Information use by an Invading Species: Do Invaders Respond More to Alarm Odors than Native Species?

Two species of crayfish were tested in the laboratory to evaluate the hypothesis that successful invaders use a broader range of chemical information than do displaced native species. The invasive species Orconectes rusticus reduced responses to food odors just as strongly when heterospecific (O. propinquus, O. virilis) alarm odors were introduced with food odors as they did when conspecific alarm odors were introduced at the same time as food odors. Individuals of the displaced native species, O. propinquus, did not reduce feeding responses as strongly when O. virilis alarm odor was introduced as with conspecific alarm odor or O. rusticus alarm odor. These results are consistent with the hypothesis that successful invaders use a wider range of information about their environment than do displaced native species.     

The coincidence of climatic and species rarity: high risk to small-range species from climate change

Why do areas with high numbers of small-range species occur where they do? We found that, for butterfly and plant species in Europe, and for bird species in the Western Hemisphere, such areas coincide with regions that have rare climates, and are higher and colder areas than surrounding regions. Species with small range sizes also tend to occur in climatically diverse regions, where species are likely to have been buffered from extinction in the past. We suggest that the centres of high small-range species richness we examined predominantly represent interglacial relict areas where cold-adapted species have been able to survive unusually warm periods in the last ca 10 000 years. We show that the rare climates that occur in current centres of species rarity will shrink disproportionately under future climate change, potentially leading to high vulnerability for many of the species they contain.     

Influence of continental history on the ecological specialization and macroevolutionary processes in the mammalian assemblage of South America: Differences between small and large mammals

Background  

This paper tests Vrba's resource-use hypothesis, which predicts that generalist species have lower specialization and extinction rates than specialists, using the 879 species of South American mammals. We tested several predictions about this hypothesis using the biomic specialization index (BSI) for each species, which is based on its geographical range within different climate-zones. The four predictions tested are: (1) there is a high frequency of species restricted to a single biome, which henceforth are referred to as stenobiomic species, (2) certain clades are more stenobiomic than others, (3) there is a higher proportion of biomic specialists in biomes that underwent through major expansion-contraction alternation due to the glacial-interglacial cycles, (4) certain combinations of inhabited biomes occur more frequently among species than do others.     

Vertebrate-dispersed species in a fire-prone environment

Abstract It is hypothesized that plant species that produce vertebrate-dispersed seeds (fleshy fruits and brightly coloured arillate seeds) would not be common in fire-prone vegetation because seeds are deposited on the soil surface and are unlikely to survive fires. They have not previously been known to have any means of burial that would enable them to await the next fire as a buried soil seed-bank. We studied vertebrate-dispersed species in fire-prone sclerophyll vegetation to look at mechanisms used by vertebrate-dispersed plants for persisting in these environments. Seeds do not survive heating to 150°C, although species from fire-prone environments are more likely to tolerate moderate heating (80°C) without affecting viability than vertebrate-dispersed species from environments where fire is rare. Most vertebrate-dispersed species have the capacity to regenerate vegetatively, although they are not more likely to have this strategy than ant-dispersed species. Finally, ants do take vertebrate-dispersed seeds and fruits (particularly small ones) indicating the potential for the formation of a soil seed-bank. Some species only persist in fire-prone environments by recolonizing from unburnt areas.     

Evolutionary consequences of ecological release in Caribbean Anolis lizards

On the large islands of the Greater Antilles, multi-species communities of Anolis lizards are composed of species specialized to use particular habitats; similar sets of specialized species have evolved independently on each island. We studied species of anoles found on small Caribbean islands. Because these islands contain at most only one other species of anole, we predicted that species on these islands should not be as specialized as Greater Antillean species; rather, they might be expected to exhibit a generalized morphology and a greater breadth of habitat use. Our findings, however, do not confirm these predictions. Lesser Antillean species do not exhibit greater breadth of habitat use than Greater Antillean species, nor do they exhibit a generalized morphology. Most species are ecologically and morphologically similar to specialized trunk-crown anoles of the Greater Antilles, although some species exhibit morphologies unlike those seen in Greater Antillean species. Among descendants of specialized Greater Antillean species occurring on one-or two-species islands, most descendants of trunk-crown species have diverged relatively little, whereas several descendants of trunk-ground anoles have diverged considerably. Consequently, we propose that ancestral species in the Greater Antilles may have been trunk-crown anoles.     

