Community response to experimental soil disturbance in a midsuccessional,abandoned pasture

To determine whether soil disturbance by digging and burrowing mammals altered community structure and the rate of succession in a midsuccessional abandoned pasture, species richness, composition and relative abundance were monitored over a two year period both on and off artificially created earth mounds (100, 900, 8100 cm²). Mean species richness increased by up to two species per small mound (100 cm²) and by up to four species per large mound (8100 cm²). However, increased species richness was evident for less than two years. Initially, up to sixteen of the twenty species present occurred more often on earth mounds than off mounds, with two of these species found only on large mounds (8100 cm²). After two years, there was little or no significant difference in species composition and relative frequency on and off earth mounds. Experimental soil disturbance temporarily altered community structure simply by increasing space available for colonization since light, nutrient and water supply did not increase significantly on mounds. Soil disturbance can increase species richness and change species' relative frequency in disturbances as small as 100 cm² but such changes were likely too small and short lived to alter permanently the structure and rate of succession in the abandoned pasture studied here.     

Edaphic factors and plant species distribution in a protected area in the desert of Bahrain Island

Effects of edaphic factors (salinity, pH, Na⁺, K⁺, Ca⁺⁺, CaCO₃, water holding capacity, and grain size) on the spatial distribution of plants were investigated. Soil was sampled at 22 stands. Sixteen plant species were recorded from these stands. Relation between edaphic factors and plant distribution was investigated using correlation statistical analysis. Distribution of some plants was found to be highly correlated with edaphic factor(s).     

Spoil characteristics and vegetation development of an age series of mine spoils in a dry tropical environment

A series of coal mine spoils (5, 10, 12, 16 and 20-yr old) in a dry tropical environment was sampled to assess the changes with time in spoil characteristics, species composition and plant biomass. Coarse fragments (>2 mm) decreased with age of mine spoil while the proportion of 0.2–0.1 mm particles increased. Total soil N, mineral N, NaHCO₃-extractable Pi, and exchangeable K increased with age of mine spoil and these parameters were lower in mine spoils than native forest soil even after 20 years of succession. Exchangeable Na decreased with age of mine spoil and in 20-yr old spoil it was higher than native forest soil. Plant community composition changed with age. Only a few species participated in community formation. Species richness increased with age, while evenness and species diversity declined from 5-yr old to 16-yr old community with an increase in the 20-yr old community. A reverse trend occurred for concentration of dominance. Area-weighted shoot and root biomass of other species increased with the age of the mine spoil while that of Xanthium strumarium patches declined with age. Data collected on spoil features, microbial C, N and P, and shoot and root biomass when subjected to Discriminant Analysis indicated a continued profound effect of age. 10 and 12-yr old mine spoils were closer to each other, and 5 and 20-yr old spoils were farthest apart.     

Competitive exclusion,or species aggregation?

Summary There is a long-standing dispute over whether the analysis of species co-occurrence data, typically on islands in an archipelago, can disclose the forces at work in structuring a community. Here we present and utilise three scores S, C and T. S gives the mean number of islands shared by a species pair in the presence/absence data under study. The scores C and T are based on the way that a pair of species occurs on a pair of islands. When each species occurs on a different island, this adds to the checkerboard score C; if they occupy the same island, this increases the togetherness score T.In judging whether observed values of S, C and T are compatible with a null hypothesis assuming no species interaction, we follow Connor and Simberloff (1979) in generating a control group of (constrained) simulated incidence patterns.Presence/absence matrices can have paradoxical features, in combining a high mutual exclusion by species (checkerboardedness) with a degree of species aggregation that is also high. We show that this is in fact inevitable — that, given the usual contraints, C and T can differ only by a constant. This means that extreme checkerboardedness can be produced by forces making for species aggregation, just as well as by those making for avoidance.If we restrict our attention to a subset of species, the constraints are less rigid and the S, C and T scores are somewhat freer to vary. We consider the confamilial subsets in the Vanuatu archipelago as likely candidates for revealing any competition forces at work. Calculating the actual S, C and T scores for these subsets, we compare them with the corresponding scores in a sample of simulated colonization patterns.The actual species-distributions differ significantly from what we would expect if the colonization choices of different species were uncorrelated (save for some biological constraints). The confamilial species of the real world share more islands, and occur in a pattern less checkerboarded, and more aggregated, than their simulation counterparts. This suggests that competition pressures, if they exist, are overcome by countervailing factors.The method used is applicable in other ways, and to a wider class of problems, in analysing the forces behind community structure.     

