COMPETITION FOR POLLINATORS IN THE ECOLOGY OF <i>CENTAUREA SCABIOSA</i> L. AND <i>CENTAUREA NIGRA</i> L.

Lack, Andrew

doi:10.1111/j.1469-8137.1982.tb03316.x

Cited by 39 publications

(35 citation statements)

References 18 publications

(16 reference statements)

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“…In the autumn, it is possible that there are other selection pressures, such as parasites or frost, which act against late flowering, keeping the flowering time of C. nigra close to that of C. scabiosa. Therefore, despite the very slight difference in flowering time between the species on the Devil's Ditch, competition for pollinators (perhaps not solely between the species of Centaurea) may be one of the important selection pressures (see discussion in paper III, Lack, 1982b).…”

Section: Discussionmentioning

confidence: 99%

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COMPETITION FOR POLLINATORS IN THE ECOLOGY OF CENTAUREA SCABIOSA L. AND CENTAUREA NIGRA L.

Lack

1982

New Phytologist

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SUMMARYIf competition for pollinators is an important influence on populations of Centaurea scabiosa and C. nigra sensu lato one of the characters most likely to be affected is flowering time. Observations were made on the flowering period of several populations of the two species growing sympatrically and in isolation, and on plants from these and further populations transplanted into the Botanic Garden.Conclusions from the study are: (1) Where C. scabiosa and C. nigra grow sympatrically, C. nigra flowers slightly later than C scabiosa but there is a considerable period of overlap. The large range of flowering time seen in C. nigra may be partly attributable to differences between ssp. nigra and ssp. nemoralis and hybridization between them, but local ecological factors are important influences on some populations. Competition for pollinators between C scabiosa and C. nigra may maintain the difference in flowering time between the two species in some areas.

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Section: Discussionmentioning

confidence: 99%

“…Paper II (Lack, 1982 a) considers nectar production in the two species of Centaurea (the attractant and food for which nearly all the insect visitors to Centaurea forage) and paper III (Lack, 1982b) considers the numbers of insect visits that each species receives and the effect of this on the number of successful pollinations.…”

Section: Introductionmentioning

confidence: 99%

COMPETITION FOR POLLINATORS IN THE ECOLOGY OF CENTAUREA SCABIOSA L. AND CENTAUREA NIGRA L.

Lack

1982

New Phytologist

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“…If the number of visiting insects is low this may result in poor seed set by C. nigra owing to limited pollination. This idea will be discussed further in paper III (Lack, 1982b). Competition for pollinators between the two species does not appear to have affected nectar production in these species since there was no significant difference between any of the C nigra populations.…”

Section: Discussionmentioning

confidence: 97%

“…Capitula on yellowing shoots produced much less nectar than healthy ones, and at this season the average quantity of nectar produced per open capitulum may be lower than is suggested by my results. Senescence may have affected the number of insect visits to the species at the end of the season (see paper III, Lack, 1982b). The very large amount of nectar secreted by C. scabiosa in August 1977 may have been a consequence of the warm, dry summer of 1976 which possibly enabled C. scabiosa to store large reserves of energy (it did not suffer badly from the drought).…”

Section: Discussionmentioning

confidence: 99%

“…In general those plants (or capitula) which secreted a greater quantity of nectar retained a lower concentration (since evaporation would be relatively slower) and on warm, sunny days this effect was quite large (the mean of florets in one capitulum differing by up to 25% from another plant of the same species). Insects are sensitive to differences in concentration of nectar as well as quantity, and bees, the main pollinators of Centaurea (see paper III, Lack, 1982b), will visit flowers with nectar of less than 30 to 35 % sucrose equivalent less frequently than those with higher concentrations (Corbet, 1978, Corbet et al, 1979. Many Centaurea capitula had nectar with concentrations of less than 30% before 10.00 h, but after this the concentration was nearly always higher in both species, and it was only after about 10.00 h that the insects reached a peak of activity on the sites.…”

Section: Discussionmentioning

confidence: 99%

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COMPETITION FOR POLLINATORS IN THE ECOLOGY OF CENTAUREA SCABIOSA L. AND CENTAUREA NIGRA L.

