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Our objective was to determine whether changes in populations of forest-interior bird species were related to changes in extent of interior forest along Breeding Bird Survey (BBS) census routes in Massachusetts. We first identified a suite of 28 forest-interior bird species (FIA species), based on correlations between bird abundance (in 2003–2007) and extent of interior forest (in 2005) along BBS routes. From this group, we eliminated 13 species whose breeding habitats were described in the literature as including forest edge or second growth, resulting in a more stringently defined subset of 15 (FIB) species. We quantified the extent of forest and interior forest (>100 m from a forest edge) along BBS routes based on digitized aerial photographs from 1971, 1985, and 1999. We also quantified changes in abundance of the 28 forest bird species along BBS survey routes over the same time period. Overall, changes in abundance of FIB species paralleled changes in extent of interior forest, with 13 of 15 species showing positive correlations, 5 of which were significant. However, substantial variation occurred among species, including conspicuous declines in Hylocichla mustelina (Wood Thrush) and Piranga olivacea (Scarlet Tanager) and conspicuous increases in Vireo solitarius (Blue-headed Vireo) and Setophaga coronata (Yellow-rumped Warbler). Changes were not significantly related to either migratory status (Neotropical vs. other) or nest location (ground vs. arboreal). Several differences could be attributed to species-specific factors, such as reintroductions of Meleagris gallopavo (Wild Turkey) and Corvus corax (Common Raven) or introduction of competitors, such as Haemorhous mexicanus (House Finch) impacting Haemorhous purpureus (Purple Finch). Changes in some bird populations seem to reflect forest succession, e.g., Hylatomus pileatus (Pileated Woodpecker), while others are unexplained and may be due to changes on migratory routes or wintering grounds. Overall, loss of interior forest is an important incremental factor in forest bird population declines, although other factors had a greater impact in the period under study.

Flowering times are sensitive indicators of climate change and provide insight into the potential effects of such change on biological phenomena. The goals of this study were to evaluate the extent and patterns of changes in flowering times in a largely rural area of Massachusetts. We also wished to evaluate the relationship between the observed changes in blooming time and each species' average flowering date and status as native or nonnative. By examining correlations between patterns in our study and those in another Massachusetts study employing similar methodology, we evaluated the role of sampling error in reported interspecific differences. We compared flowering times since 2010 of 450 species, based on over 7,300 field observations, with historical flowering times through 1980, based on over 4,300 herbarium specimens. Gridded PRISM temperature data for Franklin County reveal increasing average annual temperature over the past 121 years, with an acceleration in the past four decades. Among plant species with five or more records in each time period, flowering times advanced an average of 4.5 days. Flowering of species blooming before the summer solstice advanced an average of 6.2 days, whereas taxa flowering after August advanced only 2.1 days. A regression of change in flowering time on mean flowering date for spring-blooming species predicts that a species blooming in early spring (mean flowering date of May 1) advanced 12 days between 1929 and 2013. The average change in flowering time did not differ between native and nonnative species and was unrelated to duration of the blooming period. Changes in flowering date of 221 taxa in Franklin County were positively correlated with changes in flowering date measured using similar techniques in neighboring Worcester County. The strength of these correlations was, however, strongly dependent on the sizes of the samples of records on which average flowering times were calculated. Thus, interspecific differences are subject to considerable sampling error and have little validity unless based on sufficient sample sizes, preferably 20 or more observations in each time period.

The consequences of initial variability in reproductive effort on later pollination and fruit development have frequently been investigated with flower removal experiments. Often, plants produce many fewer fruits than flowers, so flower removal might not be expected to alter subsequent growth or development patterns all that much. Yet, many studies have demonstrated such changes even for species with low average fruit set, which begs for an explanation. Many (at least seven, by our count) such explanations have been reported in the literature, but experimental support for most is limited. In summer 2014, we conducted a field experiment on a lowbush blueberry (Vaccinium angustifolium) farm in Maine. In this experiment, we coupled flower removal with three other treatments, each designed to assess the validity of one of three often-cited hypotheses invoked to explain why growth and development changes occur following flower removal: 1) “Short-term nutrient shortages;” 2) “spatiotemporal limitations;” and 3) “the compound interest effect.” The three respective treatments—foliar nitrogen fertilization, positionally biased flower removal, and defoliation—were designed to either intensify or weaken the apparent effects of flower removal if the corresponding hypothesis had merit. As in a 2013 preliminary experiment, flower removal elicited several statistically significant growth and development changes in blueberry, including increases in final leaf area, ripe fruit weight, fruit ripening rate, and relative fruit production. The additional treatments also elicited several significant plant responses, though not always with concomitant flower removal effects as well. For example, fertilization generally increased fruit cluster mass by harvest, but flower removal itself had no such effect on cluster mass. Most observed interactive effects between flower removal and the additional treatments either ran counter to expectations, were limited in scope, or couldn't be unambiguously interpreted. For at least a few observed changes, none of the additional treatments significantly altered the effects of flower removal. We conclude that current hypotheses for the mechanistic basis for changes induced by flower removal are inadequate, at least for blueberry, a species with frequently low fruit set even when managed commercially. However, strong intellectual and economic imperatives exist to encourage further investigation into this open question.Plants grown in horticulture or occurring as adventives outside their native range can provide insight into species’ fundamental niche requirements that might not be evident from the native range, or realized niche, alone. Such occurrences can also identify conditions that support individual survival, but do not currently sustain positive population growth (i.e., a species’ ‘tolerance niche’). Further, in the context of rapid climate change, horticultural and adventive occurrences beyond current range edges might circumvent natural dispersal limitations and facilitate species range shifts. To explore these concepts in the field, we investigated the history and structure of five newly discovered populations of naturalized Magnolia tripetala near horticultural sites in western Massachusetts, USA. This tree species is native to the southeastern US, but has been grown horticulturally in the Northeast since the 1800s. However, naturalized populations had not been well documented in the region previously, raising the possibility that the species’ escape has been triggered by recent climate change. With tree coring and life stage surveys, we asked whether the naturalized populations exhibited synchronous patterns of establishment and expansion, suggestive of climatic release and a shift from tolerance niche to fundamental niche conditions in the region. Across the five sites, we documented 660 individuals, with populations ranging in size from 46 to 396 individuals, including seedlings, saplings, and reproduct