The creation of specific hominid names: Gloria in excelsis deo? or ego? or praxis?

The recent recommendation that it is preferable to recognize too many rather than too few species in the fossil record has led to a growing proliferation of specific names. Single specimens are being referred to different species by different authors, and new species are being proposed based on the juxtaposition of specimens from different sites and time levels representing different anatomical parts. In part this may represent the continuity of the Medieval assertion that a multitude of species is a better demonstration of the goodness of a divinely created world than a multitude of individuals in a single species. This has apparently accompanied the resurgence of the Medieval faith that species relationship are best demonstrated by the application of hierarchical Aristotelean logic. On the other hand, the suspicion remains that the vanity of the namer is frequently involved in the creation of new nomina. In general, anthropologists do not exhibit the “wide experience” and consequent “sound judgment” that Darwin recommended as necessary for those giving specific names. If the same criteria used to assign specific fossil names were applied to modern Homo sapiens, the different regional human populations would have to be recognized as specifically distinct. In opposition to the recommendation that we should recognize ever more specific names, there should be a moratorium called and no new species names should be proposed at all. The continuation of patterns of trivial trait configurations associated with the various inhabited regions of the world clearly indicates genetic continuity through time but, unless it can be shown that there is no reproductive continuity between one region and another, these differences do not warrant taxonomic recognition. Major adaptive changes such as significant increases in relative brain size do warrant formal named recognition.     

Female marsh wrens do not provide evidence of anatomical specializations of song nuclei for perception of male song

In songbirds the forebrain nuclei HVC (high vocal center) and RA (robust nucleus of the archistriatum) are larger in individuals or species that produce larger song repertoires, but the extent to which the size of these nuclei reflects a need for either producing or perceiving large repertoires is unknown. We, therefore, tested the hypothesis that species differences in the size of song nuclei reflect a commitment of “brain space” to the perceptual processing of conspecific song. The two species of marsh wren (Cistothorus palustris western and eastern) provide a good test case. Western males produce larger song repertoires, and have larger HVC and RA than do eastern males. Female marsh wrens do not sing, and if they use their song nuclei to assess conspecific male song repertoires, then we predicted that measurable cellular and nuclear parameters of HVC and RA would be greater in western than eastern female wrens. For males we confirmed that the volumes of HVC and RA, and cellular parameters of HVC, are greater in western than in eastern birds. These nuclei were also considerably larger in males than in conspecific females. Western and eastern female wrens, however, did not differ in any measured parameters of HVC or RA. Females of these wren species thus do not provide any direct evidence of anatomical specializations of song nuclei for the perceptual processing of conspecific male song. 1994 John Wiley & Sons, Inc.     

Nonadaptive host‐use specificity in tropical armored scale insects

Most herbivorous insects are diet specialists in spite of the apparent advantages of being a generalist. This conundrum might be explained by fitness trade‐offs on alternative host plants, yet the evidence of such trade‐offs has been elusive. Another hypothesis is that specialization is nonadaptive, evolving through neutral population‐genetic processes and within the bounds of historical constraints. Here, we report on a striking lack of evidence for the adaptiveness of specificity in tropical canopy communities of armored scale insects. We find evidence of pervasive diet specialization, and find that host use is phylogenetically conservative, but also find that more‐specialized species occur on fewer of their potential hosts than do less‐specialized species, and are no more abundant where they do occur. Of course local communities might not reflect regional diversity patterns. But based on our samples, comprising hundreds of species of hosts and armored scale insects at two widely separated sites, more‐specialized species do not appear to outperform more generalist species.     

