Investigating the independent evolution of the size of floral organs via G-matrix estimation and artificial selection

The attractiveness of a plant to pollinators is dependent on both the number of flowers produced and the size of the petals. However, limiting resources often result in a size/number trade-off, whereby the plant can make either more flowers or larger flowers, but not both. If developmental genes underlying sepal and petal identity (some of which overlap) also influence size, then this shared genetic basis could constrain the independent evolution of floral size and attractiveness. Here, we determined whether the size of sepals and petals in the dioecious perennial, Silene latifolia, are developmentally independent by performing two experiments: a genetic variance-covariance experiment to estimate genetic correlations between calyx width, petal-limb length, flower mass, and number and a four-bout artificial-selection experiment to alter calyx width and estimate the correlated response in petal-limb length. In addition, we determined whether variation in petal-limb length is the result of cell expansion or cell proliferation. The first experiment revealed that petal-limb length is not genetically correlated with calyx width, and the second experiment confirmed this; selection on calyx width did not result in a predictable or significant change in petal-limb length. Flower number was negatively correlated with all the floral traits measured, indicating a flower size/number trade-off. Cell number, but not size, explained a significant amount of the variation in petal-limb length. We conclude that the size of the two outer floral organs can evolve independently. This species can therefore increase the number of flowers produced by decreasing investment in the calyx without simultaneously decreasing petal size and the attractiveness of each individual flower to pollinators.     

Support for the predictions of the pollinator-mediated stabilizing selection hypothesis

Aims Floral traits are frequently used in traditional plant systematics because of their assumed constancy. One potential reason for the apparent constancy of flower size is that effective pollen transfer between flowers depends on the accuracy of the physical fit between the flower and pollinator. Therefore, flowers are likely to be under stronger stabilizing selection for uniform size than vegetative plant parts. Moreover, as predicted by the pollinator-mediated stabilizing selection (PMSS) hypothesis, an accurate fit between flowers and their pollinators is likely to be more important for specialized pollination systems as found in many species with bilaterally symmetric (zygomorphic) flowers than for species with radially symmetric (actinomorphic) flowers.Methods In a comparative study of 15 zygomorphic and 13 actinomorphic species in Switzerland, we tested whether variation in flower size, among and within individuals, is smaller than variation in leaf size and whether variation in flower size is smaller in zygomorphic compared to actinomorphic species.Important findings Indeed, variation in leaf length was significantly larger than variation in flower length and width. Within-individual variation in flower and leaf sizes did not differ significantly between zygomorphic and actinomorphic species. In line with the predictions of the PMSS, among-individual variation in flower length and flower width was significantly smaller for zygomorphic species than for actinomorphic species, while the two groups did not differ in leaf length variation. This suggests that plants with zygomorphic flowers have undergone stronger selection for uniform flowers than plants with actinomorphic flowers. This supports that the relative uniformity of flowers compared to vegetative structures within species, as already observed in traditional plant systematics, is, at least in part, a consequence of the requirement for effective pollination.     

Attracting pollinators and avoiding herbivores: insects influence plant traits within and across years

Perennial plants interact with herbivores and pollinators across multiple growing seasons, and thus may respond to herbivores and pollinators both within and across years. Joint effects of herbivores and pollinators influence plant traits, but while some of the potential interactions among herbivory, pollination, plant size, and plant reproductive traits have been well studied, others are poorly understood. This is particularly true for perennial plants where effects of herbivores and pollinators may manifest across years. Here, we describe two experiments addressing the reciprocal interactions of plant traits with herbivore damage and pollination across 2 years using the perennial plant Chamerion angustifolium. We measured (1) plant responses to manipulation of damage and pollination in the year of treatment and the subsequent season, (2) damage and pollination responses to manipulation of plant size and flowering traits in the year of treatment, and (3) plant-mediated indirect interactions between herbivores and pollinators. We found that plant traits had little effect on damage and pollination, but damage and pollination affected plant traits in both the treatment year and the subsequent year. We found evidence of indirect effects between leaf herbivores and pollinators in both directions; indirect effects of pollinators on leaf herbivores have not been previously demonstrated. Our results indicate that pollen receipt results in shorter plants with fewer stems but does not change flower number, while leaf herbivory results in taller plants with fewer flowers. Together, herbivory and pollination may contribute to intermediate plant height and plants with fewer stems and flowers in our system.     