Premise of research. Flowering times are sensitive indicators of climate change. This study explores important methodological issues in the use of samples of phenological records, quantifies change in flowering times, and examines causes of variability among species.Methodology. I used Monte Carlo simulations to explore effects of sample size on estimates of phenological statistics. I documented 60 yr of change in temperature and flowering times of forbs in Worcester County, Massachusetts, a largely nonurban area, using a combination of herbarium specimens and observations, and I tested several hypotheses using these data. I also compared changes in flowering times in eastern North America from several published studies.Pivotal results. Average spring temperatures increased 1.4°C (0.24°C/decade) during the last 60 yr. Mean and median flowering dates were most robust for small sample sizes, while early and late flowering dates and ranges were least stable. Mean flowering time advanced 2.9 d (0.4°C/decade),...

Nonnative species are a major component of global change and have been linked to ecosystem disruption, reduction of native species richness, and substantial economic costs. An understanding of the patterns of occurrence of nonnative species and the environmental correlates of their abundance is necessary to formulate an informed response to the threats posed by these species. While considerable work has been conducted in Europe on the overall patterns and changes in nonnative species, few comprehensive studies are available for other areas. Because patterns of nonnative success can be region-specific, the availability of data from multiple geographic areas is important. Here we use two floristic surveys conducted in the 1930s–1950s and 1980s–2000s, respectively, as a basis for describing patterns and changes in the nonnative vascular flora of Worcester County, Massachusetts. Established, nonnative species comprised 21%–36% of all species in the county's 60 towns. Nonnative species richness was mo...

The selective advantage of gynomonoecy, the sexual system wherein plants produce a mixture of female and bisexual flowers, is poorly understood. One hypothesis for the evolution of this system is that the absence of androecia from female flowers reduces herbivore damage to the gynoecia of these flowers. Here, we examined patterns of herbivore damage in 53 collections representing 25 species of asters and goldenrods from Massachusetts, USA. In these taxa flowers are crowded into compact capitula, with bisexual flowers occupying the centre and female flowers situated on the periphery. Damage to gynoecia of bisexual flowers was significantly greater than damage to gynoecia of female flowers overall, and in about half of the individual populations. We also compared damage to central and peripheral flowers in the heads of 16 collections of other Asteraceae that produce only bisexual flowers to see whether the location of flowers rather than their sex might determine the patterns of herbivory. In only one of these 16 collections did we find a significant difference in herbivory between flower positions. We conclude that herbivore damage is influenced by flower type in asters and goldenrods, a pattern consistent with a role for herbivory in the evolution and maintenance of gynomonoecy. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101, 544–552.

This paper summarizes a broad range of studies that have examined influences of recent climate change on plant phenology or distribution. Spring events such as leafing and flowering have typically advanced, some by several weeks, with median advances of 4–5 d per degree Celsius. Autumn events, such as leaf coloring or leaf fall, have usually become delayed, though with more variability than spring events. Changes in summer events have been mixed. Phenological changes have varied geographically, as have recent temperature changes. Most studies of at least several decades duration show the initiation of rapid changes in the 1970s or 1980s, paralleling patterns of temperature change. Plants and animals in a given area have often responded at different rates to temperature change, which is likely to change patterns of interaction between plants and their pollinators and herbivores. Altitudinal changes in plant distributions have been demonstrated in several areas, especially in Scandinavia and in Med...

Sedges of the genus Carex L. are mostly wind-pollinated, self-compatible, monoecious herbs in which female flowers are receptive before pollen is released (protogyny). One hypothesis was examined for the adaptive importance of the monoecious sexual system, namely that having two flower types permits flexibility in allocation of resources to male and female reproductive functions in the face of changing environmental conditions. Fourteen greenhouse experiments were conducted on a total of six Carex species in which I manipulated one or more of three environmental variables: nutrients, water, and light. These variables had small effects on the proportion of female flowers, though the effects were significant for at least one variable in 8 of the 14 experiments. High nutrient and light levels were generally associated with increased femaleness, while high water levels were associated with increased maleness. Increased female allocation in response to enhanced resource availability has been demonstrated in many species and is thought to reflect the greater potential fitness gains via the female function than via the male function when resources are plentiful. The opposite effects of water are anomalous and contrary to results in the literature. Because the effects of environmental manipulations on sex allocation are modest, the evolution and maintenance of monoecy in sedges probably reflect advantages other than flexible sex expression, at least in part. Selection for avoidance of self-pollination may have been particularly important in favoring the combination of protogyny and monoecy in Carex.

