Showing papers in "Biological Journal of The Linnean Society in 1986"
TL;DR: The nested subset hypothesis was formulated to describe and explain patterns in the community structure of insular mammal faunas which are in the state of ‘relaxation’ and suggests that selective extinction of species may be chiefly responsible for the nestedness in natural archipelagos.
Abstract: The nested subset hypothesis was formulated to describe and explain patterns in the community structure of insular mammal faunas which are in the state of ‘relaxation’. The hypothesis states that the species comprising a depauperate fauna should constitute a proper subset of those in richer faunas, and that an archipelago of such faunas arranged by species richness should present a nested series. The non-randomness of this pattern is evaluated for montane mammals in the American Southwest using Monte Carlo simulations under two sets of conditions. First, we constructed model archipelagos with the observed distribution of species richnesses, drawing individual species at random (without replacement) from the species pool (RANDOM0). Secondly, we constructed model archipelagos having the observed distribution of species richnesses, but weighted the selection of species by their actual frequencies of occurrence (RANDOM1). The degree of nestedness in the model archipelagos was then used to assess the non-randomness of the observed structure. Actual Southwestern mammal faunas have a far more nested structure than model archipelagos produced by either RANDOM0 or RANDOM1, and there is virtually zero probability that observed structure is represented in the distribution of scores from either simulation run. Similar analyses were conducted on other archipelagos to determine the generality of this relationship and to identify variables putatively responsible for its production. Mammal faunas of large islands off the coast of Maine, U.S.A., studied by Crowell (1986) also comprise nested subsets, as do those inhabiting islands off the coast of Baja California, Mexico, studied by Lawlor (1983). Significantly, when the Baja archipelago is divided into landbridge islands (which are presumed to be relaxing to lower species level) and oceanic islands (where species number is limited by successful overwater dispersal), only the former show significant nestedness under the more stringent conditions of RANDOM1. These results and theoretical considerations suggest that selective extinction of species may be chiefly responsible for the nestedness in natural archipelagos. Our conclusions have obvious implications for the design of natural preserves (e.g. SLOSS): several small fragments of a single biota can be expected to support nested subsets of the species originally present or that would likely be retained in a single large preserve. Even more sobering are arguments raised which suggest that the faunas of preserves established in different habitats within the same biome might be expected to converge in composition via selective extinction.
942 citations
TL;DR: It is suggested that insular mammalian faunas typically are not in equilibrium, brrause geological and climatic changes can occur as rapidly as colonization and speciation, and any model of island biogeography to be widely applicable to insular faunaas must include speciation as a major variable.
Abstract: Four categories of islands in SE Asia may be identified on the basis of their histories of landbridge connections. Those islands on the shallow, continental Sunda Shelf were joined to the Asian mainland by a broad landbridge during the late Pleistocene; other islands were connected to the Sunda Shelf by a middle Pleistocene landbridge; some were parts of larger oceanic islands; and others remained as isolated oceanic islands. The limits of late Pleistocene islands, defined by the 120 ni bathymetric line, are highly concordant with the limits of faunal regions. Faunal variation among non-volant mammals is high between faunal regions and low within the faunal regions; endcmism of faunal regions characteristically exceeds 70%. Small and geologically young oceanic islands are depauperate; larger and older islands are more species-rich. The number of endemic species is correlated with island area; however, continental shelf islands less than 125000 km2 do not have endemic species, whereas isolated oceanic islands as small as 47 km2 often have endemic species. Geologirally old oceanic islands have many endemic species, whereas young oceanic islands have few endemic species. Colonization across sea channels that were 5-25 km wide during the Pleistocene has been low, with a rate of about 1-2/500000 years. Comparison ofspecies-area curves for mainland areas, late Pleistocene islands, and middle Pleistocene islands indicates that extinction occurs rapidly when landbridge islands are first isolated, with the extent of extinction dependent upon island size; extinction then slows to an average rate of 1-2"/0/10000 years. The great majority of the non-volant Philippine mammals arrived from the Sunda Shelf, the geographically closest of the possible source areas. Speciation within the Philippines has contributed substantially to species richness, perhaps exceeding colonization by a factor of two or more as a contributor to species number. Colonization, extinction and speciation rates differ among taxonomic groups, with murid rodents being most successful and carnivores least successful. In order for any model of island biogeography to be widely applicable to insular faunas, the model must include speciation as a major variable. It is suggested that insular mammalian faunas typically are not in equilibrium, brrause geological and climatic changes can occur as rapidly as colonization and speciation.
400 citations
TL;DR: The present analysis confirms the view that such a selection on sufficiently polymorphic traits for speciation is ecologically realistic and shows that populations with bimodal distributions of some genetically determined quantitative characters can have a considerable life-time.
Abstract: This paper is written to compare the results of theoretical investigations of sympatric speciation with the relevant experimental data. We understand sympatric speciation as a formation of species out of a population whose spatial structure is not important genetically. A necessary prerequisite for speciation is an action of disruptive selection on sufficiently polymorphic traits. The present analysis confirms the view that such a selection is ecologically realistic. The genetical part of speciation begins with a development of reproductive isolation between those individuals that are opposed in some characters. It is shown that selection for reproductive isolation may be quite strong. Extinction of intermediate individuals, which completes speciation, proceeds under a wide range of conditions, including those when the newly formed species differ in quantitative characters, though most of the genes arc likely to remain the same in both species. The whole process seems possible if differences in several (up to 10) loci are sufficient to adapt the forming species to different niches and to establish reproductive isolation. It is shown that populations with bimodal distributions of some genetically determined quantitative characters can have a considerable life-time. Such distributions may be formed either as a transition stage of sympatric speciation or represent a stationary state under conditions close to those necessary to complete speciation. They are very important for experimental investigations. Sympatric speciation always follows the same principal course; it does not contradict the idea of a genome coadaptedness. The occurrence of sympatric speciation is different for different taxa depending rather on how frequently populations are subjected to the appropriate kind of selection than on their ability to obey it.