Selection by Pollinators on Floral Traits in Generalized Trollius ranunculoides (Ranunculaceae) along Altitudinal Gradients

Abundance and visitation of pollinator assemblages tend to decrease with altitude, leading to an increase in pollen limitation. Thus increased competition for pollinators may generate stronger selection on attractive traits of flowers at high elevations and cause floral adaptive evolution. Few studies have related geographically variable selection from pollinators and intraspecific floral differentiation. We investigated the variation of Trollius ranunculoides flowers and its pollinators along an altitudinal gradient on the eastern Qinghai-Tibet Plateau, and measured phenotypic selection by pollinators on floral traits across populations. The results showed significant decline of visitation rate of bees along altitudinal gradients, while flies was unchanged. When fitness is estimated by the visitation rate rather than the seed number per plant, phenotypic selection on the sepal length and width shows a significant correlation between the selection strength and the altitude, with stronger selection at higher altitudes. However, significant decreases in the sepal length and width of T. ranunculoides along the altitudinal gradient did not correspond to stronger selection of pollinators. In contrast to the pollinator visitation, mean annual precipitation negatively affected the sepal length and width, and contributed more to geographical variation in measured floral traits than the visitation rate of pollinators. Therefore, the sepal size may have been influenced by conflicting selection pressures from biotic and abiotic selective agents. This study supports the hypothesis that lower pollinator availability at high altitude can intensify selection on flower attractive traits, but abiotic selection is preventing a response to selection from pollinators.     

Strong pollinator‐mediated selection for increased flower brightness and contrast in a deceptive orchid

Contrasting flower color patterns that putatively attract or direct pollinators toward a reward are common among angiosperms. In the deceptive orchid Anacamptis morio, the lower petal, which makes up most of the floral display, has a light central patch with dark markings. Within populations, there is pronounced variation in petal brightness, patch size, amount of dark markings, and contrast between patch and petal margin. We tested whether pollinators mediate selection on these color traits and on morphology (plant height, number of flowers, corolla size, spur length), and whether selection is consistent with facilitated or negative frequency‐dependent pollination. Pollinators mediated strong selection for increased petal brightness (Δβ_poll = 0.42) and contrast (Δβ_poll = 0.51). Pollinators also tended to mediate stabilizing selection on brightness (Δγ_poll = –0.27, n.s.) favoring the most common phenotype in the population. Selection for reduced petal brightness among hand‐pollinated plants indicated a fitness cost associated with brightness. The results demonstrate that flower color traits influence pollination success and seed production in A. morio, indicating that they affect attractiveness to pollinators, efficiency of pollen transfer, or both. The documented selection is consistent with facilitated pollination and selection for color convergence toward cooccurring rewarding species.     

蝶形花植物猪屎豆自花传粉机制研究

猪屎豆( Crotalaria pallida)为典型的蝶形花植物,分布极广,是路边或遭破坏生境中最常见的先锋种之一,野外观察未发现其有营养生殖的现象,主要为种子繁殖。该研究通过对自然生境中猪屎豆开花物候、访花昆虫及繁育系统的研究,旨在从繁殖的角度阐述其快速扩张的能力。结果表明：尽管猪屎豆的主要访花昆虫是蜜蜂,但蜜蜂的访花频率极低[(1.73±1.30)次/花序·h-1],且在整个花期内花药和柱头均被龙骨瓣包裹,蜜蜂访花时未成功接触柱头和花粉,不能实现传粉,因此蜜蜂不是猪屎豆有效的传粉昆虫,这与假说“蝶形花普遍是对膜翅目昆虫,尤其是对蜜蜂传粉的适应”不一致。人工授粉结果显示,猪屎豆为自交亲和种,不存在无融合生殖现象,其繁殖主要通过主动自交生产种子来实现,且在自交过程中长短花药都参与主动自交。这种自交方式不同于其他蝶形花植物的主动自交仅由短花药实现。对猪屎豆而言,长短花药均参与自交能够增加柱头的授粉几率,保证其在不利的生境中成功结籽,是其成功扩张的关键因素之一。     

Functional decoupling between flowers and leaves in the Ameroglossum pernambucense complex can facilitate local adaptation across a pollinator and climatic heterogeneous landscape

