coelebs, a typical seed predator and the most abundant bird species in the area and dispersed seeds of Leycesteria formosa, a non‐native plant with berry‐like fruits. These results suggest the existence of a continuum between seed predators and seed dispersers.