Influence of predation on species coexistence in Volterra models

The possibility of predator-mediated coexistence of all species in model ecosystems of the Volterra type is discussed, that is, asymptotic behaviors of systems of two competing species are analyzed when one or two predators are added. All species in the communities can coexist in two distinct ways mathematically, that is, the species may coexist at equilibrium or may coexist in persistent oscillations. The stability of all species at equilibrium increases when one or two predators are added. The conditions for oscillatory coexistence in limit cycles or in chaotic behaviors of two-predator systems are more complicated than in those of one-predator systems. It is concluded that predator-mediated coexistence can be promoted by an intimate relationship between the competitive ability of the prey and the diet preference of the predators.     

Riparian Forest Restoration Along Large Rivers: Initial Results from the Sacramento River Project

Restoration of riparian vegetation along large rivers is complicated by the patchiness of the habitat and by conflicts with the societal need to control flooding. The Sacramento River Project, led by The Nature Conservancy in northern California, is testing whether it is possible to restore native forest along a large river without removing flood control. We conducted a post-hoc analysis of monitoring data collected by the project on 1–4-year old plantings of 10 native trees and shrubs at five sites. Two questions of general interest were: Can one identify types of species or sites that are especially suitable for restoration in such riparian habitats? To what degree must sites be treated as mosaics of patches, with different types of patches that are suited to different species? Plant performance as measured by height was better in species of Salicaceae or in species planted as cuttings than in species of other families or in species planted as seedings or seeds. Three within-site factors, land form, soil depth to a buried layer of sand or gravel, and soil texture, affected the growth of several species, indicating that sites do need to be treated as patchy. However, there was little evidence that different species performed better on different types of patches. Instead, areas with deep or fine soils seemed to be favorable for a number of species. Results suggest that it is feasible to re-establish native trees and shrubs along large, regulated rivers, at least at certain sites for an initial period of several years with the aid of weed control and irrigation. Shallowly buried layers or lenses of gravel or sand are a hidden, fine-scale factor that can reduce plant growth on river terraces.     

Abundance of introduced species at home predicts abundance away in herbaceous communities

Many ecosystems worldwide are dominated by introduced plant species, leading to loss of biodiversity and ecosystem function. A common but rarely tested assumption is that these plants are more abundant in introduced vs. native communities, because ecological or evolutionary-based shifts in populations underlie invasion success. Here, data for 26 herbaceous species at 39 sites, within eight countries, revealed that species abundances were similar at native (home) and introduced (away) sites - grass species were generally abundant home and away, while forbs were low in abundance, but more abundant at home. Sites with six or more of these species had similar community abundance hierarchies, suggesting that suites of introduced species are assembling similarly on different continents. Overall, we found that substantial changes to populations are not necessarily a pre-condition for invasion success and that increases in species abundance are unusual. Instead, abundance at home predicts abundance away, a potentially useful additional criterion for biosecurity programmes.     

Sex determination and evolution of unisexuality in the Conchostraca

Field collected or laboratory-reared samples of 60 species of conchostracans (representing all extant genera) indicate that males and females are equally common in most species. Deviations from this pattern occur in four lineages.Cyzicus andLeptestheria each include at least one unisexual species; many species of Limnadiinae are either unisexual or characterized by female-biased sex ratios; and Cyclestheriidae are either unisexual or express males in the later generations of their life cycles. Laboratory studies indicate that species with sex ratios near unity are gonochoric (obligately sexual), whereas females in species with female-biased sex ratios are capable of both outcrossing and selfing modes of reproduction. Phylogenetic analysis of patterns of reproduction suggest that sexual reproduction is the primitive condition. Genetic analysis of sexual species indicate that gender is determined by one or a few genetic factors and that the male-determining allele is recessive. The inheritance of gender in androdioecious species (where females are capable of self-fertilization) is similar to that in sexual species. Androdioecy is likely to be the intermediate stage between obligately sexual reproduction and unisexuality in the Limnadiinae. The phylogenetic distribution of sex ratio variation suggests that unisexuality in Cyzicidae, Leptestheriidae, and Cyclestheriidae has arisen independently of that in the Limnadiinae and that these cases have evolved by different evolutionary pathways.     