We investigated current forest composition in relation to land use history at Broad Meadow Brook, a 157 ha urban wildlife sanctuary in Worcester, central Massachusetts. We obtained historical information from aerial photographs dating back to 1938, maps dating to 1831, various published sources, and interviews with long-term residents. We sampled tree vegetation in 35 20 m × 20 m plots and understory vegetation in 140 5 m × 5 m subplots. We obtained ages of several dozen trees by coring. Most of the sanctuary supported dry, mixed-oak forest that has been subject to frequent fires. Disturbed oak woods bore a greater variety of plants than older oak forest, including several non-native species. Mesic forest supported Fraxinus americana, Acer rubrum, and A. saccharum, with an abundant A. platanoides understory, a legacy of nearby residential plantings. Acer rubrum heavily dominated wet woodland. A small, previously cultivated plot supported an open canopy of A. rubrum with a dense understory of herb...

We investigated the sexual system, floral biology, sporogenesis, and gametogenesis of Tetradium daniellii (Bennett) Hartley, which possessed distinct male and monoecious sexual phenotypes. Male individuals produced almost exclusively male flowers. In the years 2000–2002, the protandrous monoecious individuals had male and female flowering phases completely separated in time within and between the plants, while in 2003 and 2004, slight overlap of male and female functions occurred. During early floral development, all flowers were hermaphroditic. Dimorphic unisexual flowers resulted from later selective abortion of the gynoecium or androecium. Male flowers and their pollen in the two sexual morphs did not significantly differ in structure. Pollen grains from male flowers on both male and monoecious plants were fertile and could germinate on the stigmas of female flowers on monoecious plants. Maturation of female gametophytes in monoecious plants coincided with the release of the three‐celled pollen in the ...

Bertin, R. I., M. E. Manner, B. F. Larrow, T. W. Cantwell, and E. M. Berstene (Biology Department, College of the Holy Cross, Worcester, MA 01610). Norway maple (Acer platanoides) and other non-native trees in urban woodlands of central Massachusetts. J. Torrey Bot. Soc. 132: 225–235. 2005.—We investigated the contribution of non-native tree species to woodlands in and near Worcester, a city of 170,000 residents in central Massachusetts. We sampled species composition of canopy, sapling and seedling layers in 32 woodlands. At three additional sites, we collected additional information on Norway maple, including size/age data, abundance with respect to distance from woodland edge, and apparent mortality compared to that of other species. In all, we encountered 66 tree species, of which 28 were introduced. The most common non-native trees were Norway maple (Acer platanoides L.), black locust (Robinia pseudoacacia L.) and tree-of-heaven (Ailanthus altissima (Miller) Swingle). The last two are shade-...

Historically, dichogamy, the temporal separation of male and female function in flowering plants, has been interpreted as a mechanism for avoiding inbreeding. However, a comparative survey found that many dichogamous species are self‐incompatible (SI), indicating dichogamy evolved for other reasons. Here we reexamined the association between dichogamy and SI in a phylogenetic framework and tested the hypothesis that dichogamy evolved to reduce interference between male and female function. Using paired comparison and maximum likelihood correlation analyses, we found that protandry (male function first) is positively correlated with the presence of SI and protogyny (female function first) with self‐compatibility (SC). In addition, estimates of transition‐rate parameters indicated strong selection for the evolution of SC in protogynous taxa and a constraint against transitions from protandry to protogyny in SC taxa. We interpret these results as support for protandry evolving to reduce interference and prot...

Gynomonoecy is the sexual system in which individual plants bear both female and bisexual flowers. Little attention has been paid to the adaptive significance of this sexual system, which is particularly prevalent in the Asteraceae. We investigated one hypothesized advantage of having two flower types, namely that this arrangement permits flexibility in allocation of resources to male and female reproductive functions. We examined six species of goldenrod (Solidago), a genus of gynomonoecious, perennial herbs. In greenhouse experiments, we varied one or more of three environmental variables – light, nutrients and water – and/or examined heads in different positions on the plants. Most variables had little or no effect on the proportion of ray flowers. Significant effects were found for light in 0 of 5 experiments, for nutrients in 4 of 9 experiments and for water in 0 of 3 experiments. Heads in different positions in the inflorescence differed in the proportion of ray flowers in half of the experiments, though the differences were small. We also monitored temporal patterns in four species and found that the proportion of ray flowers increased significantly over the blooming period and the number of flowers per head declined. Because of the small number of significant effects and their modest magnitude, we conclude that the presence of two flower types in goldenrods is probably not advantageous in allowing flexibility in sex expression. It seems likely that this sexual system has been more important either in increasing pollinator attraction or in reducing pollen–pistil interference. The small observed changes in floral ratios were generally accompanied by changes in disc size in a manner consistent with an explanation based on allometry. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society, 2002, 77, 413–422.