200 citations
TL;DR: It is found that the evolutionary divergence of character plasticities could be independent of the interspecific divergence ofcharacter means, and there was a tendency for the divergence of amounts and patterns of plasticity to be related.
Abstract: Phenotypic plasticity is an important mode of adaptation to temporal and spatial environmental variability, particularly in plants. Although data are available concerning interspecific differences in the sizes and shapes of characters, there is little information concerning differences between taxa for the plastic responses of those characters. We have measured: (1) the mean value of a character, (2) the amount of character plasticity, and (3) the pattern of phenotypic plasticity for species in five genera, and calculated the divergences among species for each of these three measures. We compared the divergences of these measures to address the question of whether there is a relationship between the evolution of the character means of species and the evolution of the plasticities of those characters. We found that the evolutionary divergence of character plasticities could be independent of the interspecific divergence of character means. There was, however, a tendency for the divergence of amounts and patterns of plasticity to be related.
178 citations
TL;DR: The timing and causes of extinctions of West Indian land mammals during three time intervals covering the last 20000 years (late Pleistocene and early Holocene, Amerindian, and post-Columbian) are discussed in detail.
Abstract: The timing and causes of extinctions of West Indian land mammals during three time intervals covering the last 20000 years (late Pleistocene and early Holocene, Amerindian, and post-Columbian) are discussed in detail. Late Pleistocene extinctions are attributed to climatic change and the post-glacial rise in sea level, whereas most late Holocene extinctions are probably human caused, resulting from predation, habitat destruction and introduction of exotic species. Extinctions have dramatically altered the composition of the non-volant mammal fauna, but have had a lesser impact on bats. Of the 76 recognized species of living and extinct non-volant mammals in the West Indies, 67 species (88%) have gone extinct since the late Pleistocene, whereas only eight of the 59 species of bats (14%) have disappeared during this same time interval. A larger percentage of Antillean bat species (24%) have suffered localized extinction on certain islands, particularly obligate cave-dwelling forms. These local extinctions occurred primarily on small islands, and probably resulted from changes in cave microclimates and flooding of low-lying caves by rising sea levels.
The majority of West Indian bats and all of the edentates, primates and rodents are Neotropical in origin. The South American fossil record indicates that most West Indian terrestrial mammals did not evolve until the early Miocene or thereafter. The Caribbean islands had assumed essentially their modern position and configuration by the Miocene, thus leaving overwater dispersal as the primary mechanism by which these endemic South American mammal groups reached the islands. The primitive insectivores, Solenodon and Nesophontes, are derived from Early Tertiary forms in North America that may have reached the islands through vicariance by way of a proto-Antillean archipelago. Many of the bats are either conspecific or congeneric with mainland taxa, suggesting that most species reached the islands by overwater dispersal during the Late Cenozoic, primarily from Central and South America.
Two hypothetical immigration rates are calculated for West Indian land mammals, one assuming the earliest colonization in the late Eocene and the other based on an early Miocene origin. The known Late Quaternary and living Antillean land mammal fauna was derived from approximately 50 separate colonization events (13 for non-volant mammals and 37 for bats) giving immigration rates of one species per 800000 years since the late Eocene, or one species per 400000 years since the early Miocene. Immigration rates for bats are approximately three times greater than those for non-volant mammals throughout the Tertiary and eight times greater in the Pleistocene, presumably reflecting their greater dispersal abilities. These immigration rates should be considered rough values, owing to deficiencies in the fossil record, especially the absence of pre-Pleistocene fossils. Extinction rates calculated for the last 20 000 years demonstrate that an average of one species of mammal went extinct every 267 years during that time period. Since the arrival of man in the West Indies some 4500 years ago, 37 species of non-volant mammals have disappeared giving the rapid extinction rate of one species every 122 years. Island area-species diversity curves are plotted for both the current and late Pleistocene mammal faunas. All Caribbean islands with a reasonably complete fossil record have more species in the late Pleistocene and Holocene than in the living fauna. The living non-volant mammals of the West Indies do not constitute a natural fauna, but are an impoverished subset of species that managed to escape the extinctions that decimated the remainder of the fauna. Historical or theoretical biogeographic analyses of Antillean mammals that fail to incorporate extinct forms will be unlikely to elicit any meaningful patterns.
165 citations
TL;DR: The captive jacamars were able to discriminate between the very similar colour patterns of some Batesian mimics and their models, and could memorize the palatability of a large variety of butterflies.
Abstract: Wild rufous-tailed jacamars (Galbula ruficauda) were shown to prey frequently, but selectively, upon butterflies in a Costa Rican rainforest. Two individually caged birds (a male and a female) were further tested with over 1000 butterflies of 114 morphs. Both wild jacamars and the two captive individuals were able to capture and handle all kinds and sizes of local butterflies. These butterflies (and other winged insects) were recognized by the jacamars as prey only through their movement. The captive birds discriminated between an unacceptable group of butterflies, which generally fly slowly or regularly, are warningly coloured and mimetic, with transparent, or white, orange, red, and/or black coloration, and an acceptable group that generally fly fast or erratically, are cryptic (on one or both sides), and have yellow, orange, green, blue, and/or brown coloration. These different morphological and behavioural characteristics of butterflies presumably helped the jacamars to assess their palatability.