Interspecific differences in intraspecific abundance-range size relationships of British breeding birds

A general positive interspecific relationship between local abundance and geographic range size in animals has prompted speculation that a similar relationship might exist intraspecifically, such that a species is widespread at times when it is locally abundant, and more restricted in distribution when it is locally rare. Current evidence suggests that intraspecific relationships often are positive, but that there is considerable variation in the pattern exhibited by species. Here, we use data on British birds to test the hypotheses that species showing a high mean or wide spread of local densities or range sizes will be more likely to show strong intraspecific relationships between abundance and geographic range size. These data show only inconsistent support for an effect of the range of densities or of occupancies on intraspecific abundance-range size relationships. However, the strength of an intraspecific relationship does seem to be related to the mean occupancy of species, and whether or not a species exhibits temporal trends in density, with the strongest relationships found in species with simultaneous trends in both density and occupancy. We suggest that these results are explained by time lags in the loss or gain of species at occupied sites in response to reductions or increases in density.     

Precopulatory mating behavior and sexual dimorphism in the amphipod Crustacea

Accounts in the literature of precopulatory mate-guarding in gammaridean amphipods are that males use one of two strategies for mating: either they mate-guard by carrying or attending their mates until they are ready to molt and be fertilized, or they do not guard, instead searching benthically or swarming pelagically at the time that females are ready to molt. Mate-guarding by carrying has been documented for species of the superfamilies Gammaroidea, Talitroidea, and Hadzioidea. Mate-guarding by attending has been found in the more sedentary Corophioidea and Caprellidea. Non-mate-guarders that search pelagically are species of Ampeliscoidea, Lysianassoidea, Phoxocephaloidea, Oedicerotoidea, and Pontoporeioidea. Non-mate-guarders that mate-search benthically are species of Eusiroidea, Crangonyctoidea, and Haustorioidea. Mate-guarding and non-mate-guarding males develop different secondary sex characters at maturity. Mate-guarding males have enhancements for fighting and signalling. These alterations are more elaborate in males that attend their mates than in males that carry their mates. Non-mate-guarders that search pelagically develop enhancements for swimming and sensing. Non-mate-guarders that remain benthic exhibit little change at maturity. Most mate-guarding males develop their secondary sexual characters over several molts and mate over more than one instar. Pelagic mate-searchers develop their secondary sexual characters at the last molt and mating is confined to the last instar. Females of most mate-guarding species are iteroparous, while fewer than half of non-mate-guarding species are so. It is hypothesized that mate-guarding arose more than once in the evolutionary history of amphipod Crustacea.     

Extracellular ion transport

It is a misconception to think that extracellular electric currents of biologic origin are carried by all of the ions in the extracellular medium. It is established that, for certain reasonable boundary conditions, only those ion species that are transported across the plasma membranes of the biological system, or that chemically derive from or contribute to these species, can contribute to the extracellular electric current at steady state. In the absence of convection, the extracellular current will be carried largely by diffusion of the transported ion species, at steady state. Extracellular electric potential gradients are shown to arise in a secondary manner, as a result of the electroneutrality condition. The effect of non-turbulent convection is included in the derivations and discussion.     

Declines in moth populations stress the need for conserving dark nights

Given the global continuous rise, artificial light at night is often considered a driving force behind moth population declines. Although negative effects on individuals have been shown, there is no evidence for effects on population sizes to date. Therefore, we compared population trends of Dutch macromoth fauna over the period 1985–2015 between moth species that differ in phototaxis and adult circadian rhythm. We found that moth species that show positive phototaxis or are nocturnally active have stronger negative population trends than species that are not attracted to light or are diurnal species. Our results indicate that artificial light at night is an important factor in explaining declines in moth populations in regions with high artificial night sky brightness. Our study supports efforts to reduce the impacts of artificial light at night by promoting lamps that do not attract insects and reduce overall levels of illumination in rural areas to reverse declines of moth populations.     