Gynomonoecy is the sexual system in which female and bisexual flowers occur on the same plant. This system has received little attention despite the considerable work on other plant sexual systems in the past few decades. Our study examines one hypothesized advantage of having two flower types on a plant, namely that this arrangement permits flexibility in allocation of resources to male and female reproductive functions. We examined 16 species of Aster (Asteraceae), a genus of gynomonoecious, perennial herbs. Plants in this genus produce heads consisting of a whorl of female flowers around a cluster of bisexual flowers. Among field-grown plants we found no evidence that plant size, date, position of heads, rainfall, or shade influenced the proportion of female flowers. A series of greenhouse experiments likewise revealed no large or consistent effects of light, nutrients, or position of heads on the proportion of ray flowers. While floral ratios proved very stable in the face of environmental and physiological variables, they exhibited significant variation among plants and among sibships in most species. We conclude that the presence of two flower types in gynomonoecious asters is not advantageous in permitting flexibility in allocation of resources to male and female functions. We believe that the advantage of the female flowers in aster heads lies either in reducing pollen-pistil interference or in attracting pollinators.

Early flowering plants are thought to have been woody species restricted to warm habitats. This lineage has since radiated into almost every climate, with manifold growth forms. As angiosperms spread and climate changed, they evolved mechanisms to cope with episodic freezing. To explore the evolution of traits underpinning the ability to persist in freezing conditions, we assembled a large species-level database of growth habit (woody or herbaceous; 49,064 species), as well as leaf phenology (evergreen or deciduous), diameter of hydraulic conduits (that is, xylem vessels and tracheids) and climate occupancies (exposure to freezing). To model the evolution of species' traits and climate occupancies, we combined these data with an unparalleled dated molecular phylogeny (32,223 species) for land plants. Here we show that woody clades successfully moved into freezing-prone environments by either possessing transport networks of small safe conduits and/or shutting down hydraulic function by dropping leaves during freezing. Herbaceous species largely avoided freezing periods by senescing cheaply constructed aboveground tissue. Growth habit has long been considered labile, but we find that growth habit was less labile than climate occupancy. Additionally, freezing environments were largely filled by lineages that had already become herbs or, when remaining woody, already had small conduits (that is, the trait evolved before the climate occupancy). By contrast, most deciduous woody lineages had an evolutionary shift to seasonally shedding their leaves only after exposure to freezing (that is, the climate occupancy evolved before the trait). For angiosperms to inhabit novel cold environments they had to gain new structural and functional trait solutions; our results suggest that many of these solutions were probably acquired before their foray into the cold. © 2014 Macmillan Publishers Limited. All rights reserved.

The evolution of many floral traits, including monoecy and dichogamy, has been attributed to selection for avoidance of self-fertilization. If this explanation is correct, monoecy and dichogamy should be uncommon among self-incompatible species because physiological barriers prevent self-fertilization in such species. In fact, self-fertility was independent of sexual system in a sample of 588 hermaphroditic and monoecious angiosperms. Overall, dichogamy was also equally common among self-incompatible and self-compatible species. When the different forms of dichogamy were analyzed separately, only intrafloral protogyny was associated with self-compatibility. This form of dichogamy is less common among angiosperms than intrafloral protandry, which is probably less effective at reducing self-fertilization. Thus, avoidance of self-fertilization has probably been less important in the evolution of monoecy and most forms of dichogamy than other factors, such as avoidance of pollen-pistil interference, and flexibility of resource allocation to male and female functions.

We obtained information on dichogamy and other aspects of the biology of over 4200 species of angiosperms from several hundred published and unpublished sources. We used this information to describe patterns of occurrence of dichogamy and to test specific hypotheses relating dichogamy to other characteristics of plants or their environments. Protandry was more common than protogyny at the intrafloral level, but the reverse was true at the interfloral level. Patterns of dichogamy varied significantly among major taxa, with protogyny more common among monocotyledons and primitive dicotyledons, and protandry expecially common in the Asteridae. Arctic species tended to be less dichogamous and more protogynous than temperate and tropical species. Aquatic and alpine species were especially protogynous. Patterns of dichogamy varied among sexual systems, with gynomonoecious and gynodioecious species especially protandrous, and monoecious species highly protogynous. Autogamous and self-compatible species were disproportionately protogynous. Flowers of intraflorally dichogamous species were slightly larger than those of adichogamous species, owing to the presence of many autogamous species in the latter group. Species with interfloral protogyny bore much smaller flowers than did species with interfloral protandry. Early-blooming species in north-temperate and polar regions were disproportionately protogynous. Sexual structures that abscised, shriveled or moved after completion of their function tended to be presented first, and those that facilitated the other sexual function were presented second. A negative association existed between type of intrafloral and interfloral dichogamy in diclinous species. Most animal-pollinated flowers were protandrous, except beetle-pollinated and refuge and trap blossoms. Wind pollination was markedly associated with protogyny. Vertical inflorescences visited by upwardly-moving vectors were protandrous. Our results suggest that three primary factors may be involved in promoting dichogamy: selection for avoidance of pollen-pistil interference, selection for avoidance of self-fertilization, and selection for synchrony of pollen discharge and stigma receptivity in the different flower types of diclinous species. In contrast to many earlier workers we reject the thesis that avoidance of self-fertilization is the universal or even the most important force in the evolution of most forms of dichogamy. We attribute the prevalence of intrafloral protandry to selection for avoiding interference between pollen export and pollen receipt. Intrafloral protogyny was associated with imprecise pollen transfer, where other means of avoiding pollen-pistil interference (e.g., herkogamy) are likely to be of limited value. The prevalence of interfloral protogyny seems to reflect the smaller size of unisexual flowers than bisexual flowers, the absence of intrafloral pollen-pistil interference in diclinous species, and selection for synchrony of pollen discharge from one flower type with stigma receptivity in the other.