Decoupling between floral and leaf traits is expected in plants with specialized pollination systems to assure a precise flower–pollinator fit, irrespective of leaf variation associated with environmental heterogeneity (functional modularity). Nonetheless, developmental interactions among floral traits also decouple flowers from leaves regardless of selection pressures (developmental modularity). We tested functional modularity in the hummingbird‐pollinated flowers of the Ameroglossum pernambucense complex while controlling for developmental modularity. Using two functional traits responsible for flower–pollinator fit [floral tube length (TL) and anther–nectary distance (AN)], one floral trait not linked to pollination [sepal length (SL), control for developmental modularity] and one leaf trait [leaf length (LL)], we found evidence of flower functional modularity. Covariation between TL and AN was ca. two‐fold higher than the covariation of either of these traits with sepal and leaf lengths, and variations in TL and AN, important for a precise flower–pollinator fit, were smaller than SL and LL variations. Furthermore, we show that previously reported among‐population variation of flowers associated with local pollinator phenotypes was independent from SL and LL variations. These results suggest that TL and AN are functionally linked to fit pollinators and sufficiently decoupled from developmentally related floral traits (SL) and vegetative traits (LL). These results support previous evidences of population differentiation due to local adaptation in the A. pernambucense complex and shed light on the role of flower–leaf decoupling for local adaptation in species distributed across biotic and abiotic heterogeneous landscapes.     

Moth pollination of woody species in the Cerrados of Central Brazil: a case of so much owed to so few?

We present a survey of moth pollination in woody species of the Cerrado of Central Brazil. Although with the exception of Roupala montana (which has simple polysepalous flowers arranged in dense cymes) all moth pollinated species in this community have tubular flowers, or a pseudo-tube formed from a single folded petal in Qualea grandiflora, settling moth flowers (tube less than 15 mm) vs. hawkmoth flowers (tube more than 50 mm) are markedly different in size. Moths visit some 20 woody Cerrado species, but they are probably effective pollinators of only 13 species or ca.14% of the woody taxa studied, and even in these latter species they are often very sparse visitors. Nevertheless, it is notable that moths are pollinators for 21% of the 38 most commonly distributed woody Cerrado species. Moreover, the reproductive efficacy of the studied moth pollinated species was similar to that of species pollinated by other kind of vectors.     

ANTHER SMUT DISEASE IN DIANTHUS SILVESTER (CARYOPHYLLACEAE): NATURAL SELECTION ON FLORAL TRAITS

Mating opportunities, pollination intensity, and pollen dispersal ability may vary with variation in floral traits such as color, size, and shape. Where these traits are selected by pollinators for enhanced elaboration, they should evolve toward the equilibrium between selection for further elaboration and selection against this through reduced fecundity or vitality. Here we show that pollinator-borne fungal diseases of plants may be a factor influencing the position of this equilibrium. Populations of the rock pink, Dianthus silvester often contain individuals infected with the anther smut fungus Microbotryum violaceum (= Ustilago violacea). In a naturally infected population in the Alps of eastern Switzerland we investigated how intrapopulation variation in flower size and nectar rewards influenced spore deposition and how floral traits varied with disease status. We found that spore deposition increased with increasing petal size, suggesting that large-flowered plants were at a greater risk of disease. Spore deposition was also higher for plants growing in patches with many or a high proportion of diseased neighbors. Multiple regression analyses showed that petal size or nectar reward influenced spore deposition when the effects of neighborhood disease abundance were controlled statistically. In sequential analyses, after removing the effects of disease density or frequency and plant gender, petal length explained significant variation in spore deposition. Diseased plants had reduced female reproductive organs, but calyx size was intermediate between that of healthy perfect and female flowers of this gynodioecious-gynomonoecious species, and diseased plants bore flowers with the largest petals. This may reflect a symptom of this disease or the cause, if larger-flowered plants are more likely to become infected. We conclude that investment to pollinator attraction may bring an enhanced risk of contracting this sterilizing pollinator-borne disease, so natural selection by the fungus M. violaceum acts to lower attractiveness to pollinators.     

