Growth and decline of a penguin colony and the influence on nesting density and reproductive success

Colonial breeding is characteristic of seabirds but nesting at high density has both advantages and disadvantages and may reduce survival and fecundity. African penguins (Spheniscus demersus) initiated breeding at Robben Island, South Africa in 1983. The breeding population on the island increased in the late 1990s and early 2000s before decreasing rapidly until 2010. Before the number breeding peaked, local nest density in the areas where the colony was initiated plateaued, suggesting that preferred nests sites were mostly occupied, and the area used by breeding birds expanded. However, it did not contract again as the population decreased, so that nesting density varied substantially. Breeding success was related positively to the prey available to the breeding birds and negatively to local nest density, particularly during the chick-rearing period, suggesting a density-dependence operating through social interactions in the colony, possibly exacerbated by poor prey availability when the breeding population was large. Although nest density at Robben Island was not high, nesting burrows, which probably reduce the incidence of aggressive encounters in the colony, are scarce and our results suggest that habitat alteration has modified the strength of density-dependent relationships for African penguins. Gaining a better understanding of how density dependence affects fecundity and population growth rates in colonial breeders is important for informing conservation management of the African penguin and other threatened taxa.     

Studies on the Oyster Community in Delaware: The Effects of the Estuarine Environment on the Associated Fauna

The purpose of this study was to determine the composition of the associated fauna of Delaware's oyster beds. Moreover the relative position of Delaware's oyster producing tributaries lends itself to testing the classic hypothesis concerning the effect of salinity on faunal distribution. Interaction of substrate was also studied. The local oyster beds are termed the bay beds which include planted and natural populations, and the river beds. From 1967 to 1971 approximately 800 samples have been collected and the majority of these were from the bay beds. In 1968 and 1969, 132 samples were systematically collected from the river beds and 19 from the bay beds. These were returned to the laboratory for special care in identification. Samples from fouling panels and oyster rafts provided additional species. 152 species were identified but only 133 species were statistically analysed because they were from the systematic collections. Nonparametric statistics were used. In order to facilitate analysis the top 23 species were selected for special treatment. In order of decreasing frequency of occurrence the species were: Sabellaria vulgaris, Conopeum tenuissimum, Panopeus herbsti, Nereis succinea, Palaemonetes vulgaris, Crassostrea virginica, Nassarius obsoletus, Polydora websteri, Membranipora tenuis, Garveia fransiscana, Bulanus improvisus, Diadumene leucolena, Aiptasiomorpha luciae, Melita nitida, Obelia longicyatha, Alcyonidium polyoum, Sertularia argentea, Crangon septemspinosa, Hydroides dianthus, Eurypanopeus depressus, Modiolus demissus, Parapleustes sp., and Hartlaubella gelatinosa. The diversity of species decreases up the estuary with decreasing salinity. Substrate can alter this pattern in particular cases. Within a given salinity range the presence of any firm substrate or mud influenced the nature of the community from epifaunal to infaunal. Four faunal units were recognized: the planted and natural beds, the four southern rivers, the Leipsic River, the Woodland Beach area. The Leipsic River area marks a critical transition zone with a rapid reduction in species. North of Woodland Beach brackish water conditions begin to prevail. The fauna was more diverse in late spring than in the fall but seasonality was not as marked as expected. The faunal composition of Delaware's oyster beds agrees with the cosmopolitan view of estuaries. The stability — time hypothesis proposed by SANDERS provides a theoretical basis to explain faunal distributions in Delaware's oyster community. The hardy nature and geologic history of this oyster community makes it a likely candidate as a sensitive indicator of environmental degradation in the estuary.     

The Distribution of Isopoda in the Delaware Bay Region

The distributions of 24 marine and estuarine isopods have been reviewed. Lironeca ovalis, Aegathoa medialis, Olencira praegustator, and Probopyrus pandalicola were the only parasitic species found. Of the 20 free-living isopods, Asellus communis and Chiridotea almyra were the only fresh to brackish water species, and Chiridotea arenicola, C. stenops, Cirolana impressa, C. polita and Edotea montosa were the true marine species. The salinity range of Cyathura burbancki was extended and the range of Chiridotea stenops was extended northward while the ranges of Chiridotea nigrescens and C. arenicola were extended southward. The contribution of isopod distributions to the concept of a shallow water Transatlantic zoogeographic province is discussed.     