Generalist caterpillar prey are more palatable than specialists for the generalist predator Iridomyrmex humilis

Summary Experiments are described which test the hypothesis that more host-specific species of caterpillars should be less aceptable to a generalist predator than polyphagous species. Caterpillars of all species were tested in paired choice tests with the Argentine ant, Iridomyrmex humilis. Experiments were replicated ten times, videotaped and later analyzed. Brightly colored specialist species (normally considered to be aposematic) were clearly the least palatable, while more cryptic specialists were also significantly less acceptable than generalists overall. Leaf-tying species were considered separately; all were highly palatable independent of host range. The results indicate that among caterpillars that do not construct leaf shelters, those with a wide post range are more acceptable than those with a narrow host range. This is consistent with the notion that generalist predators provide selection pressure favoring narrow host range in their herbivorous prey.     

Positive interactions in plant communities and the individualistic-continuum concept

The individualistic nature of communities is held as a fundamental ecological tenet by many ecologists. The empirical rationale for the individualistic hypothesis is largely based on gradient analyses in which plant species are almost always found to be arranged independently of one another in “continua” along environmental gradients. However, continua are correlative patterns and do not identify the processes that determine them, and so they do not necessarily preclude the possibility of interdependent interactions within plant communities. For example, the common occurrence of positive interactions suggests that plant species may not always be distributed independently of each other. If the distributions and abundances of species are enhanced by the presence of other species, their organization is not merely a coincidence of similar adaptation to the abiotic environment. Interpretations of gradient analyses also appear to assume that interactions among species should be similar at all points along environmental axes, and that groups of species should be associated at all points on a gradient if interdependence is to be accepted. However, virtually all types of ecological interactions have been shown to vary with changes in the abiotic environment, and a number of field experiments indicate that positive effects become stronger as abiotic stress increases. Furthermore, interactions among plants have been shown to shift from competition to facilitation along environmental continua. Thus, significant interdependence may occur even when species do not fully overlap in distribution. Higher-order, indirect interactions between animals and plants, and among plants, also suggest that interdependence within communities occurs. Eliminating a species involved in an indirect interaction may not necessarily mean that its beneficiary will be eliminated from a community, but the prospect that the distribution and abundance of any species in a plant community may be positively affected by the effects that other species have on their competitors suggests that communities are organized by much more than “the fluctuating and fortuitous immigration of plants and an equally fluctuating and variable environment” as stated by Henry Gleason. The ubiquity of direct and indirect positive interactions within plant communities provides a strong argument that communities are more interdependent than current theories allow. Received: 17 February 1997 / Accepted: 23 May 1997     

Distribution of crustacean diapause: micro- and macroevolutionary pattern and process

Theoretical predictions for the relationships between duration of dormancy, reproductive life span, and dispersal ability developed for plants in temporally varying environments are applied here to crustaceans. Mathematical models suggest that diapause duration should negatively covary with adult life span, and that both diapause and life span should negatively covary with dispersal ability. A survey of 167 crustacean species from 20 orders and three classes confirms that species with prolonged diapause have short adult life spans and those with long adult lives either have diapause lasting less than a year, or do not diapause at all. Prolonged diapause is more common among small or inland water crustaceans than it is among large or marine species, whereas large or marine species have significantly longer adult life spans on average than do those that are small or from inland waters. A greater fraction of species in the Branchiopoda exhibit prolonged diapause than do members of the Maxillopoda which, in turn, are more likely to exhibit prolonged diapause than are the Malacostraca. A greater fraction of malacostracan species have adult life spans exceeding one year than do species in either the Branchiopoda or the Maxillopoda. Cladistic analysis shows that phylogenetic constraint is likely to be at least in part responsible for the expression of diapause among the Crustacea. We conclude that both natural selection and macroevolutionary pattern have influenced the distribution of diapause among modern crustaceans.     

