Showing papers in "Biological Journal of The Linnean Society in 1991"
TL;DR: Metapopulation studies have important conceptual links with the equilibrium theory of island biogeography and with studies on the dynamics of species living in patchy environments as mentioned in this paper, and they play an increasingly important role in landscape ecology and conservation biology.
Abstract: We review the early development of metapopulation ideas, which culminated in the well-known model by Levins in 1969. We present a survey of metapopulation terminology and outline the kinds of studies that have been conducted on single-species and multispecies metapopulations. Metapopulation studies have important conceptual links with the equilibrium theory of island biogeography and with studies on the dynamics of species living in patchy environments. Metapopulation ideas play an increasingly important role in landscape ecology and conservation biology.
1,537 citations
TL;DR: A modified view of metapopulation dynamics is suggested, in which local extinction is more an incidental than a central feature and regional persistence depends critically upon parameters influencing extinction and colonization rates.
Abstract: Metapopulations are classically viewed as sets of populations persisting in a balance between local extinction and colonization. When this is true, regional persistence depends critically upon parameters influencing extinction and colonization rates, e.g. the number of habitat patches and populations, the rates and patterns of interpatch migration, and propagule establishment probabilities. A review of relevant empirical literature identifies few metapopulations which fit this description well. Instead, three qualitatively different situations are found to be more common: (1) mainland-island and source-sink metapopulations, in which persistence depends on the existence of one or more extinction-resistant populations; (2) patchy populations, in which dispersal between patches or sub-populations is so high that the system is effectively a single extinction-resistant population; (3) non-equilibrium metapopulations, in which local extinction occurs in the course of a species' overall regional decline. This suggests a modified view of metapopulation dynamics in which local extinction is more an incidental than a central feature.
921 citations
TL;DR: Characteristics of dispersal that influence metapopulation functioning, such as releasing factors, density dependence, timing and types and health of dispersers, are reviewed.
Abstract: This paper reviews characteristics of dispersal that influence metapopulation functioning, such as releasing factors, density dependence, timing and types and health of dispersers. Economic thresholds, intraspecific conflicts and avoidance ofinbreeding are often regarded as the key ultimate or proximate (or both) causes of dispersal, but there is no consensus aboutthe most important mechanisms. Dispersing individuals are often considered to differ genetically from the residents but goodsupporting evidence has only been presented for some insect species. Sex and age differences in dispersal rates are mostcommon in polygamous species and in long-lived species with many litters per female. A bimodal distribution of dispersaldistances, earlier thought to be a common pattern, is probably an artifact, caused by habitat heterogeneity and varyingsurvival of settled individuals. Dispersal distances are longer in poor environments. Habitat specialists are more affected byboundaries during dispersal than generalists. Dispersal just before or during the early reproductive season is common incertain species occupying early successional habitats. Dispersal increased both population and metapopulation size andpersistence in plants, insects and small mammals.
295 citations
TL;DR: Connectivity is concluded to be a key to metapopulation persistence not just in terms of recolonization, but also for populations fluctuate more greatly in size than predicted from demographic models which have been commonly referred to.
Abstract: Local extinction along the intrinsic isolation gradient within metapopulations is reviewed with particular referenceto a study of the pool frog ( Rana lessonae ) on the northern periphery of its geographical range. As inthe pool frog, many other different taxa show significantly increased extinction probabilities with increased interpopulationdistance. Present data imply that the relative impact of demographic and genetic factors in such stochastic extinctionsdepends on the genetic history of the metapopulation; data also imply that populations fluctuate more greatly in size thanpredicted from demographic models which have been commonly referred to. By mitigating such fluctuations and inbreeding, andcompensating for emigration, immigration undoubtedly “rescues” local populations from extinction. In this way, andnot just in terms of recolonization, connectivity is concluded to be a key to metapopulation persistence. Implications forconservation are also presented.
295 citations
TL;DR: The structure of a population over time, space and categories of social and sexual role governs its ability to retaingenetic variation in the face of drift, and the ability of a metapopulation to retain genetic variation can be one to two orders of magnitude lower than themaximum total number of individuals in the system.
