Exotic plant invasions in an endemic‐rich habitat: The spread of an introduced Australian grass,Agrostis avenacea J. F. Gmel., in California vernal pools

Abstract The present abundance and historical spread of an exotic grass, Agrostis avenacea, is documented for California, USA, and for the vernal pools of San Diego County in particular. Agrostis avenacea is native to Australia where it is a common grass of ephemeral and fluctuating wetlands. California vernal pools, by reason of their extreme variability and high endemism, have been thought to be relatively resistant to invasion. The recent expansion of A. avenacea in San Diego County demonstrates, however, that the alleged resistance is probably a function of a relatively small pool of invaders and a low probability of targeted dispersal. Although A. avenacea is now abundant in pools with little current disturbance, human disturbance appears to have been a major factor that facilitated its initial establishment. This specific instance adds to the mounting evidence that there are probably few, if any, habitats immune to invasion.     

Gray Ukrainian cattle and their closely related forms

Data of previous investigations on the origin of Gray Ukrainian cattle and their relatives in European countries are duscussed. Literature data on the biodiversity of the exterior, phenotypic, and productive indices of ecotypes and breed groups of Gray Ukrainian cattle under various environmental and geographical conditions are reported, which are supplemented with our own experimental data on the differentiation of a number of genetic-biochemical systems of different groups of Gray Ukrainian cattle raised under various environmental and geographic conditions.     

Vicinism and mass effect

Abstract. The term vicinism (neighbourship), first published in a phytosociological context by Nordhagen, refers to the occurrence of plant species in a less favourable environment -outside their sociological (ecological) amplitude — as a result of the continuous supply of propagules from neighbouring areas. In recent studies on this subject the term mass effect has been used for what seems to be the same phenomenon. This is unfortunate since this term was introduced much earlier to indicate the ability of plants which are able to grow in dense stands in order to change the local environment to the benefit of themselves — physically, chemically or mechanically- by developing a dense vegetation cover. Examples of this mass effect are mainly found in extreme environments such as salt marshes and lake shores. The occurrence of both vicinism and mass effect indicates that competition is not the only biological factor important in selection. Vicinism also contributes to connectivity, a major topic in landscape ecology. Both vicinism and connectivity as synecological concepts in their original meaning deserve more attention from ecologists.