Seed Germination Biology of the Narrowly Endemic Species Lesquerella stonensis (Brassicaceae)

Abstract Lesquerella stonensis (Brassicaceae) is an obligate winter annual endemic to a small portion of Rutherford County in the Central Basin of Tennessee, where it grows in disturbed habitats. This species forms a persistent seed bank, and seeds remain viable in the soil for at least 6 years. Seeds are dormant at maturity in May and are dispersed as soon as they ripen. Some of the seeds produced in the current year, as well as some of those in the persistent seed bank, afterripen during late spring and summer; others do not afterripen and thus remain dormant. Seeds require actual or simulated spring/summer temperatures to come out of dormancy. Germination occurs in September and October. Fully afterripened seeds germinate over a wide range of thermoperiods (15/6–35/20°C) and to a much higher percentage in light (14 h photoperiod) than in darkness. The optimum daily thermoperiod for germination was 30/15°C. Nondormant seeds that do not germinate in autumn are induced back into dormancy (secondary dormancy) by low temperatures (e.g., 5°C) during winter, and those that are dormant do not afterripen; thus seeds cannot germinate in spring. These seed dormancy/ germination characteristics of L. stonensis do not differ from those reported for some geographically widespread, weedy species of winter annuals and thus do not help account for the narrow endemism of this species.     

Formal taxa, species groups, and perception of the genus Diplodactylus (Reptilia: Gekkonidae)

Genera with large numbers of species present particular difficulties; the analysis of relationships, of included taxa may be roblematic. One attempt to aproach this problem involves the reco of clusters of species tIat may be informally assembgd into species groups. The problems tE:g the recognition of such assemblages may induce are exlored. It is not that the species groups, as originail formulated, are problematic as they are initiafy erected to demarcate clusters withm an imperfectly known phylogeny of a supposedly monophyletic group. These species groups, however, tend to become recognized as “taxa” rather than operationaf clusters and as such tend to influence the approach to the inclusive taxon taken by subsequent workers. Rather than testing the concept of the species grous, there is a tendency to retain them and to insert other groups between them that do not exactly fit the original scheme. The establishment of species groups, first used to clarify a complex situation, has teen a source of problems for subseuent workers. The history of this aproach is traced for the gekkonid genus Diplodactylus and the problems that have arisen are outlined.     

FLORAL PARAMETERS,BREEDING SYSTEM AND POLLINATOR TYPE IN TRICHOSTEMA (LABIATAE)

Diversity in flower size and degree of exsertion of anthers and stigma from the corolla in the California species of Trichostema appear to be correlated with breeding system and pollinator type (bee vs. bird). Autogamous (self-pollinating) species unlike xenogamous (cross-pollinating) species lack spatially separate anthers and stigma and nototribic pollination. The outcrossing species have significantly larger flowers, significantly larger nectar volumes and significantly higher pollen-ovule ratios than do selfing species. Because autogamous species are less reliant on flower visitors to facilitate pollination, there may be relaxed selection for large nectar producing flowers. Pollen-ovule ratios are correlated with breeding system and reflect the efficiency of pollen transport. Data on floral parameters suggest xenogamous species expend more energy per floral unit and are less efficient seed producers than closely related autogamous species.     

Ecological response syndromes in the flora of southwestern Western Australia: Fire resprouters versus reseeders

