The response of phytoplankton community to anthropogenic pressure gradient in the coastal waters of the eastern Adriatic Sea

In order to test the response of phytoplankton to anthropogenic pressure, data of chlorophyll a concentration, phytoplankton abundance, and composition are analyzed in relation to anthropogenic pressure gradient and environmental variables such as temperature, salinity and nutrients. Investigated sites encompassed wide tropic range according to a preliminary determination of anthropogenic pressure, quantified through the LUSI index. Statistical analyses indicated nitrates and silicates as proxies of freshwater influence, and phytoplankton single metrics such as concentrations of chlorophyll a and abundances as indicators of anthropogenic pressure. Boundary values for different water quality classes for coastal waters under indirect freshwater influence (Type II) are obtained according to gradient between concentration of chlorophyll a and pressure index (LUSI), which empirically fit to exponential equation. The response of phytoplankton diversity was not linear, as the highest diversity was observed in the area with intermediate disturbance level. CCA analysis identified Skeletonema marinoii, Scrippsiella trochoidea, Guinardia flaccida, Leptocylindrus spp., Prorocentrum spp., Proboscia alata, Eutreptiella spp., and Pseudonitzschia spp. as local eutrophication indicators, whose abundances increased with nutrients loads.     

The influence of ants on patterns of colonization and establishment within a set of coexisting lycaenid butterflies in a south-east Asian tropical rain forest

In Peninsular Malaysia ten species of lycaenid butterflies use leaf flushes or inflorescences of the legume tree Saraca thaipingensis as larval hostplant. Resource partitioning among these species is regulated by a complex mixture of patterns of interaction with ants. Females of obligately myrmecophilous species lay their eggs exclusively on trees colonized by their specific host ants. On trees colonized by weaver ants, only specialist mutualists adapted to these territorial ants are able to survive, while larvae of other species are killed. The formicine ant Cladomyrma petalae, which inhabits hollow twigs of the myrmecophytic hostplant, likewise precludes oviposition by female butterflies. Lycaenid larvae confronted with this ant species never survive, but one concealed feeding species (Jamides caeruleus) escapes removal due to the cryptic life-habits of the larvae. Two facultative myrmecophiles associate in a mutualistic way with a wide and largely overlapping range of ant genera which forage at the extrafloral nectaries of leaf flushes. One species (Cheritra freja) is not myrmecophilous, but is tolerated by all but the most territorial ants. Ant-dependent hostplant selection and egg-clustering characterize the obligate mutualists, whereas facultative myrmecophiles and the non-myrmecophile distribute their eggs singly over appropriate hostplants. Signals mediating caterpillar-ant communication are highly specialized in one obligate myrmecophile (Drupadia theda), but rather unspecific in four other species tested. Altogether our observations indicate that colonization and establishment of lycaenid butterflies on S. thaipingensis trees are governed by specializations as well as opportunistic use of resources (ants and hostplant parts). Therefore, the diversity of this species assemblage is maintained by deterministic as well as stochastic factors.     

Species-area curves and estimates of total species richness in an old-field chronosequence

Average species-area curves were generated for vascular plants in 20 old-fields that were sampled in 1983, 1989, and 1994. These curves were fit with a saturating function to estimate total species richness for each old-field. Additional estimates of total species richness were generated by fitting the same saturating function to subsets of the species area curves and with a first-order jackknife procedure. Estimates of total species richness were strongly correlated with observed species richness. There was limited evidence suggesting that greater sampling was necessary to identify the same proportion of species in older, more species-rich old-fields.     

Soil properties and seedling establishment in soils from monodominant and high-diversity stands of the tropical deciduous forests of México

Abstract. The hypothesis that soils from mature monodominant forests are unfavourable for establishment of tree species other than the dominant was tested for a lowland tropical deciduous forest with stands dominated by Celaenodendron mexicanum Standl. (CS). This species of Euphorbiaceae occurs almost exclusively in monodominant stands in which recruitment of other species appears to be poor. Soil properties were examined and experiments were conducted on germination and establishment of Celaenodendron mexicanum and three other species common in adjacent high-diversity mixed stands (MS): Recchia mexicana Moc. & Sessé, Caesalpinia eriostachys Benth., and Cordia alliodora (Ruiz & Pav.) Oken. Soil moisture regimes are affected by topographic position in the study area, but Celaenodendron mexicanum was found occupying hillsides as well as flatlands, and slope gradients of its stands were typical of the region. The microsites occupied in relation to soil moisture and light availability also appear to be undistinctive. There were no significant differences between stand types in any soil property (pH, O.C., total N, total P, avail. P, K, Ca, Mg, Na, Mn, Fe, Cu, Zn concentrations). A stand of intermediate dominance of Celaenodendron (ICS) did not differ from its adjacent mixed stand (MS) in soil texture or most of the nutrients tested; however, seasonally restricted differences in the contents of Fe and Mn (ICSCaesalpinia eriostachys established in both stand types. The results suggest that the distinction between monodominance and high diversity is not maintained by some simple physiological restriction on the establishment of new seedlings.     