Lack

1982

New Phytologist

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SUMMARYThe insects which visit Centaurea scabiosa and Centaurea nigra feed mainly on nectar and are likely to visit more frequently the species which produces most nectar. Nectar was extracted from plants in field populations and from plants transplanted into the Botanic Garden, to determine diurnal pattern and total quantity and concentration of nectar produced over 24 h periods.Florets of both species open in the morning and secrete nectar fairly constantly through the first day of floret opening. C. scabiosa florets continue to secrete into the second day when more florets start to open, hut C. nigra usually ceases to secrete nectar around 18.00 h on the first day. C. scabiosa at all times produced more nectar than C. nigra, and on average produced about four times as much. On Hod Hill plants of C. scabiosa produced slightly more nectar than those on the Devil's Ditch. There was no difference between different C. nigra populations. Different plants within each population differed considerably, one plant producing up to six times as much as another under fairly uniform conditions. Less nectar was secreted in cool weather or on a cloudy day than on a warm sunny day, and capitula on shaded shoots produced less than those in the sun. Capitula produced at the beginning and end of the flowering season appeared to secrete less than those produced in the middle. There was a large difference between years in some plants and plants studied in August 1977 produced more than those studied at any other time.

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Fitness benefits and costs of floral advertising traits: insights from rayed and rayless phenotypes ofAnacyclus(Asteraceae)

Cerca

Agudo

Castro

et al. 2019

American J of Botany

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PREMISE OF THE STUDY:Ray flowers commonly observed in daisies' flowering heads are a well-known example of advertising structures for enhancing pollinator attraction. Despite this, ray loss has occurred in multiple lineages, which still rely on pollinators, suggesting that rayless phenotypes could also be adaptive for animal-pollination. Here, we investigate the benefits and costs of these specialized floral advertising structures by comparing rayed and rayless phenotypes in two hybridizing closely related species. METHODS:We assessed the advantages and costs of ray production in terms of floral visitor's attraction, pollen limitation, and female reproductive success using the broad natural variation on ray size and number at the contact zone of A. clavatus (rayed) and A. valentinus (rayless). In addition, we experimentally explored the effect of rays under controlled neighborhoods and the effect of ray removal on fruit production. KEY RESULTS:In sympatry, rayed phenotypes attracted significantly more visitors than rayless plants, in which seed production was pollen limited. However, rayed phenotypes did not show higher fruit set or seed production than rayless phenotypes. Fruit set and seed production benefited from denser neighborhood displays and larger individual floral displays, respectively. The removal of ray florets did not appear to enable resource reallocation to fruit production. CONCLUSIONS: Rayless heads compensated their lower visitation rate by means of a higher number of flowers per head achieving similar fecundity levels to rayed plants. The larger size of rayless heads might thus indicate an inflorescence-level trade-off between attraction and fertility.

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COMPETITION FOR POLLINATORS IN THE ECOLOGY OF CENTAUREA SCABIOSA L. AND CENTAUREA NIGRA L.

Cited by 39 publications

References 18 publications

COMPETITION FOR POLLINATORS IN THE ECOLOGY OF CENTAUREA SCABIOSA L. AND CENTAUREA NIGRA L.

COMPETITION FOR POLLINATORS IN THE ECOLOGY OF CENTAUREA SCABIOSA L. AND CENTAUREA NIGRA L.

COMPETITION FOR POLLINATORS IN THE ECOLOGY OF CENTAUREA SCABIOSA L. AND CENTAUREA NIGRA L.

Fitness benefits and costs of floral advertising traits: insights from rayed and rayless phenotypes ofAnacyclus(Asteraceae)

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