Two fire-response syndromes can be described for species of the vegetation of Mediterranean-climate, southwestern Western Australia. Resprouters survive fires as individuals. Reseeders are killed by fire and must reestablish through germination and establishment of seedlings. Of the Western Australian plant families analyzed for fire-response strategies, 50% of the Proteaceae, 50% of the Restionaceae, 45% of the Orchidaceae, and 25% of the Epacridaceae are resprouter species. Within genera of the Proteaceae, the proportions of resprouters includeAdenanthos (56%),Hakea (52%),Dryandra (35%), andGrevillea (31%). WithinBanksia, 49% are resprouters, and it appears that the reseeding syndrome is the derived character in this genus. The proportion of resprouters within southwestern Western Australian plant communities ranges from 66% to 80%. These percentages are generally higher than in more arid parts of Western Australia and in comparable plant communities from other Mediterranean-type climates of the world. The relatively high proportion of resprouters within plant families and within plant communities probably indicates that the Western Australian vegetation experiences a harsher fire stress regime than do other Mediterranean-type climate areas. Western Australian plant communities have their highest diversity in the early years after fire, when the vegetation contains a higher number of reseeding species and individuals. Seed banks are dominated by the seeds of reseeders. There are no basic differences in mean seed mass, viability, or germinability of seeds between resprouting species and reseeding species, but reseeders tend to have narrower optimum germination temperature regimes. Establishment success is related more to seed mass, seedling size, and leaf ecophysiology and morphology than to fire-response strategy. Reseeder seedlings tend to grow faster than do resprouter seedlings. Basic shrub morphology differs, with reseeders generally being umbrella shaped and resprouters urn shaped. Reseeding species most commonly have a shallow, fibrous root system. Resprouters have a massive, deeply penetrating root system. Shoot:root ratios of first-year seedlings and mature plants are higher for reseeders. Resprouter seedlings store starch in root tissue at a much greater rate than do reseeder seedlings. Although the concentrations of essential nutrients in seedlings are not different between fire-response types, reseeders tend to conserve nutrients to a greater extent through leaf retention. Reseeders tend to produce greater numbers of flowers and greater amounts of floral rewards, but the breeding systems, which lead to the higher seed set in reseeders, can vary between strict outcrossing and considerable selfing. Reseeding species are not likely to be wind pollinated. Species survival in a fire-prone environment can involve a wide range of combinations of attributes. It appears that in Western Australian reseeder species the lack of an ability to resprout is compensated for by a number of other structural and functional features. Knowledge of the fire-response strategies of species of southwestern Western Australia can influence fire-regime management, conservation of rare species, and restoration of vegetation after disturbance. Further knowledge of the fire-response strategies of species of the southwestern Western Australian flora should result in better management of natural and restored plant communities of the region.     

Mating systems among European passerines: a review

A review of the mating systems of 122 relatively well-studied European passerines (out of 172 species) is given. Of all species, 39% are polygynous and 25 of the 47 polygynous species are regular polygynists exceeding the limit of 5% polygyny in a population. Of 46 polygynous species, 63% are monoterritorial (having a maximum of one territory), the rest being polyterritorial (having a maximum of more than one territory). Regular polygyny is more common among polyterritorial passerines. Polygyny is frequently found among species breeding in open habitats (marshes, meadows, pastures and low shrubs). Polyterritorial species tend to have tropical winter quarters more frequently than monoterritorial species do. Colonial breeding is absent from the polyterritorial group. Monogamous male passerines participate more frequently in feeding nestlings than their polygynous counterparts do. Regular polygynists tend to be sexually dimorphic in plumage more often than infrequent polygynous passerines, and polyterritorial passerines similarly tend to be plumage dimorphic more often than monoterritorial species. Sexual size dimorphism was more pronounced in monoterritorial than in polyterritorial passerines.     

The transverse orientation of stomata

The orientation of cell walls co-determines development. The orientation of the slits of the stomata can be used for analyzing the factors involved. A comprehensive and annotated list is given of those plant species most of whose stomata are known to be oriented transversely to the long axis of an organ or a main rib. Included are also species showing only a trend toward transverse orientation. Transverse orientation is known from a few mosses, from Bennettitatae, fromAzolla and some other ferns, and from species of about 45 families of spermatophytes. It could be confirmed that succulent species show the trait more often than do other plants. Two thirds of the species listed belong to the Caryophyllales and Santalales, a few only to Asteraceae, but none to Rubiaceae, Cyperaceae, Poaceae, or Orchidaceae. Hence, the incidence of succulent species or of species with some succulent traits within the two orders and the lack of such species among other taxa may account in part for the distribution. On the other hand, many succulent species do not show transverse orientation whereas in, e.g.,Casuarina and Tamaricaceae transverse orientation goes together with non-succulent xeromorphy;Azolla shows no xeromorphy at all. Various factors, separately or together, may be involved. Proposed mechanisms determining the orientation of cell walls have been compiled from literature and are discussed.     