Most individuals of unacceptable butterflies (e.g. Battus and Parides (Papilionidae), some Pieridae, Diaethria and Callicore (Nymphalinae), Heliconiinae, Acraeinae, Ithomiidae, and Danaidae) were sight-rejected by the male jacamar (Jacamar 2), and many of the same were also sight-rejected by the female (Jacamar 1). In cases when the above butterflies were attacked, they were quickly released and usually unharmed. The captive female bird, after long periods without food, consumed many pierid and heliconiine butterflies that were consistently rejected by the male for their distasteful and dangerous qualities. In contrast, palatable butterflies (e.g. Papilio, Charaxinae, most Nymphalinae, Morpho, Brassolinae, and Satyrinae) were usually quickly attacked and consumed. The captive jacamars were able to discriminate between the very similar colour patterns of some Batesian mimics and their models, and could memorize the palatability of a large variety of butterflies. The discriminatory abilities of specialized insectivorous birds such as jacamars are likely to play a major role in the evolution of neotropical butterfly mimicry.
165 citations
TL;DR: The spatial patterns and environmental correlates and predictors of genetic variation of H, spontaneum in the Fertile Crescent indicate that genetic variation in wild barley populations is not only rich but at least partly adaptive and predictable by ecology and allozyme markers.
Abstract: Genetic diversity and structure of populations of the wild progenitor of barley, Hordeum spontaneum, from three countries, Israel, Turkey and Iran, in the Near East Fertile Crescent, are compared and contrasted. The analysis is based on electrophoretically discernible allozymic variation in proteins encoded by 27 shared loci in 2125 individuals representing 52 populations of wild barley. The results indicate that: (a) H. spontaneum in the Near East Fertile Crescent is very variable genetically; (b) genetic differentiation of populations includes some clinal but primarily regional and local patterns often displaying sharp geographic differentiation over short distances; (c) the average relative genetic differentiation (Gst) was 54% within populations, 39% among populations, and 8% between the three countries; (d) allele distribution is characterized by a high proportion of unique alleles (51%), and a high proportion of common alleles that are distributed either locally or sporadically; (e) discriminant analysis by allele frequencies successfully clustered wild barley of each of the three countries (96% correct classification); (f) a substantial portion of the patterns of allozyme variation in the wild gene pool is significantly correlated with the environment and is predictable ecologically, chiefly by a combination of humidity and temperature variables; (g) natural populations of wild barley are, on the average, more variable than two composite crosses and land races of cultivated barley. The spatial patterns and environmental correlates and predictors of genetic variation of H, spontaneum in the Fertile Crescent indicate that genetic variation in wild barley populations is not only rich but at least partly adaptive and predictable by ecology and allozyme markers. Consequently, conservation and utilization programmes should optimize sampling strategies by following the ecological-genetic factors and allozyme markers as effectively predictive guidelines.
139 citations
TL;DR: This work examines 42 electrophoretically detectable loci in natural and transplanted charr populations from 15 localities in S Norway to propose that the morphotypes reflect a complex of at least three sibling species, and the multiple species hypothesis is rejected.
Abstract: The systematica of coexisting morphotypes of Arctic charr, Salvelinus alpinus, has been a matter of dispute ever since the days of Linnaeus. Widespread allelic variation at an esterase locus has led some investigators to propose that the morphotypes reflect a complex of at least three sibling species. We tested this hypothesis by examining 42 electrophoretically detectable loci in natural and transplanted charr populations from 15 localities in S Norway. The absolute values of Nei's genetic distance between morphotypes and populations are small (typically in the order of 0.001), and morphotype changes may occur without accompanying changes in frequencies of esterase alleles. Differentiation among localities explains far more of the total gene diversity than differences between morphotypes in the four cases of naturally occurring sympatric morphotypes examined. The data are consistent with an intraspecific population structuring based on locality, and the multiple species hypothesis is rejected.
135 citations
TL;DR: The results suggest that fitness is positively correlated with heterozygosity and support the niche-width-variation hypothesis in regard to pollutants and have practical implications for the identification of optimum marine species as genetic monitors of pollution.
Abstract: We tested in the laboratory three pairs of species belonging to three genera and families of marine gastropods, Monodonta turbinata, M. turbiformis (Trochidae), Littorina punctata, L. neritoides (Littorinidae), Cerithium scabridum, C. rupestre (Cerithiidae), for resistance to diverse inorganic (heavy metals and NaC1) and organic (detergents and crude oil) pollutants. Each pair consisted of one narrow-niche species with low genetic diversity and one broad-niche species with higher genetic diversity. Evidence is presented that in all three cases the species with a higher level of genetic diversity was more resistant to all pollutants than its counterpart. These results suggest that fitness is positively correlated with heterozygosity and support the niche-width-variation hypothesis in regard to pollutants. The results also have practical implications for the identification of optimum marine species as genetic monitors of pollution.
125 citations
TL;DR: Insular faunas of terrestrial mammals and bats are examined on a worldwide basis to test the adequacy of equilibrium and historical legacy models as explanations for species- area relationships and no support is found for alternative hypotheses to explain low species-area slopes for terrestrial mammals on oceanic islands.