Abstract: The structure of a population over time, space and categories of social and sexual role governs its ability to retaingenetic variation in the face of drift. A metapopulation is an extreme form of spatial structure in which loosely coupledlocal populations “turnover”, that is, suffer extinction followed by recolonization from elsewhere within themetapopulation. These local populations turn over with a characteristic half-life. Based on a simulation model thatincorporates both realistic features of population ecology and population genetics, the ability of such a metapopulation toretain genetic variation, which may be defined as proportional to its so-called effective population size, denoted N c (meta) , can be one to two orders of magnitude lower than themaximum total number of individuals in the system. N c (meta) dependson the persistence time associated with longevity of local populations (the turnover half-life), the average number of localpopulations extant in the metapopulation and the gene flow between local populations. Habitat fragmentation, which can createa metapopulation from a formerly continuously distributed species, may have unappreciated large genetic consequences forspecies impacted by human development.
290 citations
TL;DR: In this article, the use of the epithet "adaptive" in the popular denotation 'adaptive radiation' suggests that radiation as such does not imply adaptation, and emphasis is given to what might be called nonadaptively radiation, a kind of diversification not accompanied by adaptation into various significantly different niches and, therefore, resulting in a group of allopatric species which are isolated because of competitive interactions.
Abstract: The use of the epithet ‘adaptive’ in the popular denotation ‘adaptive radiation’ suggests that radiation as such does not imply adaptation. Without trying to define radiation more sharply than is usually done in textbooks, emphasis is given to what might be called non-adaptive radiation, a kind of diversification not accompanied by adaptation into various significantly different niches and, therefore, resulting in a group of allopatric species which are isolated because of competitive interactions.
268 citations
TL;DR: The consequences of forest fragmentation for the dynamics of bird populations are reviewed, showing how fine-grained fragmentation triggers distance-area and landscape effects on alocal scale, which results in a range retraction of a population to non-fragmented or less fragmented parts of aregion.
Abstract: This paper reviews the consequences of forest fragmentation for the dynamics of bird populations. Owing to highmobility and large home ranges, birds usually perceive fragmented forests in a finegrained manner, i.e. embrace several forest fragments in functional home ranges. On a regional scale, however, coarse-grained clusters of fine-grained fragments(hierarchical fragmentation may sub-divide bird populations into isolated demes, which enter a domain of metaPopulation dynamics. Distinctions are made between pure distance-area or population-level effects and more indirect community-leveleffects due to changes in landscape composition. Distance-area effects, such as insularization and decreasing fragment size, directly prevent dispersal and reduce population size. Landscape effects, such as reduced fragment-matrix and interior-edgeratios, increase the pressure from surrounding predators, competitors, parasites and disease. In short, forest fragmentationcan be viewed as a two-step process. Initially, fine-grained fragmentation triggers distance-area and landscape effects on alocal scale, which in turn, results in a range retraction of a population to non-fragmented or less fragmented parts of aregion. At a certain point, non-fragmented areas become so widely spaced out that regional distance-area effects come intooperation, giving rise to metapopulation dynamics. Although few bird metapopulations have yet been documented, metaPopulation dynamics probably is a common characteristic of bird populations confined to “hierarchical” fragmentedforests.
239 citations
TL;DR: Strong interlocus genotypic associations suggest that selection against hybrids is intense in later generations; the c.
Abstract: Populations of the common mussel (Mytilus edulis) from the North Sea area (Skakerrak-Kattegat) and those from the Baltic Sea are almost diagnostically differentiated at five out of 22 studied allozyme loci; at a further seven loci, alleles predominant or common in one area are nearly absent in the other. Genetic distance was estimated at 0.28; this is similar to the distances of these populations to the Mediterranean mussel M. galloprovincialis. The three mussel types obviously represent equal evolutionary divergence from one another, and should also be taxonomically equally separated; a semispecies rank within a more comprehensive M. edulis complex or superspecies is suggested. The age of the Baltic mussel type (‘M. trossulus’), as an independent evolutionary lineage, is probably far greater than that of the post-glacial Baltic Sea.
Allele frequencies change gradually and in parallel when entering from the Kattegat through the Sound into the Baltic. Only a slight Wahlund effect at the strongly diverged Gpi and Pgm loci was found in intermediate populations, indicating that extensive hybridization of the two taxa takes place in the area. However, strong interlocus genotypic associations suggest that selection against hybrids is intense in later generations; the c. 100 km wide hybrid zone is narrow relative to the dispersal distance. The genotypic structure of the Lap locus does not conform with those of the other loci studied in the hybrid zone; it cannot be viewed merely as a neutral marker of the process of hybridization.
188 citations
TL;DR: It is determined that habitat explains some of the variation in call structure; this is not true of subspecies; the hypothesis that some differences in calls among habitats result from environmental selection on call structure to enhance call transmission is supported.