The theory of the nested species–area relationship: geometric foundations of biodiversity scaling

The relationship between sampled area and the number of species within that area, the species–area relationship (SAR), is a major biodiversity pattern and one of a few law‐like regularities in ecology. While the SAR for isolated units (islands or continents) is assumed to result from the dynamics of species colonization, speciation and extinction, the SAR for contiguous areas in which smaller plots are nested within larger sample areas can be attributed to spatial patterns in the distribution of individuals. The nested SAR is typically triphasic in logarithmic space, so that it increases steeply at smaller scales, decelerates at intermediate scales and increases steeply again at continental scales. I will review current theory for this pattern, showing that all three phases of the SAR can be derived from simple geometric considerations. The increase of species richness with area in logarithmic space is generally determined by overall species rarity, so that the rarer the species are on average, the higher is the local slope z. Rarity is scale‐dependent: species occupy only a minor proportion of area at broad spatial scales, leading to upward accelerating shape of the SAR at continental scales. Similarly, species are represented by only a few individuals at fine spatial scales, leading to high SAR slope also at small areas. Geometric considerations reveal links of the SAR to other macroecological patterns, namely patterns of β‐diversity, the species–abundance distribution, and the relationship between energy availability (or productivity) and species richness. Knowledge of the regularities concerning nested SARs may be used for standardizing unequal areas, upscaling species richness and estimating species loss due to area loss, but all these applications have their limits, which also follow from the geometric considerations.     

Comparative osteology and relationships of the Umbridae (Pisces: Salmoniformes)

The phylogenetic relationships of the five living species of umbrids are examined through a comparative osteological study based on a series of cleared-and-stained specimens of each species. The Umbridae appear to be strictly monophyletic. In addition, for 45 characters, the outgroup Esox shares one character-state with at least one umbrid species, while two or more umbrid species share the other state. Assuming that the states shared with Esox are primitive for the Umbridae, the hypothesis that Dallia is more closely related to Umbra than to Novumbra is supported by compatibility and Wagner-tree analysis of the data. Thirteen derived characters are shared by Dallia and Umbra , 20 more are shared by the three species of Umbra , and four more by U. limi and U. pygmaea. Eight characters are considered likely to have undergone reversal or parallel evolution.     

Unusual diversities of seed beetles (Goleoptera: Bruchidae) on Parkia (Leguminosae: Mimosoideae) in Brazil

Earlier studies of the interrelationships between bruchid beetles and their host plants have suggested that the typical pattern tends to be that one bruchid species attacks only a few host species, and that most host species are attacked by only one bruchid species, or at most very few. However, the bruchids attacking Parkia in Amazonian Brazil do not conform to this pattern. The bruchid diversity on Parkia was found to be higher than on any other legume genus yet studied. It is not yet possible to assess whether Parkia is particularly unusual in this regard, or whether such high levels of diversity are typical in Amazonian forests. The number of bruchid taxa attacking any one Parkia species is related to the number of co-occurring closely-related Parkia species. In either taxonomically or geographically isolated host species the bruchid diversity is much reduced.     

The statistical mechanics of community assembly and species distribution

? Theoretically, communities at or near their equilibrium species number resist entry of new species. Such 'biotic resistance' recently has been questioned because of successful entry of alien species into diverse natural communities. ? Data on 10,409 naturalizations of 5350 plant species over 16 sites dispersed globally show exponential distributions both for species over sites and for sites over number of species shared. These exponentials signal a statistical mechanics of species distribution, assuming two conditions. First, species and sites are equivalent, either identical ('neutral') or so complex that the chance a species is in the right place at the right time is vanishingly small ('idiosyncratic'); the range of species and sites in our data disallows a neutral explanation. Secondly, the total number of naturalizations is fixed in any era by a 'regulator'. ? Previous correlation of species naturalization rates with net primary productivity over time suggests that the regulator is related to productivity. ? We conclude that biotic resistance is a moving ceiling, with resistance controlled by productivity. The general observation that the majority of species occur naturally at only a few sites, and only a few species occur at many sites, now has a quantitative (exponential) character, offering the study of species' distributions a previously unavailable rigor.     