Abstract: Insular faunas of terrestrial mammals and bats are examined on a worldwide basis to test the adequacy of equilibrium and historical legacy models as explanations for species-area relationships. Species numbers of bats on islands conform to predictions from equilibrium theory, whereby recurrent immigrations and extinctions influence species richness. By contrast, species numbers of terrestrial mammals on islands result from a historical legacy of very low immigration rates on oceanic islands (the faunas are colonization-limited) and by the fragmentation of once contiguous continental faunas to form relictual populations, which subsequently undergo extinctions, on landbridge islands (the faunas are extinction-limited). This explanation is supported by several lines of evidence: (1) z values (slopes of species-area curves) are lower for non-volant mammals on oceanic islands than for those on landbridge islands, but are the opposite for bats; (2) z values for non-volant mammals are lower than those for bats on oceanic islands, but are higher than those for bats on landbridge islands; and (3) landbridge island faunas are attenuated mainland faunas, whereas those on oceanic islands are ecologically incomplete. No support is found for alternative hypotheses to explain low species-area slopes for terrestrial mammals on oceanic islands.
124 citations
TL;DR: Size variation of body and skull of five species of Australian mammals, including red kangaroo, is related to climatic factors, and body size is correlated with indices of biomass productivity and ambient temperature.
Abstract: Size variation of body and skull of five species of Australian mammals (echidna, Tachyglossus aculeatus; brush-tail possum, Trichosurus vulpecula; eastern grey kangaroo, Macropus giganteus; western grey kangaroo, M. fuliginosus; red kangaroo, M. rufus), is related to climatic factors. All five species show trends in body size that conform with Bergmann's rule, individuals from colder environments being larger than those from warmer areas. The western and eastern grey kangaroos also conform with Allen's rule, the relative size of their extremities being large in warmer areas. In four of the five species (not the red kangaroo) body size is also correlated with indices of biomass productivity. However, since biomass productivity and ambient temperature are related to some extent, it is difficult to separate the effects of these factors.
TL;DR: The sperm displacement ability of damselflies has been investigated in this paper, showing that males of the coenagrionid damselfly Argia moesta, A. sedula and hchnura ramburii use similar penis morphology to remove and/or reposition sperm of previous males from the storage organs of females prior to inseminating them.
Abstract: Males of the coenagrionid damselflies Argia moesta, A. sedula and hchnura ramburii use similar penis morphology to remove and/or reposition sperm of previous males from the storage organs of females prior to inseminating them. Although the species vary in the degree to which sperm is removed from or packed into the spermatheca, in all three species, sperm is removed from the bursa copulatrix. Since sperm in the bursa probably has priority in fertilizing eggs in at least the first oviposition after mating, sperm precedence can be estimated as the percentage of sperm (by volume) in the bursa belonging to the last male to mate. Estimated sperm precedence for these species is approximately 71% for Argia sedula, 82% for I. ramburii and 93% for A. moesta. These results, combined with similar ones for other damselflies clearly indicate that the ability to displace sperm may be widespread among temperate-zone Zygoptera. Species with each of the four major variations in damselfly penis structure have now been shown to displace sperm using this morphology. The systematic distribution of these major variants suggests several origins of sperm displacement ability within the Zygoptera. Whether or not all damselflies are capable of sperm displacement depends on both the presence of micro-structures used in sperm removal or repositioning and on the presence of sperm of previous males in mating females. It is possible, therefore, to predict that sperm displacement occurs in a damselfly if (1) females mate more than once, (2) mating females store sperm in organs accessible to penis morphology, (3) the distal segment of the male penis has structures similar to those known to be involved in sperm removal or repositioning, and (4) oviposition occurs in tandem or with the male non-contact guarding his mate.
TL;DR: It is suggested that the concept of a fixed critical minimum area for isolated populations may be meaningless unless immigrations are unimportant with respect to the fauna under study, and apparently anomalous or stochastic distribution patterns of insular species may readily be explained by the deterministic model presented here.
Abstract: A general review of the patterns of species richness of insular mammals (Lomolino, 1984a) indicated that richness is determined by interactive as well as additive effects of factors affecting immigration and extinction. The present paper reports that species composition of insular mammals is also influenced by such additive and interactive effects. Therefore, insular incidence should be high for those species whose (or on those islands where) (immigration rates) are high relative to extinction rates. The model presented in this paper predicts that species have high incidence on islands if low immigration rates (poor immigrators and/or distant islands) are compensated by low extinction rates (good survivors and/or large islands), or high extinction rates are compensated for by high immigration rates. Therefore, poor immigrators may be frequent inhabitants of distant islands if their extinction rates are compensatorily low (large islands and/or low resource requirements). Conversely, extinction-prone species (large, specialist carnivores) may be frequent inhabitants of small islands if their immigration rates are compensatorily high (near islands and/or good immigrators). These ‘compensatory effects’ were well evidenced by the mammalian faunas of the islands in the Thousand Islands Region, New York, and Lake Michigan (U.S.A.). ‘Compensatory effects’ are also evidenced by mammals of other archipelagos, as well as by birds inhabiting real and habitat islands. These results are consistent with the fundamental assumption of the equilibrium theory of island biogeography, i.e. insular community structure is the result of recurrent (rather than unique) immigrations and extinctions. Accordingly, I suggest that the concept of a fixed critical minimum area for isolated populations may be meaningless unless immigrations are unimportant with respect to the fauna under study. Finally, apparently anomalous or stochastic distribution patterns of insular species may readily be explained by the deterministic model presented here which incorporates the interactive as well as additive effects of immigration and extinctions on insular community structure.
TL;DR: The general reduction of genetic variance in island populations compared to continental forms of the same species suggests that founder events have played a major role in the formation of most island forms, but there is ample evidence of adaptation in Island populations despite this lower variation.