Abstract: Advertisement calls of the cricket frog, Acris crepitans, show statistically significant variation among populations in all call variables measured. Call variables show strong clinal variation resulting in calls of lower frequency, longer duration and slower call rates produced by A. c. blanchardi in open habitat in the west of the range, and calls of higher frequency, shorter calls and faster call rates produced by A. c. crepitans in the pine forests in the eastern part of the range. This clinal variation does not result from pleiotropic effects of body size or any other morphological characters we measured.
The two subspecies usually reside in different habitats, but some A. c. blanchardi reside in an isolated pine forest in central Texas. By comparing the calls of this subspecies in open and forest habitat, and by statistically removing the effects of clinal variation for all populations, we determined that habitat explains some of the variation in call structure; this is not true of subspecies.
Our data reject several hypotheses that purport to explain the evolution of mate recognition signals. (1) We reject the notion of Paterson and others that there is strong stabilizing selection on species-specific mate recognition signals. (2) There is no support for the hypothesis that call variation is primarily due to pleiotropic effects of body size or other morphological characters over the geographic range we examined. (3) There is no evidence for reproductive character displacement. (4) Our data, as well as experimental studies of habitat acoustics, support the hypothesis that some differences in calls among habitats result from environmental selection on call structure to enhance call transmission. We suggest that the latter hypothesis does not explain the strong clinal component of call variation. This might result from the passive effects of gene flow between populations at the extremes of the range under selection generated by habitat acoustics.
174 citations
TL;DR: A logical framework for an island-biogeographic theory based on species interactions and invasions and for the protection of fragile native species from invading exotics is provided.
Abstract: Islands or habitat patches in a metapopulation exist as multi-species communities. Community interactions link eachspecies' dynamics so that the colonization of one species may cause the extinction of another. In this way, communityinteractions may set limits to the invadability of an island and to the likelihood of resident species extinctions uponinvasion. To examine the nature of these limits, I assemble stable multi-species Lotka-Volterra competition communities thatdiffer in resident species number and the average strength (and variance) of species interactions. These are then invaded withspecies whose properties are drawn from the same distribution as the residents. The invader success rate and the extinctionrate of resident species is determined as a function of community- and species-level properties. I show that the probabilityof colonization success for an invader decreases with species number and the strength and variance of interspecificinteractions. Communities comprised of many strongly interacting species limit the invasion possibilities of competingspecies. Community interactions, even for a superior invading competitor, set up a sort of “activation barrier”that repels the invader. This “priority effect” for residents is not assumed a priori in mydescription for the individual population dynamics of these species, rather it arises because species-rich andstrongly-interacting species sets have alternative stable states that tend to disfavour species at low densities. These modelspoint to community-level rather than invader-level properties as the strongest determinant of differences in invasion success.If an invading species is successful it competitively displaces a greater number of resident species, on average, as communitysize increases. These results provide a logical framework for an island-biogeographic theory based on species interactions andinvasions and for the protection of fragile native species from invading exotics.
173 citations
TL;DR: It is concluded that inquiline species strictly following Emery's rule could have evolved by the intraspecific route, and such species provide evidence for West-Eberhard's “alternative adaptation” hypothesis that between-species diversity frequently stems from diversity within species.
Abstract: Inquiline ant species are workerless social parasites whose queens reproduce in colonies of other species alongside the host queens. Inquilines arise either when one non-parasitic species evolves into an inquiline parasite of another non-parasitic species (the interspecific hypothesis), or by the speciation of intraspecific inquilines from their host stock (the intraspecific hypothesis): it is unlikely that inquilines evolve from other forms of social parasite. This paper reviews the evidence for and against the inter-and intraspecific hypotheses. All inquilines are close phylogenetic relatives of their host species (loose ‘Emery's rule’), and some are their host's closest relative (strict ‘Emery's rule’). A problem for the interspecific hypothesis is how to explain the strict Emery's rule, because phylogenetic constraints on host choice are probably quite weak. By contrast, the intraspecific hypothesis has difficulty accounting for the parasites' sympatric reproductive isolation.
Facultative polygyny, in which queens may found colonies alone or by adoption into an existing multi-queen colony, should promote the evolution of small intraspecific inquilines. This is because small colony-founding queens should preferentially seek adoption, which provides the opportunity to produce a sexual-only brood. We suggest that microgynes, i.e. miniature queens found in some polygynous ants, represent such parasites. We review the evidence that inquiline species have evolved intraspecifically from microgynes in Myrmica ants. The coexistence within a species of a monogynous (singly-queened) and a polygynous form is probably a phenomenon usually unconnected with inquiline evolution.