We investigated paternal effects on seedling performance in relation to patterns of fruit abortion in Campsis radicans using a series of 14 experiments with various combinations of pollen donors and recipients. In eight experiments significant paternal effects on three or four dependent performance variables were detected by multivariate ANCOVA. These effects were independent of seed weight, which was controlled in the experimental design and in the statistical analysis. In six of the eight experiments with significant results the favored pollen recipient sired the more vigorous offspring. In general, therefore, patterns of fruit abortion with respect to outcross donor enhance progeny fitness. Maternal discrimination is reduced, however, when pollen from several outcross donors is deposited on the same stigma, a likely occurrence in nature. Discriminntion among pollen from different outcross donors is also less important than the ability to discriminate between self- and cross-pollen because the latter di...

I examined effects of pollination intensity on fruit, seed and seedling characteristics in Campsis radicans, and joint effects of pollen donor and pollination intensity on fruit production. Large pollen loads were more likely to initiate fruit production than small pollen loads, and the former fruits contained more seeds and a greater total seed mass. No further increases in seed number or mass occurred for pollen loads above 4,000 grains. The weight of individual seeds was unaffected by pollen load. Effects of pollen donor were generally larger than effects of pollen load, and fruit production from small loads of pollen from one donor were sometimes equal to fruit production from larger pollen loads from another donor. The ratio of pollen grains deposited to resultant seeds increased with pollen load, and several explanations are proposed. Seeds from heavy pollinations emerged better than seeds from light pollinations, but did not differ in speed of germination or in the performance of seedlings up to 126 days. The emergence differences are probably due to differing intensities of pollen tube competition.

Nature 506, 89–92 (2014); doi:10.1038/nature12872 corrigendum Nature 514, 394 (2014); doi:10.1038/nature13842 Three readers pointed out that in this Letter we applied the threshold of 0.044 (the size at which freezing-induced embolisms are believed to become frequent at modest tensions) to the area of the conduit (in mm2) rather than the diameter (in mm).

In a recent review of self-incompatibility (SI) in flowering plants, Dickinson (1990) noted that ‘SI in angiosperms is probably the best defined cellular communication system in the plant kingdom. Its genetic basis is now well established, the cells involved are clearly identifiable, the time of interaction is known, and the consequences of the communication are easy to detect’. This statement may be true for the better known examples of SI in which multiple alleles of an incompatibility (S) gene control arrest of self-pollen tubes in the stigmatic or stylar regions. It is not true, however, for an increasing number of species that have been found to have ovarian or ovular arrest (Seavey and Bawa 1986). These systems of ovarian self-incompatibility (OSI) remain poorly defined but, nevertheless are likely to be evolutionarily important (Barrett 1988). The scarcity of attention given to the characterization of OSI systems has occurred in part because they were initially assumed to be uncommon (de Nettancourt 1977), a notion which Seavy and Bawa (1986) pointed out to be erroneous. Although OSI systems have been reported to occur primarily in woody species, incompatible pollen tube arrest within the ovary has now been reported for a number of herbaceous monocotyledonous and dicotyledonous species as well (Seavey and Bawa 1986). Kenrick et al. (1986) noted that the rarity of ovarian incompatibility may have been exaggerated by the preference of investigators for small, short-lived, herbaceous plants for studies of breeding systems.

We examined spatial and temporal patterns of pollen receipt, pollen removal and maternal reproductive success in Geranium maculatum. These three variables differed among sites and sampling dates. Sites with the densest tree canopy had the lowest pollen receipt and fruit production. Differences between years were accompanied by different climatic conditions and may have been caused by different levels of pollinator activity. Within blooming seasons, fruit production and pollen receipt declined at all sites with date, accompanying canopy closure. Pollen removal varied with date, but not in parallel with pollen receipt, indicating that pollen receipt and deposition were influenced, in part, by different factors. Of three weather variables examined, ambient temperature was significantly positively correlated with rate of floral development, but not consistently with pollen receipt, pollen removal or fruit production. Pollen receipt was inversely related to cloud cover, presumably due to effects of the latter on pollinator activity. The earliest-blooming plants had the highest reproductive success.

I examined the relative success of pollen donors in siring viable seeds following mixed (two-donor) hand pollinations of the woody climber, Campsis radicans. Paternity was assigned using an electrophoretic marker. When pollen from two donor plants was mixed and applied to stigmas, the numbers of viable seeds sired by the two donors were generally unequal. The relative success of the two donors in a mixture was correlated with the relative success of the two donors when their pollen was applied in single-donor loads to different stigmas on the same plant. However, performances of two donors were generally more equal when their pollen was applied in mixed loads than when applied in singledonor loads. While single-donor pollinations are often used to assess donor performance in studies of plant paternity, the above results suggest caution in extrapolating from success in single-donor pollinations to success in nature, where mixed pollinations are probably the rule. When ratios of pollen from two donors in a mixture changed, the success of the two donors changed roughly in proportion. Thus there is no basis for challenging the frequent assumption in gender allocation models that changes in pollen production produce proportional changes in male success. Relative performance of pollens in a mixture was unaffected by the total number of pollen grains deposited. Several lines of evidence suggest that postzygotic phenomena (e.g., seed abortion) are important in determining the success of different pollen donors in Campsis.