Adaptive plasticity of floral display size in animal-pollinated plants

Plants need not participate passively in their own mating, despite their immobility and reliance on pollen vectors. Instead, plants may respond to their recent pollination experience by adjusting the number of flowers that they display simultaneously. Such responsiveness could arise from the dependence of floral display size on the longevity of individual flowers, which varies with pollination rate in many plant species. By hand-pollinating some inflorescences, but not others, we demonstrate plasticity in display size of the orchid Satyrium longicauda. Pollination induced flower wilting, but did not affect the opening of new flowers, so that within a few days pollinated inflorescences displayed fewer flowers than unpollinated inflorescences. During subsequent exposure to intensive natural pollination, pollen removal and receipt increased proportionally with increasing display size, whereas pollen-removal failure and self-pollination accelerated. Such benefit-cost relations allow plants that adjust display size in response to the prevailing pollination rate to increase their attractiveness when pollinators are rare (large displays), or to limit mating costs when pollinators are abundant (small displays). Seen from this perspective, pollination-induced flower wilting serves the entire plant by allowing it to display the number of flowers that is appropriate for the current pollination environment.     

Optimal pollinator attraction strategies in Trollius ranunculoides Hemsl. (Ranunculaceae) at different altitudes: increased floral display or promotion of nectar output?

For alpine plant species, patterns of resource allocation to functional floral traits for pollinator attraction can be highly significant in adaptation to low pollinator abundance and consequent pollen limitation. Increased pollination can be achieved either through a larger floral display or production of more pollen rewards. In this study, variation in resource allocation to different components for pollinator attraction was studied along an altitudinal gradient in Trollius ranunculoides, an obligate self‐incompatible out‐crosser of the Qinghai–Tibet Plateau. We compared resource allocation to conspicuous yellow sepals (which mainly provide visual attraction) and degenerate petals (which provide the major nectar reward) between populations at four altitudes. Furthermore, we investigated the contribution of sepals and petals to pollinator attraction and female reproductive success in an experiment with sepal or petal removal at sites at different altitudes. At the level of single flowers, resource allocation increased to sepals but decreased to petals with increasing altitude. Consistent with these results, sepals contributed much more to visitation rate and seed set than petals, as confirmed in the sepal or petal removal experiment. Sepals and petals contributed to female reproductive success by ensuring visitation rate rather than visitation duration. To alleviate increasing pollen limitation with increasing altitude, resource allocation patterns of T. ranunculoides altered to favour development of sepals rather than petals. This strategy may improve pollination and reproductive success through visual attraction (sepal) rather than nectar reward (petal) over a gradient of decreasing pollinator abundance.     

“金虎尾路线”植物的花进化与传粉转变

以金虎尾科植物地理分布格局及迁移历史总结出来的“金虎尾路线”, 是解释热带植物洲际间断分布与长距离扩散格局的重要模式。金虎尾路线阐明了金虎尾科植物历史时期7次独立的从起源中心(南美洲)向旧世界(非洲和亚洲)的洲际长距离扩散事件。本文总结了金虎尾路线植物起源地与扩散地主要类群的花部特征与传粉系统, 以探讨这些类群及类似植物长距离扩散后的花进化与传粉转变等适应规律。金虎尾科的南美洲类群都有分泌油脂的萼片腺体, 花的形态结构非常保守, 是与美洲当地特有的条蜂科集油蜂长期协同进化的结果。金虎尾科的非洲类群花保守性消失, 花白色、辐射对称且无萼片腺体, 繁育系统为雄花-两性花异株(功能性的雌雄异株), 传粉者是采集花粉的蜜蜂科昆虫。亚洲的一些属发生了类似非洲类群的泛化适应转变, 但风筝果属(Hiptage)出现了镜像花、异型雄蕊和极度反折的花瓣, 且传粉者是亚洲特有的大蜜蜂(Apis dorsata), 显示出了非常特化的适应性转变。风筝果属所在支系的现存类群涵盖了南美洲、中美洲、非洲和亚洲等地的地方特有属, 体现了金虎尾路线整个迁移历史过程, 是认识金虎尾路线及其进化适应规律的关键类群, 值得在今后的研究中加以重视。     

Chrysophyllum marginatum (Sapotaceae): Generalist pollination and cryptic gynomonoecious