The reproductive isolation of intraspecific inquilines plausibly arises from divergent breeding behaviour associated with the parasites' small size. Such divergence could involve either a temporal separation in mating episodes, with small parasites maturing early, or a spatial separation, with small males being sexually-selected to mate near the nest with small queens seeking adoption, instead of in mating aggregations.
We conclude that inquiline species strictly following Emery's rule could have evolved by the intraspecific route. If so, such species provide evidence for West-Eberhard's “alternative adaptation” hypothesis that between-species diversity frequently stems from diversity within species. They also represent likely cases of sympatric speciation. We suggest work on the parasites' phytogeny, genetics, behaviour and mating biology to test these conclusions further.
TL;DR: Conspecific attraction is incorporated into two metapopulation models which differ in type of dispersal, the Levins model and atwo-dimensional stepping-stone model, which lowers the proportion of occupied habitat patches within a metAPopulation at equilibrium.
Abstract: Random dispersal direction is assumed in all current metapopulation models. This assumption is called into questionby recent experiments demonstrating that some species disperse preferentially to sites occupied by conspecifics. Weincorporate conspecific attraction into two metapopulation models which differ in type of dispersal, the Levins model and atwo-dimensional stepping-stone model. In both models, conspecific attraction lowers the proportion of occupied habitat patcheswithin a metapopulation at equilibrium.
TL;DR: Although a few non-ponerine species exhibit some of these preconditions, gamergates have not been found outside the Ponerinae, which alone exhibit the combination of traits leading to queen elimination and worker mating.
Abstract: In less than 100 species of ponerine ants, queens no longer exist and have been replaced by mated egg-laying workers. Workers in other subfamilies can lay haploid eggs when queens are removed, but they never reproduce sexually. Ponerine workers are able to mate because they have a spermatheca in most species, foreign males are sexually active near their nests, and their pygidial gland secretions can assume a sexual meaning. Furthermore, ponerine queens are seldom very fecund, and one or several gamergates are able to approximate their egg production. Finally, opportunities for colony fragmentation occur consequent to their life history, and this is a necessary precondition because gamergates cannot start new colonies independently. Many of these characteristics are associated with the limited caste divergence exhibited in this phylogenetically primitive group. Although a few non-ponerine species exhibit some of these preconditions, gamergates have not been found outside the Ponerinae, which alone exhibit the combination of traits leading to queen elimination and worker mating.
TL;DR: The Hemiptera fauna of a moderately large and topographically diverse area of tropical rain forest in Sulawesi Utara, Indonesia is presented and the global estimates of 1.84–2.57 million species of insect are much lower than the 10–80 million predicted by Erwin and Stork from a study of tropical Coleoptera.
Abstract: Data are presented on the Hemiptera fauna of a moderately large and topographically diverse area of tropical rain forest in Sulawesi Utara, Indonesia. Insects were sampled using several methods at several sites over a 1-year period. The numbers of described and undescribed species captured is used to predict the number of extant species of both Hemiptera and total insects in the world. The global estimates of 1.84–2.57 million species of insect are much lower than the 10–80 million predicted by Erwin and Stork from a study of tropical Coleoptera. The reasons for believing that the lower estimates are more reliable are discussed.
TL;DR: The effects of predation in mediating coexistence among competing prey species is examined and three models for interspecific competition are considered; if the species are identified with early and late successional species, the models describe the facilitation, inhibition and tolerance models of ecological succession.
Abstract: Metapopulation diversity patterns depend on the relations among the timescales of local biological interactions (predation, competition), the rates of dispersal among local populations and the patterns of disturbance. We investigate these relationships using a family of simple non-linear Markov chain models. We consider three models for interspecific competition; if the species are identified with early and late successional species, the models describe the facilitation, inhibition and tolerance models of ecological succession. By adding a third competing species we also compare transitive competitive hierarchies and intransitive competitive networks. Finally, we examine the effects of predation in mediating coexistence among competing prey species. In each model we find circumstances in which biotic or abiotic disturbance can increase both local and regional diversity, but those circumstances depend on the various timescales in the model in ways that arc neither obvious nor trivial.
TL;DR: Three morphotypes of brown trout from Lough Melvin in north-west Ireland are described and it has been shown that the three types maintain their genetic integrity as the result of their distinctive spawning habits.