Abstract: Island populations are of interest for their differentiation as well as their species diversity; some of the earliest biological interest in islands was concerned with the number of ‘endemics’ thereon. There is dispute about the long-term evolutionary importance of island forms, but they are rich sources of data for studying the under-exploited interface of genetics, ecology and physiology. Differentiation of island populations may arise from genetic change after isolation, or from the chance collection of alleles carried by the colonizing group itself. The general reduction of genetic variance in island populations compared to continental forms of the same species suggests that founder events have played a major role in the formation of most island forms. However, there is ample evidence of adaptation in island populations despite this lower variation; this is relevant when using island biology as a base for the deriving of rules for genetic conservation.
TL;DR: It is suggested that mite pockets have evolved in forms prone to trombiculid infestation and are suggested to ameliorate the damage that this causes by concentrating chiggers in places that are equipped to minimize the harm they do.
Abstract: Many scattered lizard groups have small skin invaginations in such places as the neck, axilla, groin and postfemoral region. These frequently contain feeding chiggers (the larvae of trombiculid mites) which, in general, are much commoner on species with pockets than on those without. Mite pockets appear to have evolved many times, being found in at least five families (Iguanidae, Chamaeleonidae, Gekkonidae, Lacertidae, Scincidae) and are most abundant in warm areas that are not extremely dry. They are present in newly hatched animals and embryos of viviparous forms and so cannot be produced in direct response to the mites. Typically, the epidermis of infested pockets is hyperplastic and resilient, rapidly repairing damage caused by feeding mites, and the dermis contains dense concentrations of lymphoid cells. It is suggested that mite pockets have evolved in forms prone to trombiculid infestation and ameliorate the damage that this causes by concentrating chiggers in places that are equipped to minimize the harm they do.
TL;DR: Three of the six species of shrew in Finland, Sorex araneus, S. caecutiens, and S. minutus, are common on the mainland and widespread on islands in lakes; these factors probably contribute to the absence of the small species from many islands tens of hectares in area.
Abstract: Three of the six species of shrew in Finland, Sorex araneus, S. caecutiens, and S. minutus, are common on the mainland and widespread on islands in lakes. The islands range from 0.01 to 500 ha in area, and from 10 to 3000 m in isolation (distance from the mainland). The species-area relationship, the lack of importance of habitat diversity, the increasing frequency of unoccupied small islands with isolation, and direct observations of small populations, all suggest that populations on small islands have a high extinction rate. Demographic stochasticity is the main cause of extinctions in the superior competitor, S. araneus, which occurs consistently on islands greater than 2 ha. The small species, S. caecutiens and S. minutus, are more sensitive to environmental stochasticity than is S. araneus, and are inferior to it in interspecific competition; these factors probably contribute to the absence of the small species from many islands tens of hectares in area. Frequent colonization of islands less than 500 m from the mainland is indicated by large numbers of shrews trapped from tiny islets where breeding is not possible, by increasing epigenetic divergence of island populations with isolation, and by observations of dispersal to and colonization of islands. Dispersal ability decreases with decreasing individual size, which may partly explain the absence of the small shrews from many relatively large islands. The shrew populations persist in a dynamic equilibrium on the islands. Epigenetic morphological variation is a useful tool in ecological studies of island populations.
TL;DR: It is suggested that particular attention be given to area and elevation when designing naturc reserves, and vegetative cover diversity is a poor predictor of mammalian species richness in western North American national parks.
Abstract: The relationship between non-volant mammalian species richness and area in 24 western North American national parks is examined. The exponential and the power function models are concluded to be the ‘best’ models and account for nearly an identical proportion of the total variance ( g 69‘!/”). Two principal hypotheses, the area per se and the habitat diversity hypotheses, have been proposed to explain the species-area relationship. Support exists for both hypotheses based upon partial correlation analysis of non-volant mammalian species richness with area, elevational range, latitude, number of vegetative cover types and index of vegetative cover divrrsity. I conclude that area per se and habitat diversity defined as environmental heterogeneity are the best predictors of non-volant mammalian species richness in western North American national parks. I also conclude that vegetative cover diversity is a poor predictor of mammalian species richness in western North American national parks. Several problems with assessing the area per se and habitat diversity hypotheses are noted. These are: (1) the definition of the term ‘habitat’; (2) the predictions of these two hypotheses may not be mutually exclusive; and (3) area and habitat diversity tend to be intercorrelated. The slope (2) of the power function is equal to 0.12. The hypothesis that variation in the slope of the power function for nature reserves worldwide is a result of the comparativr sizes of the nature reserves cannot be excluded. There has been considerable discussion in recent years about the conservation implications of the species-area relationship. Much of this discussion has been concerned with whether a single large reserve contains more species than scveral small reserves (SLOSS). lhe answer to SLOSS is heavily dependent upon the objectives of a reserve, the autecology of the species, and the ecological independence of the reserves. It is suggested that particular attention be given to area and elevation when designing naturc reserves.
TL;DR: It is concluded that while some insular populations may be relictual, the faunal composition of most of these islands is dependent on recurrent colonization, much of which takes place over ice bridges, and true equilibrium is perturbed by climatic shifts, range expansions, and human disturbance.