The role of the hemiparasitic annual Rhinanthus minor in determining grassland community structure

Summary Rhinanthus minor (yellow-rattle) is a widespread hemiparasitic plant of grassland habitats throughout Great Britain. It is usually considered to be indicative of species-rich grassland, but in a survey of 14 habitats throughout Britain it was found that R. minor at the time of flowering normally occupied relatively low-diversity patches within areas of high diversity as determined by the number of species, Simpson's Index and the Shannon-Wiener Index. Following the death of adult plants of R. minor in the summer it was shown that the pattern of species diversity changed such that by the time R. minor germinated in the following spring the differences between the areas containing and not containing R. minor were much less distinct. A perturbation experiment in which R. minor was removed from four sites indicated that the effect of the removal of R. minor on the development of community structure over the next year was to increase species diversity on three of the sites and decrease it on the fourth. Those species which responded to the removal of R. minor by an increase in abundance were shown to be preferred hosts. All three lines of evidence point to the fact R. minor has a significant effect on the species diversity of the communities in which it grows by selectively parasitizing components of the flora and modifying the competitive relationships between plants. However, as the communities generally responded to the removal of R. minor by an increase in diversity and as the general survey indicated that R. minor is generally associated with areas of low diversity it would appear that the plants which are selectively parasitized are generally not the competitive dominants in the community.     

Outcrossing and hybridization in wild and cultivated foxtail millets: consequences for the release of transgenic crops

Summary Outcrossing rates within the wild green foxtail, Setaria viridis, and the cultivated foxtail millet, S. italica, are very low. However, spontaneous interspecific hybridizations in the experimental garden occurred in both directions at rates ranging from 0.002% to 0.6% according to plant density and distance between parents. Offtypes found in farmers' fields where foxtail millet is cultivated were shown to have originated from such interspecific crosses. Differences in the EcoR1 patterns of chloroplast DNA between cultivated and wild plants indicated that reciprocal crosses do occur in the field. These findings indicate that even a largely selfing cultivated species may exchange genetic information with wild relatives at rates that may cause problems if transgenic cultivars are released.     