Abstract: Three morphotypes of brown trout have been described from Lough Melvin in north-west Ireland: gillaroo; sonaghen; ferox. The extensive genetic differences among the three types indicate that they are reproductively isolated, i.e. separate stocks of trout. For example, only gillaroo possess the Ldh-1(n) allele. Ferox show a high frequency of the Ldh-5(100) allele and this allele does not exceed a frequency of 0.02 in the other two types. Sonaghen are characterized by relatively much higher frequencies for Ck-2(115) and Gpi-2(135) alleles. Sampling over a period of 7 years and experiments with artificial stocks of gillaroo and sonaghen have demonstrated that these differences are temporally stable. On the basis of observation of mature adults and the genetic composition of fry samples, it has been shown that the three types maintain their genetic integrity as the result of their distinctive spawning habits with gillaroo spawning in the lake and outflowing river, sonaghen in the smaller inflowing rivers and ferox in the deep downstream section of the largest inflowing river. The ferox is a relict population of an early post-glacial trout colonist while gillaroo and sonaghen are representative of a more recent independent colonization. However, it cannot be determined at present whether or not gillaroo and sonaghen were already differentiated prior to colonizing Melvin although the weight of evidence favours a sympatric split. It is proposed that the three types of trout be designated as separate subspecies to highlight the need for independent management and urgent requirement for conservation action.
TL;DR: By representing the growth phase as a simple presence/absence state of a patch, metapopulation dynamics can be bedescribed by a system of ordinary differential equations with the classic Lotka-Volterra model as a limiting case.
Abstract: Many arthropod predator-prey systems on plants typically have a patchy structure in space and at least two essentially different phases at each of the trophic levels: a phase of within-patch population growth and a phase of between-patch dispersal. Coupling of the trophic levels takes place in the growth phase, but it is absent in the dispersal phase. By representing the growth phase as a simple presence/absence state of a patch, metapopulation dynamics can be described by a system of ordinary differential equations with the classic Lotka-Volterra model as a limiting case (e.g. when the dispersal phases are of infinitely short duration). When timescale arguments justify ignoring plant dynamics, it is shown that the otherwise unstable Lotka-Volterra model becomes stable by any of the following extensions: (1) a dispersal phase of the prey, (2) variability in prey patches with respect to the risk of detection by predators, (3) (sufficiently high) interception of dispersing predators in predator-invaded prey patches, and (4) prey dispersal from predator-invaded prey patches. The parameter domain of stability shrinks when the duration of within-patch predator-prey interaction is fixed rather than variable, and when predators do not disperse from a patch until after prey extermination. A dispersal phase of the predator has a destabilizing effect in contrast to a dispersal phase of the prey. When the timescale of plant dynamics is not very different from predator-prey patch dynamics, the Lotka-Volterra predator-prey patch model should be extended to a predator-prey-plant patch model, but this greatly modified the list of potential stabilizing mechanisms. Several of the mechanisms that have a stabilizing effect on a ditrophic model lose this effect in a tritrophic model and may even become destabilizing; for example, the dispersal phase of the prey confers stability to the predatory-prey model, but destabilizes the steady state in the predator-prey-plant model in much the same way as the dispersal phase of the predator destabilizes the steady state in the predator-prey model. Other mechanisms retain their stabilizing effect in a tritrophic context; for example, dispersal of prey from predator-invaded prey patches has a stabilizing effect on both predator-prey and predator-prey-plant models.
TL;DR: Populations of the guppy Poecilia reticulata from six locations in N.E. Trinidad were examined by starch gel electrophoresis to estimate their degree of genetic divergence, and patterns of population differentiation are discussed in relation to probable past geological and historical events, and present-day evolutionary forces.
Abstract: Populations of the guppy Poecilia reticulata from six locations in N. Trinidad were examined by starch gel electrophoresis to estimate their degree of genetic divergence. Variability at seven enzyme-coding loci demonstrated that populations differed markedly in allele frequencies with some allelic substitution between sites (for 23 loci, Nei's mean genetic identity, Ī ranged from 0.869–1.00; the coefficient of gene differentiation, GST= 0.086; and the absolute differentiation between populations, Dm= 0.044). There was a good correspondence between degree of physical isolation and extent of genetic differentiation, as exemplified by the partitioning of gene diversity (Nei's gene diversity analysis = 66% between river basins; 32% within river basins; 2% within rivers), though there was considerable variability in the contribution of individual loci. Most populations were in Hardy-Weinberg equilibrium, and any significant deviations were due exclusively to heterozygote deficiencies. The patterns of population differentiation are discussed in relation to probable past geological and historical events, and present-day evolutionary forces. Notable among these are previous continental land connections, periodic immigration from N.E. South America, and post-colonization events including differential predation, sexual selection, apparent restricted vagility and small effective population sizes.