Chrysophyllum (Chrysophylloideae, Chrysophylleae) is the second largest genus in the Sapotaceae. Studies of pollination ecology in this genus are non-existent, although there are records of entomophily for this family. Considering the lack of detailed studies on pollination ecology and sexual systems in Chrysophyllum species, we investigate the floral morphology and biology and floral visitors of Chrysophyllum marginatum to verify which sexual system is present in the studied population and whether flowers of this species are visited and pollinated by different insect groups. The population of C. marginatum has weak and cryptic gynomonoecy because the plants produce a low percentage of functionally pistillate flowers (4.2%) and these flowers appear to be perfect flowers (hermaphrode). Flowers of C. marginatum are phenotypically, ecologically and functionally generalist because: (a) they are actinomorphic, open and not restrictive in terms of access to floral resources; (b) they are visited by 26 species of insects that are potential pollinators; and (c) among these species several groups can be effective pollinators, mainly bees and flies, according to the most effective pollinator principle. We consider bees and flies to be the main pollinator group of C. marginatum, due to their high visitation rate, richness and intrafloral visiting behavior, and because they especially forage among plant individuals and are able to promote xenogamy. Nectaries were found in the ovary base and osmophores in the petal margins, as floral attractants. For Chrysophyllum, this is the first record of gynomonoecy and for the family this is considered the second record. Chrysophyllum marginatum has generalist and entomophilous pollination, as recorded in other Sapotaceae Neotropical species.     

Floral morphological changes and reproductive success in deer weed (Lotus scoparius

Pollination-related and time-dependent floral morphological changes occur in a diverse set of angiosperm taxa and appear to be particularly common in species occupying resource-limited environments. In deer weed (Lotus scoparius), such floral modifications include a color change from yellow to orange and a folding of the banner petal down over the keel. These changes are rapidly induced by pollination, but will also occur much more slowly without pollination. Orange flowers typically lack nectar and pollen. We examined the reproductive success of these plants to test the hypothesis that retention of orange flowers increases pollinator visitation rate and fruit set while reducing costs to the pollinators. All of the common species of bee pollinators that visited deer weed easily distinguished between yellow and orange flowers at close range and preferentially probed yellow flowers. Retention of orange flowers by these plants resulted in a higher frequency of pollinator visits and a higher fruit set per flower than plants that lacked orange flowers. The number of flowers visited by each pollinator was lower on plants with a mixture of yellow and orange flowers, suggesting that the presence of orange flowers may reduce selfing. The possible selective pressures involved in the evolution of these mechanisms and their relation to stressful environments are also discussed.     

Reproductive success of Dactylorhiza incarnata ssp. incarnata (Orchidaceae): the effects of population size and plant visibility

Reproduction of plants pollinated solely by flower-visiting animals depends on the ability of the population and each of its flowering member to attract pollinators. Factors affecting the pollination of nectarless species differ somewhat from those affecting the pollination of rewarding species due to the avoidance behaviour of pollinators after visiting empty flowers.
We studied a non-mimic food-deceptive orchid, Dactylorhiza incarnata ssp. incarnata, in 16 populations in central Finland to examine if population properties and plant size affected reproductive success of plants.
We found that the number of flowering plants increased total pollinia removal and seed production of the population, but had no effect on reproduction of individual plants. Dactylorhiza incarnata occurred in open mires with virtually no rewarding species in the neighbourhood, but the distance from the forest edge did not have any effect on reproduction. However, increased variation in the number of flowers among within-population plants enhanced plant reproductive success. The increased variation probably hampered the learning process of flower visitors. Plant size affected reproductive success only in populations with a high general reproductive success indicating that in the rarely visited populations, pollination of individual plants is mainly affected by random effects.     

Pollination networks and functional specialization: a test using Lesser Antillean plant–hummingbird assemblages

Network analysis has in recent years improved our understanding of pollination systems. However, there is very little information about how functionally specialized plants and pollinators interact directly and indirectly in pollination networks. We have developed a parameter, Functional specialization index, to quantify functional specialization in pollination networks. Using this parameter, we examined whether different sized hummingbirds visit a distinct set of flowers in five hummingbird-pollinated plant assemblages from the Lesser Antilles, obtaining a simple relationship between hummingbird body size, network parameter and ecological function. In the Lesser Antilles, functionally specialized hummingbird pollination is distinct for plant species pollinated by the largest hummingbird species, whereas the pollination niche gradually integrates with the insect pollinator community as hummingbird body size decreases. The network approach applied in this study can be used to validate functional specialization and community-level interdependence between plants and pollinators, and it is therefore useful for evaluating and predicting plant resilience to pollinator loss, presently a global concern.     