Evolutionary theory and systematics: relationships between process and patterns

The relevance of the Modern Evolutionary Synthesis to the foundations of taxonomy (the construction of groups, both taxa and phyla) is reexamined. The nondimensional biological species concept, and not the multidimensional, taxonomic, species notion which is based on it, represents a culmination of an evolutionary understanding. It demonstrates how established evolutionary mechanisms acting on populations of sexually reproducing organisms provide the testable ontological basis of the species category. We question the ontology and epistemology of the phylogenetic or evolutionary species concept, and find it to be a fundamentally untenable one. We argue that at best, the phylogenetic species is a taxonomic species notion which is not a theoretical concept, and therefore should not serve as foundation for taxonomic theory in general, phylogenetics, and macroevolutionary reconstruction in particular. Although both evolutionary systematists and cladists are phylogeneticists, the reconstruction of the history of life is fundamentally different in these two approaches. We maintain that all method, including taxonomic ones, must fall out of well corroborated theory. In the case of taxonomic methodology the theoretical base must be evolutionary. The axiomatic assumptions that all phena, living and fossil, must be holophyletic taxa (species, and above), resulting from splitting events, and subsequently that evaluation of evolutionary change must be based on a taxic perspective codified by the Hennig ian taxonomic species notion, are not testable premises. We discuss the relationship between some biologically, and therefore taxonomically, significant patterns in nature, and the process dependence of these patterns. Process-free establishment of deductively tested “genealogies” is a contradiction in terms; it is impossible to “recover” phylogenetic patterns without the investment of causal and processual explanations of characters to establish well tested taxonomic properties of these (such as homologies, apomorphies, synapomorphies, or transformation series). Phylogenies of either characters or of taxa are historical-narrative explanations (H-N Es), based on both inductively formulated hypotheses and tested against objective, empirical evidence. We further discuss why construction of a “genealogy”, the alleged framework for “evolutionary reconstruction”, based on a taxic, cladistic outgroup comparison and a posteriori weighting of characters is circular. We define how the procedure called null-group comparison leads to the noncircular testing of the taxonomic properties of characters against which the group phylogenies must be tested. This is the only valid rooting procedure for either character or taxon evolution. While the Hennig -principle is obviously a sound deduction from the theory of descent, cladistic reconstruction of evolutionary history itself lacks a valid methodology for testing transformation hypotheses of both characters and species. We discuss why the paleontological method is part of comparative biology with a critical time dimension ana why we believe that an “ontogenetic method” is not valid. In our view, a merger of exclusive (causal and interactive, but best described as levels of organization) and inclusive (classificatory) hierarchies has not been accomplished by a taxic scheme of evolution advocated by some. Transformational change by its very nature is not classifiable in an inclusive hierarchy, and therefore no classification can fully reflect the causal and interactive chains of events constituting phylogeny, without ignoring and contradicting large areas of corroborated evolutionary theory. Attempts to equate progressive evolutionary change with taxic schemes by Haeckel were fundamentally flawed. His ideas found 19th century expression in a taxic perception of the evolutionary process (“phylogenesis”), a merger of typology, hierarchic and taxic notions of progress, all rooted in an ontogenetic view of phylogeny. The modern schemes of genealogical hierarchies, based on punctuation and a notion of “species” individuality, have yet to demonstrate that they hold promise beyond the Haeckel ian view of progressive evolution.     

Description of a new species,Globotruncana pseudoconica and remarks on its relation to Globotruncana conicaWhite and Globotruncana falsostuartiSigal

A new, strongly spiroconvex Globotruncana species,Globotruncana pseudoconica nov. sp., is described from the Maastrichtian of Tunisia. It is distinguished from Globotruncana conicaWhite in morphology and phylogeny. Some Maastrichtian, strongly spiroconvex specimens referred to as Globotruncana conicaWhite, are shown to be identical to Globotruncana pseudoconica nov. sp. The new species reveals close affinity with Globotruncana falsostuartiSigal from which it has evolved during the middle Lower Maastrichtian.     

Myelin Gangliosides in Vertebrates

Abstract: A phylogenetic survey of brain myelin ganglioside patterns and concentrations has been carried out on 16 vertebrate species. Gangliosides were isolated from purified myelin and found to vary in concentration from 25 μg of sialic acid per 100 mg of myeh for goldfish to a value of 395 for turkey. The latter species had approximately equivalent amounts of G_M1 and G_M4 as the two major gangliosides. The 11 mammals studied all had G_M1 as the major ganglioside, with variable amounts of G_M4; rhesus monkey and human had 20-25% G_M4, whereas the others had less than 10%. Amphibia and fish myelin contained the least total ganglioside, with patterns that showed relatively little G_M1 and no detectable G_M4. Alligator myelin was unique in having a total concentration as high as the avian species, but a pattern with predominantly diand trisialo gangliosides.     

Intrinsic Protein Phosphorylation in Synaptosomal Plasma Membrane Fragments: A Comparison of Cerebral Cortex Tissue from Several Species, Including Human Biopsy Specimens

Intrinsic protein phosphorylation was studied in synaptosomal membrane fragments made from cerebral cortex tissue taken from the following species: human (biopsy specimens), ox, rat, rabbit, guinea pig and mouse. Membrane fragments from all species exhibited a qualitatively similar range of protein acceptors phosphorylated by cyclic AMP-dependent protein kinase activity; contrary to a previous report, no evidence for cyclic GMP-dependent protein kinase activity was found in the human material. With the exception of membrane fragments prepared from ox brain, all the preparations exhibited the same range of Ca2+-dependent protein kinase activity. Ox brain obtained from a slaughterhouse yielded membranes containing no Ca2+-dependent protein kinase activity, but this may have been due to unavoidable postmortem losses.