TL;DR: I develop models of metapopulation dynamics that describe changes in the numbers of individuals within patches, analogous to structured population models, with patches playing the role of individuals.
Abstract: I develop models of metapopulation dynamics that describe changes in the numbers of individuals within patches. These models are analogous to structured population models, with patches playing the role of individuals. Single species models which do not include the effect of immigration on local population dynamics of occupied patches typically lead to a unique equilibrium. The models can be used to study the distributions of numbers of individuals among patches, showing that both metapopulations with local outbreaks and metapopulations without outbreaks can occur in systems with no underlying environmental variability. Distributions of local population sizes (in occupied patches) can vary independently of the total population size, so both patterns of distributions of local population sizes are compatible with either rare or common species. Models which include the effect of immigration on local population dynamics can lead to two positive equilibria, one stable and one unstable, the latter representing a threshold between regional extinction and persistence.
TL;DR: An extensive survey of isozyme phenotypes in British populations of the amphidiploid salt marsh grass Spartina anglica and its putative parents has confirmed that the species arose by chromosome doubling in S. × townsendii, a sterile hybrid between S. maritima and S. alterniflora.
Abstract: An extensive survey of isozyme phenotypes in British populations of the amphidiploid salt marsh grass Spartina anglica and its putative parents has confirmed that the species arose by chromosome doubling in S. × townsendii, a sterile hybrid between S. maritima and S. alterniflora. Isozyme phenotypes and seed protein profiles indicate that S. anglica is almost totally lacking in genetic variation. Isozyme evidence also indicates that the parental species are characterized by low levels of genetic variation. The lack of variation in S. anglica is proposed as being due to a narrow genetic base resulting from a single origin, or a multiple origin from uniform parents; the fact that many populations are derived from very small founder populations; and because preferential pairing between identical homologous chromosomes prevents recombination between the divergent component genomes of the species. The low levels of isozyme variation that occur appear to be due to chromosome loss.
The consequences for the future evolution of S. anglica, given its lack of genetic variation, are discussed.
TL;DR: Exinction models as well as empirical data suggest that a large propagule with a potential for rapid increase in a varying environment, or with a low mortality rate in an environment perceived as constant, has a higher probability of successful colonization.
Abstract: In metapopulation dynamics turnover of populations in isolated patches may be frequent. Regional survival of aspecies in such a system with frequent extinctions hinges on its colonization ability. Colonization is more than justdispersal; when a propagule reaches a new patch it faces higher extinction probabilities than does an established population. Extinction models as well as empirical data suggest that a large propagule with a potential for rapid increase in a varyingenvironment, or with a low mortality rate in an environment perceived as constant, has a higherprobability of successful colonization. Large variation in population size when it is still small increases the risk offailure. Factors introducing such variation are demographic stochasticity and environmental variation. It is hard to singleout demographic traits that ensure good colonizing ability, since colonization can be achieved in many different ways, butgeneralists and species with self-fertilization seem to be superior.
TL;DR: Among the aspects to be examined are the behaviour of different culture systems when exposed to ultralow temperatures, crop-specific requirements and the genetic stability of stored material.
Abstract: In-vitro (tissue culture) techniques offer ways of overcoming serious problems in the conservation of crop genetic resources. These primarily involve the use of slow growth and cryopreservation in liquid nitrogen to store germplasm, but there are also important applications in other areas, including germplasm collecting, multiplication and exchange. Slow growth techniques for medium-term storage of cultures are relatively well developed and in-vitro active gene bank establishment is feasible. Cryopreservation for long-term storage is possible for some materials but, in general, requires further research and development. Among the aspects to be examined are the behaviour of different culture systems when exposed to ultralow temperatures, crop-specific requirements and the genetic stability of stored material.
TL;DR: Possession of extrafloral nectaries does not appear to be essential for the development of symbiotic ant-plant interactions, and a comparison with other euphorb species living in the same habitats as Macaranga showed that in genera in which extrafloras are widespread, no myrmecophytes have evolved.