Morphological variation in populations of Bletia purpurea (Orchidaceae) and description of the new species B. riparia

Bletia purpurea is the most widespread species in its genus. Morphological variation has been recognized throughout the range of its distribution. In this paper, the morphological variation from 63 populations (583 individuals) ofBletia purpurea is assessed to determine whether more than one species were present. Forty-four quantitative and qualitative characters were examined by univariate analyses and exploratory multivariate analyses. Univariate analyses indicate that quantitative characters such as lateral sepal width, petal. width, lip length, and lip width are significantly different for populations from Acazónica, Mexico. Floral parts in the populations from Acazónica are the smallest among all populations. Qualitative characters such as petals covering the lip midlobe and horizontal lip position are found exclusively in the same populations. We concluded that these populations should be described as a new species,B. riparia. Multivariate analyses indicated that morphological variation among the other populations cannot be ascribed to geographic distribution or ecological factors.     

DEVELOPMENT OF FLOWER FORM IN AN ALLOTETRAPLOID CLARKIA AND ITS PARENTAL DIPLOID SPECIES

The allotetraploid Clarkia delicata possesses a floral phenotype and breeding system intermediate to its diploid progenitors. Three patterns were observed in a comparative study of anther, sepal, and petal development using allometry and scanning electron micrographs. In Pattern 1 (e.g., anther), all three species are similar at inception and in subsequent development. Anthers of the allotetraploid mature at a size intermediate to both diploids. In Pattern 2 (e.g., sepal and petal limb), diploids exhibit divergent developmental patterns, and the allotetraploid develops similarly to one diploid. In Pattern 3 (e.g., petal size and shape), diploids exhibit divergent developmental patterns, and the allotetraploid is variously intermediate to both. In petal size (length vs. width), the diploid developmental pathways are parallel, and the allotetraploid is intermediate at all points of development. In petal shape (limb length above widest point/length below widest point vs. petal width), diploid developmental pathways intersect, and the allotetraploid is similar to one diploid at inception and the other in subsequent development.     

The allometry of fluctuating asymmetry in southern African plants: flowers and leaves

Several studies of fluctuating asymmetry (FA) in animals show that secondary sexual characters used in signalling have a negative relationship between size and asymmetry. Larger sexual traits are presumably more costly to produce, which should lead to greater developmental stress and corresponding increases in asymmetry. In the absence of among individual variation in the ability to handle these costs, the relationship between size and asymmetry should thus be positive. A negative relationship therefore suggests that expression of these traits is condition-dependent. In plants, flowers act as signals for pollinators and may show similar trends to animal signals. Leaves which are uninvolved in signalling should not. Moller & Eriksson (1994) found that 89% of species ( n = 16 of 18) with insect-pollinated flowers showed a negative relationship between petal size and asymmetry, while 79% of species ( n = 15 of 19) showed a positive relationship between leaf size and asymmetry. I carried out a similar study of 18 plant species. The average relationship between petal size and asymmetry did not differ significantly from zero in those species showing measurable FA in flowers ( n = 12). The relationship was significantly negative in one species, and significandy positive in another. On average, leaves in species with FA did not show a significant positive relationship between size and asymmetry ( n = 7). There was no significant difference in the slopes of the relationship between size and asymmetry for leaves and flowers. Levels of floral asymmetry for species with FA were significandy repeatable on individual plants in 33% ( n = 4 of 12) of species, but leaf asymmetry was not significantly repeatable in any species. It is argued that condition-dependence of traits need not result in a negative relationship between size and asymmetry.     

Distribution and abundance of butterflies in a mountain area in the northern Iberian peninsula

The effect of alutudinal range, distance to the latitudinal boundary of geographical range, body size and larval food plant on both the distribution and abundance of butterflies have been studied in a mountain area along a marked altitudinal gradient Multiple regression analysis revealed that distribution was positively related to altitudinal range and abundance Altitudinal range accounted for a great part of vanance in species distribution Altitudinal range increased as both distance to latitudinal boundary of geographical range and body size increased Abundance was not affected by altitudinal range, body size or distance to latitudinal boundary Larval food plants family was related to the abundance of butterflies, but not to distribution or altitudinal range These results suggest that regional distributions of butterflies are likely to be limited by climatic tolerances of species, while local abundance might be influenced by local resource levels