Seed biomass, seed number and biomass of "packaging" (dispersal and protective devices associated with those seeds) were determined for 28 species of flowering plants. Individual variation in average seed packaging investment was marked in almost all species we surveyed. Furthermore, the pattern of biomass investment in dispersal devices and protective enclosures relative to associated seed biomass or seed number commonly differed among conspecific maternal parents: some individual parents invested more in dispersal and protection when associated seed biomasses or numbers were large, and others did not. Despite the variable relationships between seed biomass and packaging biomass within seed crops, individuals of most species varied sufficiently that significant positive correlations were found when all conspecifics were pooled. The widespread existence of such variation indicates a considerable potential for selection on seed packaging.

The Ruby-throated Hummingbird (or rubythroat, Archilochus colubris) and several of its major food plants were examined to assess the importance of rubythroat versus insect pollination, the overlap of geographical ranges, and the synchrony between migration and flowering times. Seed set of Impatiens biflora was increased 8–17% by rubythroat and insect visitation over the level achieved by insects alone. The rubythroat's range is not contiguous with that of any of 22 putative food plants examined, but is nearly coincident with the range of certain forest types, perhaps reflecting the importance of sap for food. A new method was developed to estimate peak flowering times of plants from herbarium data. Based on these data and field observations, only one rubythroat food plant (Impatiens biflora) had peak flowering times close to peak rubythroat migration times throughout their shared range. Rubythroats and their North American food plants are facultative mutualists, with the plants apparently having been evolutionarily more labile.

The tendency in Campsis radicans for fruits to be produced from certain crosses was consistent between years. This increases the likelihood that observed patterns are genetically based. Early in a season, plants were more selective about which donor they accepted pollen from, as measured by the parentage of mature fruits. Field experiments indicated that this increase in selectivity was related not to date, but to the number of prior pollinations and developing fruits in an inflorescence, and therefore presumably to the availability of resources. These differences in fruiting indicate a non-male component to selectivity (since pollen source was controlled). That the acceptability of pollen from particular donors depends on the resource status of the inflorescence means that the distinction between pollen limitation and resource limitation of fruit production is not a sharp one. A model is proposed to account for patterns of fruit production with respect to paternity in Campsis radicans.

Campsis radicans is almost completely self-sterile following pollinations of pure self-pollen, but when self- and cross-pollen are present in similar amounts, ca. one in six viable seeds is sired by self-pollen. The amount of selfing depends in part on the identity of the cross-pollen donor in the pollen mixture. Selfed seeds are smaller on average than outcrossed seeds. Seed sizes in fruits from mixed (self + cross) pollinations are more variable than those from cross-pollinations, with a larger number of small, often inviable seeds. Most of these small seeds are presumed to be products of selfing. Selfed seeds do not occur in particular positions along the length of the fruit. After 6-7 wk seedling growth, outcrossed seedlings were taller and heavier than selfed seedlings. Selection for the avoidance of selfing is likely to have been important in the evolution of protandry in Campsis and perhaps in the large "overproduction" of flowers, which permits selective fruit abortion. We discuss the possible rol...

The effect of self pollen on the success of cross pollinations was studied in Campsis radicans (L.) Seem., a species previously considered self-sterile. The application of self pollen to stigmas in combination with or preceding the application of cross pollen markedly reduced the likelihood of fruit production. This effect was not due to the dilution of cross pollen nor to physical blocking of the stigmatic surface, since mixtures of talc and cross pollen were as effective as pure cross pollen in causing fruit production. Pollen tubes produced by self pollen grew at rates similar to those from cross pollen, and penetrated the ovary. The interference caused by self pollen appears to take place in the ovary, although it cannot be stated to what degree it is prezygotic or postzygotic. The marked protandry occurring in C. radicans is presumed to be due at least partly to selection for avoidance of these negative effects on female reproductive success. Up to 33% of viable seeds from mixed self + cross pollinations were sired by self pollen. The term "cryptic self-fertility" is coined to describe this phenomenon where pollination with loads of pure self pollen rarely or never yields fruit, but pollination using mixtures of self and cross pollen yields fruit containing considerable numbers of selfed seed. Estimates of selfing frequency that are based on pollination using loads of purely self pollen will be in error for species possessing cryptic self-fertility. SEVERAL REPRODUCTIVE traits of seed plants cause a separation of male and female sexual functions. Such traits include dichogamy, herkogamy, and breeding systems such as monoecy and dioecy. One possible advantage of such traits is that they reduce inbreeding, a reduction that would be favored in species wherein inbreeding depression yields offspring of low fitness. However, dichogamy, herkogamy and monoecy all occur in plant species having physiological self-incompatibility (Lloyd and Webb, 1986), indicating that prevention of inbreeding depression is not a complete explanation of these traits. An alternative explanation is that such traits are beneficial in reducing mutual interference of male and female reproductive functions, caused by self-pollination. Self-pollination could decrease female success even in a self' Received for publication 19 May 1987; revision accepted 4 November 1987. We thank C. Barnes, P. L. Angermeier, M. N. Melampy, and L. Wolfe for assistance with field work, and M. F. Willson for accommodations and lab space in Illinois. S. I. Guttman kindly allowed the use of his laboratory and provided advice concerning electrophoresis. G. J. Anderson, C. T. Philbrick and M. L. Ledbetter graciously allowed use of fluorescence microscopes and/or provided advice on the visualization of pollen tubes. S. C. H. Barrett, K. S. Bawa, R. N. Bowman, B. B. Casper, D. G. Lloyd and an anonymous reviewer kindly commented on earlier versions of this paper. This research was supported by the National Science Foundation (DEB 8206465) and by a Batchelor (Ford) summer fellowship to RIB. incompatible plant if self pollen on the stigma interferes with the deposition or performance of compatible pollen (discussion in Shore and Barrett, 1984). Self pollination would also decrease male success ofa self-incompatible plant because self-deposited pollen is unavailable for transport to other, compatible plants. The potential importance of selection for avoidance of pollen-stigma interference in the evolution of monoecy and dioecy has been noted by Bawa and Opler (1975), Zapata and Arroyo (1978), Bawa (1980) and Bawa and Beach (1981). Others, including Yeo (1975) and Lloyd and Yates (1982), have suggested that reduction of pollen-stigma interference could be important in the evolution of heterostyly. Most recently Lloyd and Webb (1986) and Webb and Lloyd (1 986) have argued for a central role of pollen-stigma interference in the evolution of dichogamy and herkogamy. Despite this growing theoretical literature, empirical studies of pollen-stigma interference are few. Crowe (1971) demonstrated interference of incompatible pollen with the performance of compatible pollen in Borago officinalis. Flowers receiving compatible pollen on one stigmatic lobe and incompatible on the other produced fewer than 5% as many seeds as flowers receiving compatible pollen on both lobes. In the distylous species Turnera ulmifolia, however, Shore and Barrett (1984) found a deleterious effect of self pollen on the performance of cross pollen only when a large (five