Abstract: For the mammalian faunas of 24 landbridge islands in the Gulf of Maine (0.003–279 km2 in size), area accounts for 86% of variance in species richness. The slope, z, of the species-area curve is 0.247. For the seven largest islands (>10km2), the non-equilibrium hypothesis of relaxation following saturation in the post-Pleistocene is suggested by (1) elevated slope of the species-area curve (0.353), (2) correlation of species richness with island age (r=- 0.81) and water depth to mainland (r= -0.70), (3) highly non-random nested subsets of species ranked by island area, and (4) discontinuity with the extremely depauperate faunas of oceanic islands of the eastern North Atlantic. The alternative hypothesis of a dynamic equilibrium determined by recurrent immigration and extinction is supported by (1) documented turnover in 16 species, (2) correlation of species-area residuals with distance (r= - 0.90), (3) distribution dependent upon vagility with reduction or absence of hibernators and other poor dispersers, (4) low levels of endemism, and (5) congruence of community structure with that of mainland fauna for both trophic level and body size.
I conclude that while some insular populations may be relictual, the faunal composition of most of these islands is dependent on recurrent colonization, much of which takes place over ice bridges. However, true equilibrium is perturbed by climatic shifts, range expansions, and human disturbance.
TL;DR: The problems associated with the identification of lepidopterous fossils (Insecta) are discussed and the origins and evolution of scales in the Amphiesmenoptera (Lepidoptera + Trichoptera) is considered.
Abstract: The problems associated with the identification of lepidopterous fossils (Insecta) are discussed. The origins and evolution of scales in the Amphiesmenoptera (Lepidoptera + Trichoptera) is considered. An illustrated review of the 19 Mesozoic insects described as lepidopterous is given and their identity discussed. Ample evidence of diversity of Lepidoptera in the Cretaceous, evidence (two specimens) of their presence in the Jurassic and some evidence of their presence in the Triassic is given.
TL;DR: Confusion results from a failure of many biologists writing on this subject to adequately consider the variation in life-cycles existing between major taxa and from a general failure by botanists and mycologists to distinguish between automixis and autogamous forms of self-fertilization (in which the fusing nuclei derive from different meioses).
Abstract: Biologists have conclusively failed to arrive at a generally acceptable definition of sexual reproduction. Because of this, several reproductive processes are seen as sexual by some authors but as asexual by others. Included among these are automictic methods of reproduction. Automixis describes several reproductive processes whereby a new individual derives from a product or products of a single meiotically dividing cell. Several forms involve an episode of nuclear fusion and it is argued that, because of this, they should be seen as sexual processes irrespective of whether the fusing bodies are differentiated as gametes or are simply meiotic tetrad nuclei. Other forms involve no episode of nuclear fusion and it is argued that, because of this, they should be seen as asexual processes. These latter forms involve the generation of diploid eggs either by restitutional meioses, or by an endomitotic event preceding or following a reductional meiosis, or involve the generation of a diploid embryo by the fusion of cleavage division nuclei in a haploid embryo; in each case the egg develops parthenogenetically.
In addition to the disagreement that exists over the reproductive status of automixis, considerable confusion exists over its taxonomic distribution. It is often described as being restricted to a few species of insects, where it is parthenogenetic, but in factde range of taxa, including both isogamous and anisogamous plants and fungi, where it may be either parthenogenetic or non-parthenogenetic. This confusion results both from a failure of many biologists writing on this subject to adequately consider the variation in life-cycles existing between major taxa and from a general failure by botanists and mycologists to distinguish between automixis and autogamous forms of self-fertilization (in which the fusing nuclei derive from different meioses). It is further compounded by a proliferation of synonyms for automictic processes. Thus in a number of publications automictic processes are variously described as being matromorphic, thelytokous, parthenogamic, autogamic or apomictic rather than as being automictic.
TL;DR: Analysis of insular distributions show unequivocally that probabilities of extinction, colonization and speciation are highly deterministic and vary in predictable ways among different taxa and archipelagos, which have important implications for applying the theory and data ofinsular biogeography to the pressing practical problems of designing natural reserves to preserve native species.
Abstract: More than two decades after its publication, MacArthur and Wilson’s equilibrium model of insular biogeography continues to provide the conceptual foundation for investigating the distribution of species on islands and the composition of insular biotas. During this period, studies of the distributions of mammals among insular habitats have tested, modified, and extended MacArthur and Wilson’s simple formalism to enhance greatly our understanding of the complexities of biogeographic patterns and processes. The papers in this symposium summarize many of the past contributions of mammalian biogeographers and introduce important new data and ideas. The diversity of biological characteristics and associated distributional patterns exhibited by mammals has facilitated this endeavour. Some insular mammalian faunas appear to represent approximate equilibria between opposing rates of contemporary colonization and extinction. Other faunas are currently decreasing in diversity because of extinctions, owing either to natural habitat fragmentation that has occurred since the Pleistocene or to human activities within the last few centuries. Still other faunas have been increasing in diversity (at least until recent human impacts) because limiting rates of origination, both colonization and speciation, have been extremely low. The questions and analyses of island biogeography can also be applied to continents with comparable overall results: the distributions of continental faunas reflect the consequences of similar processes of colonization, speciation and extinction. Analyses of insular distributions show unequivocally that probabilities of extinction, colonization and speciation are highly deterministic and vary in predictable ways among different taxa and archipelagos. These findings have important implications for applying the theory and data of insular biogeography to the pressing practical problems of designing natural reserves to preserve native species.
TL;DR: An example of convergent evolution, Lizard toe fringes are composed of laterally projecting elongated scales and have arisen independently at least 26 times in seven families of lizards, and shows a strong association with substrate type.