Abstract: Some species of the paleotropical tree genus Macaranga (Euphorbiaceae) live in close association with ants. The genus comprises the full range of species from those not regularly inhabited by ants to obligate myrmecophytes. In Malaysia (Peninsular and Borneo) 23 of the 52 species are known to be ant-associated (44%). The simplest structural adaptation of plants to attract ants are extrafloral nectaries. We studied the distribution of extrafloral nectaries in the genus Macaranga to assess the significance of this character as a possible predisposition for the evolution of obligate myrmecophytism. All species have marginal glands on the leaves. However, only the glands of non- myrmecophytic species function as nectaries, whereas liquids secreted by these glands in myrmecophytic species did not contain sugar. Some non-myrmecophytic Macaranga and transitional Macaranga species in addition have extrafloral nectaries on the leaf blade near the petiole insertion. All obligatorily myrmecophytic Macaranga species, however, lack additional glands on the lamina. The non-myrmecophytic species are visited by a variety of different ant species, whereas myrmecophytic Macaranga are associated only with one specific ant-partner. Since these ants keep scale insects in the hollow stems, reduction of nectary production in ant-inhabited Macaranga seems to be biologically significant. We interpret this as a means of (a) saving the assimilates and (b) stabilization of maintenance of the association's specificity. Competition with other ant species for food rewards is avoided and thereby danger of weakening the protective function of the obligate ant- partner for the plant is reduced.
A comparison with other euphorb species living in the same habitats as Macaranga showed that in genera in which extrafloral nectaries are widespread, no myrmecophytes have evolved. Possession of extrafloral nectaries does not appear to be essential for the development of symbiotic ant-plant interactions. Other predispositions such as nesting space might have played a more important role.
TL;DR: The European badger is taken as an example to illustrate that the stochastic Levins model can form a satisfactory description for populations of real animals, even for those with complex social behaviour.
Abstract: Stochastic models for metapopulations that consist of a finite number of local populations are discussed. A stochastic Levins model with two local slates (metapopulation level: a patch is occupied or empty) is compared with a detailed model at the level of local populations. The European badger is taken as an example to illustrate that the stochastic Levins model can form a satisfactory description for populations of real animals, even for those with complex social behaviour. The local population model is a Markov chain model with animals of two sexes and a 1-year reproduction cycle. Both heuristic and mathematical arguments are given to show that the stochastic Levins model is a sufficiently accurate representation of the complex model. A more general application of this modelling strategy is suggested (or bird and mammal species with a fragmented distribution, yielding a tool for evaluating conservation measures for species threatened by fragmentation. The local population model can then be used to translate changes in population parameters (birth, death, dispersal) into processes on the metapopulation level (local extinction, colonization).
TL;DR: Observations and literature records indicate that ant taxa which tend butterfly larvae are the same taxa that tend extrafloral nectaries and Homoptera, and hence, ant-larval mutualisms.
Abstract: A facultative mutualism between the riodinid butterfly Thisbe ircnca and the ponerine ant Ectafomma ruidurn is described from Panama. Ants protect larvae against attacks of predatory wasps, but not against tachinid parasitoids. Several potential sources of ecological variation affecting the larval survival of Thisbe irenea are noted. A preliminary means of testing the ability of larvae to appease ants is described that may be applied to all butterfly-ant systems. Observations and literature records indicate that ant taxa which tend butterfly larvae are the same taxa that tend extrafloral nectaries and Homoptera. A general hypothesis for the evolution of myrmecophily among butterflies suggests that ant taxa which utilize secretions in their diet are major selective agents for the evolution of the larval ant-organs, and hence, ant-larval mutualisms. This idea is extended to suggest how appeasement of predaceous ant taxa through the use of larval ant-organs can influence an ant-larval relationship, eventually leading to mutualism.
TL;DR: The conditions for the evolution of andromonoecy and male-function-controlled overproduction of fertile flowers in hermaphrodites are considered using the evolutionarily stable strategy (ESS) approach.
Abstract: The conditions for the evolution of andromonoecy and male-function-controlled overproduction of fertile flowers in hermaphrodites are considered using the evolutionarily stable strategy (ESS) approach. Andromonoecy and male-function-controlled floral display are promoted if further increase in pollen amount per flower is disadvantageous and/or increase in the number of polliniferous units is advantageous; the costs of attractive organs and pollen per flower are relatively low while the cost of ovules per flower and the cost per fruit are relatively high; the probability of setting a fruit from a pistillate flower is high; male fertility increases with the resources devoted to flowering; and if selfing is relatively low. Assumptions and predictions of the model are discussed.