Trumpet creeper is self-incompatible and bears long, tubular, orange flowers from June to September. Flowering peaks rapidly, then declines and continues at low levels for several weeks. The initial burst of flowering may attract pollinators that return even during subsequent reduced flowering. Most flowers open before noon and nectar production totals 110 ,l of 26% sucrose equivalents per flower, an exceptionally high production for a temperate zone plant. Production ceases within 20-30 hr of flower opening, but corollas persist for several days and may serve to attract pollinators. Effective pollination reduces the period of stigma receptivity and speeds closing of stigma lobes. Only 1-9Wo of flowers produced mature fruits at four sites in Illinois and Missouri. Roughly 400 pollen grains had to be deposited on a receptive stigma to cause fruit development beyond an initial period of high abortion. At two sites, 17% and 89% of stigmas received over 400 pollen grains. Assuming 50% of deposited grains were from the same plant, fruit production at one site was clearly pollinator limited, that at the second site may have been. Ruby-throated Hummingbirds (Archilochus colubris) deposited ten times as much pollen per stigma per visit as honeybees (Apis mellifera) and bumblebees (Bombus spp.). Fruit set was highest where rubythroat visitation was most frequent. Trumpet creeper appears primarily adapted for hummingbird pollination, but can also be adequately pollinated by honeybees and bumblebees. This is one of the first attempts to relate pollen-depositing capabilities of pollinators of any plant to pollen requirements for fruit production. Several characteristics suggest that trumpet creeper may be adapted to pollination at low densities (often called traplining) in its presumed original, woodland, habitat.

To learn some of the bases for consumption of temperate fleshy fruits by birds, we examined nutritional and morphological traits of temperate fleshy fruits and made laboratory obser? vations on consumption of individual fruit species using 18 fruit species and 11 migrant frugivorous bird species in Illinois. The only seasonal trends in fruit traits were interspecific increases in absolute quantity of potassium and protein per fruit. Fruit energy content did not differ among species having bicolored vs. monochrome or small vs. large fruit displays. The fruit mass consumed was correlated best with dry pulp mass per fruit, providing significant positive correlations in 6 of 11 frugivorous species. Large fruit size relative to bill size did not appear to affect fruit consumption over the range of fruit sizes and bird species used. Because retained energy was correlated with mass consumed, the fruit pulp mass consumed was in most cases a good index of the energy obtained. Some significant differences occurred in digestive efficiency of a bird species eating different fruit species, and among different bird species eating a single fruit species, but no trends were apparent. Regurgitated seeds generally spent less time in a bird than did defecated seeds, facilitating more rapid disposal of seed ballast. Smaller birds defecated only small seeds and regurgitated some small seeds as well as all large ones, whereas larger birds defecated all smaller seeds and many larger ones. Consequently, resultant seed shadows may depend upon both bird and seed size.

We examined seed-mass variation in 39 species (46 populations) of plants in eastern-central Illinois, USA. The coefficient of variation of seed mass commonly exceeded 20%. Significant variation in mean seed mass occurred among conspecific plants in most species sampled (by hierarchical ANOVA), averaging 38% of total variance. For most species, within-plant variation was the larger component of total variance, averaging 62% of total variance. Variation in seed mass among fruits within crops was significant in most species tested. We conclude that variation in seed mass among and within plants is widespread and common. There was little evidence of trade-offs between number of seeds and mean or variance of seed mass, and little correlational evidence of local competition for maternal resources. No consistent ecological (dispersal mode and growth form) correlates of variance of seed mass were evident.