Abstract: Lizard toe fringes are composed of laterally projecting elongated scales and have arisen independently at least 26 times in seven families of lizards. Four different fringe types are identified: triangular, projectional, conical and rectangular. To determine if variation in fringe morphology can be attributed to environmental differences, each independent evolution of a fringe type is identified; correlation of substrate types with evolutionary independent fringe morphologies are then studied. Variation in fringe morphology shows a strong association with substrate type: triangular, projectional and conical fringes with windblown sand; and rectangular fringes with water. Some aspects of fringe morphology may result from differences in functional requirements, and others may have no adaptive significance. This example of convergent evolution points out difficulties inherent to comparative studies of adaptation and underscores the value of broad comparative surveys which provide an alternative to ad hoc adaptive explanations of similarity.
TL;DR: Experiments on pollen flow and seed production were performed in populations of P. vulgaris to examine the roles of selection for reduced self-pollination in a partially self-fertile morph and selection for disassortative pollination in the evolution of morphological distyly.
Abstract: Experiments on pollen flow and seed production were performed in populations of P. vulgaris in order to examine the roles of selection for reduced self-pollination in a partially self-fertile morph, selection for reduced stigma clogging, selection for a pollen saving effect, and selection for disassortative pollination in the evolution of morphological distyly (reciprocal herkogamy). Selection for reduced self-pollination and disassortative pollination were shown to have a plausible role in the evolution of this dimorphism. Selection for reduced stigma clogging and pollen saving appeared to have no obvious role in the evolution of morphological distyly.
TL;DR: Glycine argyrea (Fabaceae), a perennial wild relative of soybean, has a dual flowering strategy of both self-fertilized cleistogamy flowers and chasmogamous flowers on the same plant, providing scope for the operation of selection at different levels.
Abstract: Glycine argyrea (Fabaceae), a perennial wild relative of soybean, has a dual flowering strategy of both self-fertilized cleistogamous flowers and chasmogamous flowers on the same plant. Using allozyme polymorphisms the frequency and pattern of outcrossing was determined. The genotypes of seeds from each of several fruit (legumes) per plant were analysed by starch gel electrophoresis, and the maternal genotype inferred. The maximum likelihood estimates of outcrossing rate for the chasmogamous flowers averaged 0.38. The observed level of heterozygosity in the adult population (h = 0.25) compared with the level expected under random mating (h = 0.32) indicated that partial outcrossing was typical of this population. To analyse the mating pattern further, the pollen genotypes of several seeds per legume for pairs of legumes from the same plant were determined. About 35% of fruit from chasmogamous flowers had no genetically detectable outcross progeny, presumably because they were not cross-pollinated effectively. The majority of the remaining fruit had seed which were of mixed origin (both self-fertilized and outcrossed), suggesting that insect pollination does not preclude self-fertilization. As might be expected from this entomophilous pollination system, the pollen of outcrossed seed within one fruit usually (85% of cross-pollinated legumes) came from one male source. Evidence of pollen carry-over was found in the other legumes. The joint distribution of male sources among the pairs of legumes (paired fruit analysis) showed that non-self sources were shared in 30% of pairs. The probability that two outcrossed seeds from the same fruit would be half-sibs was estimated as 0.15, and for two seeds from different fruit on the same plant as 0.42. There is a hierarchy of genetic identity within and among legumes on the same plant, and on different plants, providing scope for the operation of selection at different levels.
TL;DR: Copulatory organs appear to have high inherent stability, probably resulting from frequent location in strongly homoeostatic environments, single function, insensitivity to niche shift and inertia due to the need to conform to the genitalia of the opposite sex.
Abstract: The structure of copulatory organs is used very widely in systematics, both for differentiating species and for working out relationships. Differences between taxa may arise from a variety of sources, including non-homology, differences in other parts of the animal, direct selection on copulatory organs, development of physical isolating mechanisms and pleiotropic events. Physical isolating mechanisms seem likely to account for the abrupt differences, involving size, asymmetry and simplifications, that are useful in distinguishing very similar lacertid species. Although these differences usually seem to arise at the end of a speciation event they can simultaneously be the initiating mechanism in a second one. Copulatory organs appear to have high inherent stability, probably resulting from frequent location in strongly homoeostatic environments, single function, insensitivity to niche shift and inertia due to the need to conform to the genitalia of the opposite sex. This stability may be overridden at times by direct selection on the organs themselves or pleiotropic events. Such changes tend to be retained because efficiency in copulation depends not on any absolute genital architecture but on close conformity of the organs. It is the combination of relative stability and tangible input of varied change, which tends to be retained, that so often makes these structures good indicators of relationship.
TL;DR: It is suggested that population structure is important in the spread of co-adapted genomes, as well as in their establishment, if there are persistent, wide gradients in Podisma density.
Abstract: A survey was made to determine the shape of the chromosomal cline, between two races of the alpine grasshopper Podisma pedestris, in an area distant from previous detailed studies. The new section was in an isolated mountain block at the western end of the Alpes Maritimes. The past changes in the grasshoppers' distribution can be deduced from a consideration of the history of climatic fluctuations. These distribution changes imply that the hybrid zone has persisted on the isolated mountain block since before the last climatic optimum. The stability of the zone's location can be explained if there are persistent, wide gradients in Podisma density. An assessment of Podisma density revealed suitable gradients. Whilst the cline was generally the same width as in other areas, it was more abrupt where it crossed an inhospitable area, and less well defined in marginal populations. This suggested other interactions between the population density and the dynamics of the racial mixing. The implications of these interactions are discussed. It is suggested that population structure is important in the spread of co-adapted genomes, as well as in their establishment.