Temporal species richness‐biomass relationships along successional gradients

Abstract. Diversity‐biomass relationships are frequently reported to be hump‐shaped over space at a given time. However, it is not yet clear how diversity and biomass change simultaneously and how they are related to each other over time (e.g. in succession) at one locality. This study develops a temporal model based on the projected changes of various community variables in a generalized terrestrial environment after fire and uses post‐fire succession data on Santa Monica Mountains of southern California and other published succession data to examine the temporal diversity‐biomass relationships. The results indicate that in the early stages of succession, both diversity and biomass increase and a positive relationship appears, while in the late stages of succession, biomass continued to increase but diversity usually declines; thus a negative relationship may be observed. When the scales of measurement become sufficiently large so that the measured diversity and biomass cross various stages of succession, a ‘hump‐shaped’ relationship can emerge. The diversity‐biomass relationship appears to be concordant in space and time when appropriate scales are used. Formerly proposed explanations for spatial patterns may well apply to the temporal patterns (particularly colonization, facilitation and competitive exclusion).     

Geographical patterns of persistence in duck guilds

Geographical gradients of persistence in community structure have been suggested to be causally related to underlying gradients of species diversity, environmental variability and/or productivity. In order to test whether the persistence of breeding duck communities was dependent on any one of these three factors, thirty-three years of census data from the Canadian prairie and boreal forest regions was examined along geographical gradients of wetland habitat variability and productivity. For breeding ducks, locally derived patterns of persistence were generally independent of local habitat conditions. Persistence appeared to be related more to patterns of emigration and immigration in response to climatic conditions (i.e., drought) in the southern prairies than to local species richness, wetland habitat variability or productivity. It is suggested, therefore, that analyses of community persistence derived at small spatial scales may be of limited value if the structure of communities is not regulated by local conditions.     

Diversity of cultivable rhizobacteria across tomato growing regions of Karnataka

Seven hundred and fifty-two rhizobacteria were isolated from 186 rhizosphere soil samples collected across tomato growing regions of Karnataka. Among them, 26% strains were Gram positive and other 74% were Gram negative and dominant being Bacillus and Pseudomonas. Sampling of different locations showed variation in species richness and diversity indices. Similarity matrix computed with Jaccard’s coefficient and principle coordinate analysis to correlate bacterial diversity revealed that rhizobacterial genera of Mysore, Mandya and Kolar soil samples were very closely related and rarefaction curve analysis indicated that these soil samples also harbored higher number of rhizobacteria which included all the genera studied. PGPR trait analysis revealed that most of the rhizobacteria were endowed with more than one beneficial trait which may act individually or simultaneously, and indole acetic acid production and phosphate solubilization are the two predominant traits exhibited by these rhizobacteria. Rhizobacterial isolates also showed a varied level of plant growth promotion traits and offered protection against fungal origin foliar and root pathogens. Among the nine regions studied, Mysore, Mandya and Kolar regions recorded higher percentage of promising PGPRs in comparison with other regions studied of Karnataka.     

On the forces that govern clonality versus sexuality in plant communities

Although sexuality is considered evolutionarily progressive, clonality is very common in plants and the prevailing means of reproduction in several community types. I discuss what could be the forces that have influenced the selection among sexual versus non-sexual reproduction at community level. I propose that, among others, the probability of self-competition must have been one of the key factors. The probability of meeting one’s own genes for wasteful competition is higher in communities where clonality prevails (and relatively high mean intra-species relatedness is expected), and higher in communities with low species diversity. On the other hand, lower diversity indicates a higher average fitness of species since the (finite) total pool of resources is distributed among fewer population with high density. I show, using four community types with contrasting diversity and clonality that community fitness (average fitness in the assemblage of species) can be expressed as the product of two variables––anti-diversity and degree of sexuality.     

Maintaining diversity in an artificially propagated population

Populations may suffer unexpected loss or distortion of biodiversity as a consequence of strategies employed in artificial propagation programs. The Trinity River Fish Hatchery may have inadvertently experienced this while attempting to preserve diversity in a return time within a Chinook salmon population. We develop a model for this system and prove that the long-term distribution of return types converges and that it is strongly tied to the management strategy. Given estimates of heritabilities for return type and differential survival rates, an estimate of this long-term distribution can be computed easily.     

Rabbit grazing and species diversity in a dune area

Summary The relation between density of rabbit populations and plant species diversity is discussed. In the dunes of the Dutch Frisian Island of Schiermonnikoog, the rabbit grazing pressure has been quantified on the basis of traces of recent grazing activity. Moderate grazing turned out to bring about maximal species richness. Current changes in grazing pressure (either decrease or increase) can result in plant species diversity that is lower than in other places with equal but stabilized grazing pressure.Nomenclature follows Heukels-van Ooststroom, Flora van Nederland, 18e druk, 1975.The work has been done by Mrs Ada Zeevalking-van Y peren and Mr Hein Zeevalking as part of their study for a doctoral degree.