Quantitative Aspects of Antenna Grooming in Bees (Apoidea: Hymenoptera)

Antenna grooming in more than 100 species of bees (Apoidea), representing 34 genera of the 7 major bee families is recorded and quantitatively analysed. Most species of bees fall into one of two groups with respect to repetitive antenna cleaning: “Uniscrapers” predominantly clean their antennae with one stroke, “biscrapers” mostly with two subsequent strokes. Uniscrapers are more consequent in their behaviour than biscrapers. Most biscrapers occasionally clean their antenna with one or three strokes. Individual variation in the ratio of stroke repetition is considerably larger in bi- than in uniscrapers. In several species males and females differ with respect to their antenna cleaning behaviour, females tend to be more uniscraping. Most species of the families Colletidae, Halictidae, and Andrenidae, as well as the species of the genera Ceratina and Nomada (Anthophoridae) are biscrapers. Almost all species of Melittidae, Megachilidae, Apidae, and Anthophoridae (except Ceratina and Nomada) are uniscrapers. Bees with an antenna cleaner with ancestral (plesiomorphic) morphology are mostly, but not always, biscrapers, those with a derived antenna cleaner are always uniscrapers. Bees with a derived antenna cleaner perform on average less cleaning actions and strokes than those with an ancestral antenna cleaner. Uniscrapers with an ancestral strigilis do on average more cleaning actions per minute than biscrapers, thus they compensate partly for the fewer number of strokes. But nevertheless the uniscrapers do fewer strokes than the biscrapers (both with an ancestral strigilis). Females clean their antennae on average more often than males. It is interpreted that the behaviour of uniscraping and a derived morphology of the antenna cleaner result in greater efficiency than the status which is ancestral for Apoidea (biscraping and a plesiomorphic antenna cleaner).     

BIOLOGY AND BEHAVIOUR OF FRIGATEBIRDS FREGATA SPP. ON ALDABRA ATOLL

Both species nested in mixed colonies in mangrove trees. The tops of trees were usually occupied exclusively by minor and the lower parts by ariel, but most nests of both species were in the intermediate parts of the canopy. The main laying season for both species was July to January. A census showed about 27 000 individuals present at the height of the season (1500 breeding pairs of minor, 5350 of ariel). Seasonal variation in numbers could be accounted for almost entirely by the changes in breeding activity of a resident population. Young of both species were fed at or near the nest-site for at least four months after fledging. A recovery near Bombay of a wing-tagged immature ariel shows that this species, at least, undergoes a post-fledging dispersal; it is suggested that young minor either do not disperse, or do so later than ariel. Food samples collected from chicks showed no overall difference between the species, but a seasonal analysis showed that ariel took more squid than minor in the wet season, and in the dry season the two species took different proportions of the two commonest species of flying-fish. Chicks of ariel received smaller meals than minor chicks in the wet season, but similar-sized meals in the dry season; ariel chicks grew more slowly than minor chicks. It is suggested that the timing of the breeding season is related to the need for adults to build up fat reserves to carry them through the courtship, nest-building and laying periods, when they are tied to the colony and so have little opportunity to feed. The evidence for non-annual breeding in frigatebirds is discussed. It is concluded that while successful breeders must breed at intervals of more than 12 months, they could theoretically nest in two successive seasons and that, since breeding success is low, most individuals probably do so. Existing knowledge of the biology of four of the five recognized species of frigatebirds is summarized, and shows that the family is at least as uniform as the tropicbirds and much more so than other Pelicaniformes.