TL;DR: Genetic and phenotypic correlations were correlated in the song sparrow, but heritabilities of traits varied greatly, and the genetic variance-covariance matrix for traits is not simply a constant multiple of the phenotypesic matrix.
Abstract: We estimated heritabilities, and genetic and phenotypic correlations between beak and body traits in the song sparrow (Melospiza melodia). We compared these estimates to values for the same traits in the Galapagos finches, Geospiza (Boag, 1983; Grant, 1983). Morphological variance is low in the song sparrow, and our results show that genetic and phenotypic correlations are considerably lower than correlations in the morphologically more variable Geospiza. Comparison using a larger sample of Galapagos populations confirms the existence of an association between variance and correlation for phenotypic values. We suggest two possible explanations for this association. First, most traits studied are functionally related, and the joint evolution of variance and correlation may have resulted from stabilizing selection about a line of optimal allometry between traits. Alternatively, introgression between populations and species could have caused correlation and variance to evolve jointly. Both selection and introgression were probably influential in producing the observed pattern, but it is not possible to estimate their relative importance with current data. Genetic and phenotypic correlations were correlated in the song sparrow, but heritabilities of traits varied greatly. As a result, the genetic variance-covariance matrix for traits is not simply a constant multiple of the phenotypic matrix. Evolutionary response to natural selection cannot, therefore, be predicted from the measurement of phenotypic characteristics alone.
TL;DR: It is argued that mutualism generates positive, interspecific, frequency-dependent selection, which acts as a cohesive evolutionary force, discouraging evolution of specificity, and surveys some data on specificity of mutualisms.
Abstract: It has been argued that mutualisms are non-specific when mutualistic interactions are weak and transient, and become more specific as interactions increase in strength. However, this runs counter to the observation that there exist tightly linked mutualisms of great antiquity that are highly nonspecific. Here we argue that mutualism generates positive, interspecific, frequency-dependent selection, which acts as a cohesive evolutionary force, discouraging evolution of specificity. A simple mathematical model is constructed to analyse the evolution of a community consisting of two guilds of species with mutualistic between-guild interactions, two competing species in each guild and two genetically distinct phenotypes within each species. With some simplifying assumptions, the trajectories in the neighbourhood of the only interior equilibrium point are determined analytically in terms of interactions between individuals. These show that the equilibrium is locally stable (no evolution) when there is little differentiation between phenotypes in mutualistic and interspecific, competitive interactions. On the other hand, when there is strong differentiation between phenotypes in their mutualistic interactions, the equilibrium is unstable and the community starts to evolve towards non-specificity. There are, however, two forces counteracting this tendency which, if sufficiently potent, cause evolution towards specificity. The first is generated by strong differentiation between phenotypes in interspecific competition; the second is caused by specificity which already exists between species in their mutualistic interactions. Thus, the tendency for non-specificity or specificity to evolve depends on the interplay between antagonistic and mutualistic interactions in the community. We illustrate these results with some numerical examples and, finally, survey some data on specificity of mutualisms in the light of the analysis.
TL;DR: The general matching of shell colours to background colours seen in terrestrial gastropods implies that, as in insects, visual predation is an important factor which has a long term directional effect.
Abstract: The general matching of shell colours to background colours seen in terrestrial gastropods implies that, as in insects, visual predation is an important factor which has a long term directional effect. Polymorphism in snails is associated with background heterogeneity, but the causal relation of polymorphism to heterogeneity is not obvious. Predation could maintain polymorphism if predators are frequency dependent in their choice of prey. However, the appropriate predator behaviour does not depend directly on background heterogeneity. An indirect contribution could be that the heterogeneity serves to lower the signal:noise ratio during the predation process. Background heterogeneity could have a direct effect if the background provided specific elements mimicked by the morphs. The remaining diversity could aid the process by lowering the signal:noise ratio. Polymorphism could be maintained if there was frequency-dependent niche selection on the part of prey. Background diversity would then be directly involved. It is necessary that there should be independent control of numbers in the different niches. In warm conditions the niche selection could come about because darker morphs, which gain more radiant heat than paler ones, will move to more cryptic sites by seeking the shade. For morph frequences to approach equilibrium values closely it is necessary for the alleles controlling the polymorphism to exhibit dominance. Differences in received energy could make pale morphs disadvantageous compared with dark ones at low temperatures but advantageous at high ones. In spatially varied temperature conditions a polymorphism could be generated without predation. Density-dependent selection is again required.
TL;DR: Variations among clones in numbers of physiologically independent members and in size and shape of areal extent are discussed in the context of processes that may affect evolution of clonal characters in these populations and in other species that propagate by dispersing asexual fragments.
Abstract: Populations of three branching Caribbean demosponge species are composed of clones produced by asexual fragmentation. Dispersal of the fragments before they become established as independent individuals scatters clone members widely and intermixes members of different clones, complicating study of the clone structure of these populations and contrasting with many other sessile clonal organisms. Clone structures of these populations were inferred using a combination of tissue-compatibility relationships and an analysis of variations in morphology and colour. Although tissue compatibility cannot be used for precise identification of sponge clones, in general, patterns of variation in morphological characters influencing fragmentation and patterns of fragment dispersal and recruitment suggest that, in these populations, tissue-compatibility relationships closely reflect clone structure. Conditions that must be met in order to use tissue compatibility for study of sponge clones are discussed, and previous results, from which conflicting conclusions have been drawn, reconciled in this context. Variations among clones in numbers of physiologically independent members and in size and shape of areal extent are discussed in the context of processes that may affect evolution of clonal characters in these populations and in other species that propagate by dispersing asexual fragments.