Potential causes of arrested succession in Kibale National Park, Uganda: growth and mortality of seedlings

Recent studies suggest that regeneration following large-scale disturbance in Kibale National Park, Uganda, is slow or possibly arrested. Here, data is provided on the growth and mortality of seedlings in the forest understory, treefall gaps, and in large gaps that suggest that this pattern of arrested succession can be attributed partially to the fact that this East African community lacks aggressive colonizing tree species. Growth and mortality rates were contrasted for seedlings of six tree species planted in the understory, small gaps, and large gaps for 36 months. Data suggest that species are adapted to gaps of particular sizes. For example, Uvariopsis congensis grew faster in the understory than in small gaps, whereas Warburgia ugandensis had the lowest mortality rate and highest growth rate in large gaps. Seedlings (n=170) of 15 species were transplanted to assess the response of the tree community to large gap conditions. The limited survival of seedlings in large gaps relative to the understory suggests that only a small proportion of the tree community in this forest regenerates best in gaps larger than those created by the collapse of a single tree. These findings differ from a number of studies conducted in other geographical regions, and suggests that tree communities differ with respect to the proportion of tree species adapted to gaps of particular sizes. This may relate to variation among regions in their history of disturbance and thus frequency of gap formation, size of gaps, and the duration of periods of release. Such variation could imply the existence of a corresponding pattern among tropical forests of differential vulnerability to human disturbance, which tends to create many large gaps.     

Population structure and evolution of the Bacillus cereus group

Representative strains of the Bacillus cereus group of bacteria, including Bacillus anthracis (11 isolates), B. cereus (38 isolates), Bacillus mycoides (1 isolate), Bacillus thuringiensis (53 isolates from 17 serovars), and Bacillus weihenstephanensis (2 isolates) were assigned to 59 sequence types (STs) derived from the nucleotide sequences of seven alleles, glpF, gmk, ilvD, pta, pur, pycA, and tpi. Comparisons of the maximum likelihood (ML) tree of the concatenated sequences with individual gene trees showed more congruence than expected by chance, indicating a generally clonal structure to the population. The STs followed two major lines of descent. Clade 1 comprised B. anthracis strains, numerous B. cereus strains, and rare B. thuringiensis strains, while clade 2 included the majority of the B. thuringiensis strains together with some B. cereus strains. Other species were allocated to a third, heterogeneous clade. The ML trees and split decomposition analysis were used to assign STs to eight lineages within clades 1 and 2. These lineages were defined by bootstrap analysis and by a preponderance of fixed differences over shared polymorphisms among the STs. Lineages were named with reference to existing designations: Anthracis, Cereus I, Cereus II, Cereus III, Kurstaki, Sotto, Thuringiensis, and Tolworthi. Strains from some B. thuringiensis serovars were wholly or largely assigned to a single ST, for example, serovar aizawai isolates were assigned to ST-15, serovar kenyae isolates were assigned to ST-13, and serovar tolworthi isolates were assigned to ST-23, while other serovars, such as serovar canadensis, were genetically heterogeneous. We suggest a revision of the nomenclature in which the lineage and clone are recognized through name and ST designations in accordance with the clonal structure of the population.     

The helicase domain of the TMV replicase proteins induces the N-mediated defence response in tobacco

Tobacco mosaic virus (TMV) induces the hypersensitive response (HR) in tobacco plants containing the N gene. This defence response is characterized by cell death at the site of virus infection and inhibition of viral replication and movement. A previous study indicated that a portion of the TMV replicase containing a putative helicase domain is involved in HR induction. Here, this observation is confirmed and extended by showing that non-viral expression of a 50 kDa TMV helicase fragment (p50) is sufficient to induce the N-mediated HR in tobacco. Like the HR elicited by TMV infection, transgenic expression of p50 induces a temperature-sensitive defence response. We demonstrate that recombinant p50 protein has ATPase activity, as suggested by the presence of conserved sequence motifs found in ATPase/helicase enzymes. A point mutation that alters one of these motifs abolishes ATPase activity in vitro but does not affect HR induction. These results suggest that features of the TMV helicase domain, independent of its enzymatic activity, are recognized by N-containing tobacco to induce TMV resistance.     

Cortical Network Models of Firing Rates in the Resting and Active States Predict BOLD Responses

Measurements of blood oxygenation level dependent (BOLD) signals have produced some surprising observations. One is that their amplitude is proportional to the entire activity in a region of interest and not just the fluctuations in this activity. Another is that during sleep and anesthesia the average BOLD correlations between regions of interest decline as the activity declines. Mechanistic explanations of these phenomena are described here using a cortical network model consisting of modules with excitatory and inhibitory neurons, taken as regions of cortical interest, each receiving excitatory inputs from outside the network, taken as subcortical driving inputs in addition to extrinsic (intermodular) connections, such as provided by associational fibers. The model shows that the standard deviation of the firing rate is proportional to the mean frequency of the firing when the extrinsic connections are decreased, so that the mean BOLD signal is proportional to both as is observed experimentally. The model also shows that if these extrinsic connections are decreased or the frequency of firing reaching the network from the subcortical driving inputs is decreased, or both decline, there is a decrease in the mean firing rate in the modules accompanied by decreases in the mean BOLD correlations between the modules, consistent with the observed changes during NREM sleep and under anesthesia. Finally, the model explains why a transient increase in the BOLD signal in a cortical area, due to a transient subcortical input, gives rises to responses throughout the cortex as observed, with these responses mediated by the extrinsic (intermodular) connections.