The effect of paternity on the likelihood of fruit production was determined by making 2,486 hand pollinations among 11 stems (9 individuals) of Campsis radicans. All individuals matured significantly different numbers of fruit from different pollen donors. Individuals that were favored as donors by one recipient were not necessarily those favored by other recipients. Selectivity increased slightly as more pollinations were made, and pollination by nonfavored donors was more successful in producing fruit during the first half of the pollination sequence than in the latter half. The pollen donors favored by particular recipients were usually those whose pollinations resulted in fruit with relatively many and large seeds. Fruit abortion seems to have been more important in donor selectivity than prezygotic phenomena, although parallels with multifactorial gametophytic incompatibility are evident. I suggest this selectivity by a pollen recipient with respect to pollen donors is an integrated response increas...

I examined the effects of pollen loads containing pollen from one, three and five donors on fruit production and fruit quality in Campsis radicans. Number of pollen donors had no significant effect on % fruit production, seed number, seed weight or seed germination. In singledonor pollinations the identity of the donor did have a strong effect on the above parameters. Furthermore, the best single donor sired fruits with more seeds and heavier seeds than any mixture containing this donor. This pattern indicates interference of pollens or preemption of some ovules by the inferior pollen. In Campsis, therefore, the number of pollen donors contributing to a pollen load is less important than the identity of these donors in determining fruit production and fruit quality. Seeds from fruits resulting from mixed pollination were slightly more variable than seeds from fruits resulting from single-donor pollinations.

We presented flesh flies (Sarcophaga bullata) with a choice between artificial nectar (10 % sucrose) and artificial nectar containing one of 20 amino acids. Flies tested immediately after eclosion did not consistently prefer either solution. Flies maintained on a sugar only diet for 8 days preferred the amino acid solution in six of 19 trials. This preference was particularly marked in the case of histidine. Flies maintained on a liver only 1iet suffered high mortality, but preferred the amino acid solution in four of 10 trials, and the sugar solution in one trial. Flies avoided solutions containing histidine and lysine, but preferred glycine, at concentrations much higher than those normally found in nectar. Thus flesh flies preferred solutions containing some amino acids at concentrations comparable to those occurring in floral nectar. We suggest that such preferences are likely to have selected for the high amino acid contents in the nectars of some fly-pollinated flowers, and form a basis for at least some correlations between pollination syndrome and amino acid levels in nectar.

scientific study. In very few cases, however, do we understand why a species occurs in a particular habitat, either in an ultimate (evolutionary) sense or a proximate (behavioral) sense. Before these questions can be adequately approached, a knowledge of the quantitative aspects of species' habitats is necessary. Most information on this subject comes from comparative habitat analyses (e.g., Sturman 1968, Wiens 1969, James 1971, Anderson and Shugart 1974). Vegetation structure has been emphasized heavily in such studies and often has been adequate to measure habitat differences among species. Floristic and physical factors have received less attention although MacArthur (1964) suggested that the latter may be important for at least some species. This study examines quantitatively the habitats of two woodland thrushes, the Wood Thrush (Hylocichla mustelina) and the Veety (Catharus fuscescens). My purposes were to determine how and to what extent their habitats differed and to indicate factors which seemed to be favored by each species in its selection of habitats. Some physical and floristic, as well as structural, habitat features were included to examine their effects on the

Asclepias verticillata is self-incompatible and can propagate vegetatively. Nectar is produced mainly between 1800 and 2200 hr, throughout the 4-5 day life of the flower. Insect visitations at this time were infrequent on all four study sites, a seemingly anomalous situation ; most pollinia vectors visited the flowers during the day. The most frequent vectors were Hymenoptera, especially wasps and honeybees, and Lepidoptera, especially moths and the introduced cabbage white butterfly. Most flower-visiting insects were nectar thieves, carrying no pollinia. None of the potential pollinators seem to be closely coevolved, morphologically or seasonally, with the flowering of A. verticillata. The probability of an individual flower being visited by a potential vector is very low, corresponding to the observed low percentage of pod set, but between-site differences in composition of the vector fauna (proportional similarities less than 36%) and rates of visitation were not correlated with differences in levels of fruit production. Our earlier studies of the floral display and fruit production of Asclepias (Willson and Rathcke, 1974; Willson and Price, 1977) showed that fruit set varied considerably within and between conspecific populations. Furthermore, casual observations indicated marked spatial variation in insect visitors to A. verticillata. Roadside populations could often be spotted at a distance by the clouds of pierid butterflies clustered over the flowers, whereas flowers in other areas were seldom visited by pierids. These observations suggested that different populations of A. verticillata might encounter such different pollinator faunas that differences in timing and success of fruit production might result. We examined both temporal and spatial variation of the insect visitors and potential pollinators of A. verticillata and monitored temporal patterns of nectar production. Specifically, we here address the following questions: (1) Which insect visitors carry pollinia and are potential pollinators, and which visit the flowers for nectar but do not carry pollinia, and hence function as thieves? (2) Does the rate of visitation, the composition of the fauna of potential pollinators, and the proportion of visits made by thieves vary between sites or seasonally? Can these factors be related to fruit production? (3) Can the temporal pattern of nectar production be related to daily patterns of flower visits by potential pollinators?