Lack of species-specificity in mammalian sperm chemotaxis

Attraction of spermatozoa by way of chemotaxis to substances secreted from the egg or its surrounding cells has been demonstrated in marine species, amphibians, and mammals. This process is species- or family-specific in marine invertebrates: a chemoattractant for one marine species is usually not recognized by another species or by a member of another family. It is not known whether this selectivity is also the rule in other phyla. Furthermore, it is not at all obvious that such selectivity would be advantageous to species with internal fertilization. Here, using a directionality-based assay for chemotaxis, we studied in vitro the chemotactic response of human and rabbit spermatozoa to human, rabbit, and bovine egg-related factors. We found that spermatozoa from each of the two sources responded similarly well to egg-related factors obtained from any of the three species examined. These results indicate lack of chemotaxis-related, species specificity between these species, suggesting that their sperm chemoattractants are common or very similar. The findings further suggest that mammals do not rely on species specificity of sperm chemotaxis for avoidance of interspecies fertilization.     

Aboriginal man as an exterminator of Wallaby and Kangaroo populations on Islands Round Australia

Summary The occurrence of kangaroos, wallabies and related species (Family Macropodidae) on islands of area 90 ha or more round Australia is non-random. Few islands adjacent to the northwestern, northern and eastern coasts have macropods present in contrast to a large number of islands near the mid-and southwestern coasts and most of the southern coastline. The latter group of islands was not visited by aborigines because they lacked watercraft, and most of the islands were apparently too small to support human populations. It is argued that Aboriginal man, through direct predation, his introduction of the Dingo, and his frequent use of fire, was chiefly responsible for the difference in representation of macropods on the two groups of islands.The median area of islands with at least one macropod species present and which are used by Aborigines is about six times larger than that of islands with at least one macropod species present and not visited or occupied by Aborigines. Several possible alternative hypotheses to account for the distribution pattern described above are discussed. For two of these hypotheses inadequate data are at hand to assess their significance.It is suggested that the median area of islands visited or occupied by Aborigines provides a guide to reserve sizes necessary for the conservation of macropods on mainland Australia. Areas of at least 5,000 ha are probably needed for the local long-term persistence of at least one species of macropod, and areas of 9,000 ha for the long-term survival in reserves of at least two macropod species.     

Estimating similarity of communities: a parametric approach to spatio‐temporal analysis of species diversity

Several stochastic models with environmental noise generate spatio‐temporal Gaussian fields of log densities for the species in a community. Combinations of such models for many species often lead to lognormal species abundance distributions. In spatio‐temporal analysis it is often realistic to assume that the same species are expected to occur at different times and/or locations because extinctions are rare events. Spatial and temporal β‐diversity can then be analyzed by studying pairs of communities at different times or locations defined by a bivariate lognormal species abundance model in which a single correlation occurs. This correlation, which is a measure of similarity between two communities, can be estimated from samples even if the sampling intensities vary and are unknown, using the bivariate Poisson lognormal distribution. The estimators are approximately unbiased, although each specific correlation may be rather uncertain when the sampling effort is low with only a small fraction of the species represented in the samples. An important characteristic of this community correlation is that it relates to the classical Jaccard‐ or the Sørensen‐indices of similarity based on the number of species present or absent in two communities. However, these indices calculated from samples of species in a community do not necessarily reflect similarity of the communities because the observed number of species depends strongly on the sampling intensities. Thus, we propose that our community correlation should be considered as an alternative to these indices when comparing similarity of communities. We illustrate the application of the correlation method by computing the similarity between temperate bird communities.     

The role of exotic species in homogenizing the North American flora

Exotic species have begun to homogenize the global biota, yet few data are available to assess the extent of this process or factors that constrain its advance at global or continental scales. We evaluate homogenization of vascular plants across America north of Mexico by comparing similarity in the complete native and exotic floras between states and provinces of the USA and Canada. Compared with native species, exotic plants are distributed haphazardly among areas but spread more widely, producing differentiation of floras among neighbouring areas but homogenization at greater distance. The number of exotic species is more closely associated with the size of the human population than with ecological conditions, as in the case of native species, and their distributions are less influenced by climate than those of native species.     