TL;DR: It is concluded that interspecific competition is important for the distributional dynamics of Daphnia species in rockpools, but the question whether the coexistence of these species depends on metapopulation dynamics is still unresolved.
Abstract: The assumptions and predictions of metapopulation models for competing species are discussed in relation to empirical studies of colonization and extinction in metapopulations. In three species of Daphnia in rockpools, interspecific competition increased local extinction rates, while no effects on colonization rates were detected. Distributional patterns were consistent with several predictions of the competition model; for example, the number of species on an island increased with the number of pools and the proportion of pools occupied by each species decreased with increasing species number. It is concluded that interspecific competition is important for the distributional dynamics of Daphnia species in rockpools, but the question whether the coexistence of these species depends on metapopulation dynamics is still unresolved. Other studies on the effects of interspecific competition on colonization and extinction rates are discussed.
TL;DR: This work reviews 13 possible examples of predator-prey systems persist, despite unstable local interactions, due to metapopulation processes: movement of individuals among largely independent local populations and discusses the advantages and disadvantages of these methods, as well as alternatives.
Abstract: It has been suggested that many predator-prey systems persist, despite unstable local interactions, due tometapopulation processes: movement of individuals among largely independent local populations. I review 13 possible examplesof this phenomenon all I could find in the literature—and find that each either lacks convincing data or is not a truemetapopulation. Most of the examples rely on evidence of local extinction and recolonization, only a few using directexperimental methods; I discuss the advantages and disadvantages of these methods, as well as alternatives.
TL;DR: Facultative necrophagy in Trigona probably became obligate due to preadaptations including massive forager recruitment via pheromone trails; aggressive foraging on carrion exudates; rapid location of novel resources; beneficial microbes in bee glandular secretions that metabolize protein and produce antibiotics; and queen cells and food storage pots of the same size and close proximity.
Abstract: A systematic revision and biological account is given of the only apoid obligate necrophages, the Trigona hypogea group, along with descriptions of Trigona necrophaga sp. nov. and the male of Trigona crassipes. Trigona necrophaga is endemic to eastern Panama and possibly the Choco; T. hypogea and T. crassipes are sympatric throughout the Amazon Basin and the Guianas. The lack of a corbicula on the hind leg and reduction of giant setae on the labial palpi, workers foraging upon carrion, lack of stored pollen in nests, and complete absence of pollen grains in larval provisions demonstrate obligate necrophagy in all three social, stingless bee species. Evolution of T. hypogea and T. crassipes from a common ancestor in the Amazon Basin is postulated, and T. necrophaga is likely to be an offshoot of T. crassipes. Morphology links T. crassipes and T. hypogea, but nest architecture joins necrophaga and crassipes. Facultative necrophagy in Trigona probably became obligate due to preadaptations including (1) massive forager recruitment via pheromone trails; (2) aggressive foraging on carrion exudates; (3) apical mandibular teeth; (4) rapid location of novel resources; (5) beneficial microbes in bee glandular secretions that metabolize protein and produce antibiotics, and (6) queen cells and food storage pots of the same size and close proximity. Accidental placement of regurgitated, partly-digested carrion in queen cells may have promoted admixture of hypopharyngeal glandular secretions and microbes with harvested liquid carrion. The most derived species, T. necrophaga, may have additional mutualist microbes because only this species has distinctive grey-green protein, and five Bacillus species in food pots and brood cells. No unusual anatomical features were found in worker bees. All three species make sweet, clear honey that contains some pollen but is of unknown origin.
TL;DR: It is suggested that plant-animal interactions have been overemphasized and competitive interactions largely overlooked, as determinants of the Cretaceous revolution in plant history.
Abstract: The rise to dominance of the angiosperms is frequently considered to be directly or indirectly due to co-evolutionary mutualisms with vertebrate seed dispersers and insect pollinators (‘reproductive co-evolution hypothesis’). The decline of the gymnosperms is considered to be due to the inefficiency of wind pollination in maintaining heterozygosity in angiosperm-enriched communities or the limited scope for speciation of wind-pollinated taxa. Contrasting hypotheses for the rise of the angiosperms focus on either environmental change or superior reproductive and vegetative innovations leading to faster growth rates.
We suggest that plant-animal interactions have been overemphasized and competitive interactions largely overlooked, as determinants of the Cretaceous revolution in plant history.