Environmental factors influencing bird species diversity in Kenya

Sustainable resource management requires understanding the factors that increase or decrease species richness. Regional species richness patterns may be predicted by analysing patterns of variation in the environment. A number of studies have shown that bird species richness at a regional scale is influenced by climatic variables. We examined environmental correlates of bird species richness at a quarter degree square scale (55 × 55 km). Mean annual potential evapotranspiration accounts for 46% of the observed variation in species richness, while mean annual temperature and range annual potential evapotranspiration are significantly correlated with species richness and together account for a further 5% of the observed variation. The results are consistent with the hypothesis that environmentally available energy limits regional species richness.     

The cladistic solution to the species problem

The correct explanation of why species, in evolutionary theory, are individuals and not classes is the cladistic species concept. The cladistic species concept defines species as the group of organisms between two speciation events, or between one speciation event and one extinction event, or (for living species) that are descended from a speciation event. It is a theoretical concept, and therefore has the virtue of distinguishing clearly the theoretical nature of species from the practical criteria by which species may be recognized at any one time. Ecological or biological (reproductive) criteria may help in the practical recognition of species. Ecological and biological species concepts are also needed to explain why cladistic species exist as distinct lineages, and to explain what exactly takes place during a speciation event. The ecological and biological species concepts work only as sub-theories of the cladistic species concept and if taken by themselves independently of cladism they are liable to blunder. The biological species concept neither provides a better explanation of species indivudualism than the ecological species concept, nor, taken by itself, can the biological species concept even be reconciled with species individualism. Taking the individuality of species seriously requires subordinating the biological, to the cladistic, species concept.     

Biodiversity of terrestrial protozoa appears homogeneous across local and global spatial scales

Free-living microbes are by far the most abundant group of organisms in the biosphere, yet estimates of global species richness remain nebulous, and there is no consensus regarding the likely geographical distribution of species. Both uncertainties are addressed by the suggestion that the vast abundance of microbes may drive their ubiquitous random dispersal; for this would also make it likely that global species richness is relatively low. Here we test the idea of ubiquitous dispersal of testate amoebae and ciliates living in soil. We analysed their abundance and species richness in 150 soil samples collected from the one-hectare grassland site at Sourhope in Scotland, and in comparable published data from 1500 soil samples collected worldwide. Following taxonomic revision and removal of synonyms, there remained a total of 186 taxa (91 testate and 95 ciliate) recorded from both Sourhope and other places in the world. A fundamental pattern of random spatial distribution of species was revealed in species that are relatively rare. This probably arises from random dispersal, for when localised population growth occurs, the distributions become aggregated, as in virtually all metazoan species. We find no evidence for geographically-restricted protozoan morphospecies at spatial scales of 4 m², 10,000 m², or worldwide. Species that are locally rare or abundant are similarly rare or abundant on a global scale. Approximately one third of the global diversity of soil protozoa was found at the one-hectare grassland site in Scotland, but this is a minimum figure, for recorded species richness is proportional to sampling effort, as shown here.     

Predicted disease susceptibility in a Panamanian amphibian assemblage based on skin peptide defenses

Chytridiomycosis is an emerging infectious disease of amphibians caused by a chytrid fungus, Batrachochytrium dendrobatidis. This panzootic does not equally affect all amphibian species within an assemblage; some populations decline, others persist. Little is known about the factors that affect disease resistance. Differences in behavior, life history, biogeography, or immune function may impact survival. We found that an innate immune defense, antimicrobial skin peptides, varied significantly among species within a rainforest stream amphibian assemblage that has not been exposed to B. dendrobatidis. If exposed, all amphibian species at this central Panamanian site are at risk of population declines. In vitro pathogen growth inhibition by peptides from Panamanian species compared with species with known resistance (Rana pipiens and Xenopus laevis) or susceptibility (Bufo boreas) suggests that of the nine species examined, two species (Centrolene prosoblepon and Phyllomedusa lemur) may demonstrate strong resistance, and the other species will have a higher risk of disease-associated population declines. We found little variation among geographically distinct B. dendrobatidis isolates in sensitivity to an amphibian skin peptide mixture. This supports the hypothesis that B. dendrobatidis is a generalist pathogen and that species possessing an innate immunologic defense at the time of disease emergence are more likely to survive.