Search Results - (Author, Cooperation:P. R. Grant)

2015-02-18

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

Animals ; Avian Proteins/genetics/metabolism ; Beak/*anatomy & histology ; Ecuador ; *Evolution, Molecular ; Female ; Finches/*anatomy & histology/classification/embryology/*genetics ; Gene Flow ; Genome/genetics ; Haplotypes/genetics ; Hybridization, Genetic ; Indian Ocean Islands ; Male ; Molecular Sequence Data ; Phylogeny ; Transcription Factors/genetics/metabolism

2014-03-14

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

Animals ; Female ; *Hybridization, Genetic ; Male ; *Mating Preference, Animal ; Songbirds/*genetics

2016-04-23

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Animals ; Beak/*anatomy & histology ; Body Size/genetics ; *Droughts ; Ecuador ; Female ; Finches/*anatomy & histology/classification/*genetics ; Genomics ; Genotype ; HMGA2 Protein/genetics ; Haplotypes ; Organ Size/genetics ; Phylogeny ; *Quantitative Trait Loci ; *Selection, Genetic

2018-01-12

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Geosciences

Computer Science

Medicine

Natural Sciences in General

Physics

Evolution, Genetics

1432-1939

Springer Online Journal Archives 1860-2000

Biology

Summary (1) We report some effects of an annually variable and unpredictable rainfall upon Darwin's Finches on the Galápagos. Finch numbers, foraging and food supply were studied on I. Daphne Major in December of 1973 and 1977, and compared. 1973 was the second of two successive wet years and 1977 was a drought year. (2) Seed numbers and biomass were approximately one order of magnitude lower in the drought year than in the wet year. Small and soft seeds were absolutely and relatively rarer in the drought year than in the wet year. (3) Similarly finch numbers and biomass were approximately one order of magnitude lower in the drought year than in the wet year. Numbers of G. scandens declined less than did number of G. fortis. Both species exhibited unabalaced sex ratios, in favour of males, in the dry year in contrast to balanced sex ratios in the wet year. Male scandens were heavier on average in the wet year, but male fortis were heavier in the dry year. (4) The foraging of scandens, a cactus (Opuntia) specialist, was similar in the two years. The foraging of fortis in the dry year differed from foraging in the wet year in three important respects: fortis devoted a disproportionate amount of time to feeding on small seeds while tending to avoid seeds of Opuntia, they fed more on floral and extra-floral parts of Opuntia and they fed on Tribulus cistoides, a large and hard fruit which was absent from their diet in the wet year. As a consequence of feeding more on Opuntia, fortis foraging was more similar to scandens foraging in the dry year than in the wet year. (5) The results are discussed in relation to expectations from competition theory. The decline in numbers in relation to a decline in food supply was expected, but a convergence in diets was not. The convergence is attributed to the recent renewal of a single resource, Opuntia flowers, against a background of general resource scarcity. Diet overlap and limitation of numbers by food provide indirect evidence of interspecific competition; scandens, with an included niche, was competitively superior to fortis.

Electronic Resource

1432-1939

Springer Online Journal Archives 1860-2000

Biology

Summary (1) There is a close association between Opuntia helleri (cactus) and Geospiza conirostris (cactus finch) on Isla Genovesa, and between Opuntia echios and Geospiza scandens on Isla Daphne Major. The two finch species consume nectar and pollen, pollinate the obligatorily out-crossing flowers, consume the aril around the seeds, crack the seeds and occasionally disperse them. (2) In the dry season the two finch species open Opuntia flower buds, thereby gaining early access to pollen. But in the process, and at partially open flowers, they snip the style and destroy the stigmas in up to 78% of the flowers. (3) Stigma snipping prevents fertilization of the ovules and the development of seeds which are an important food item later in the year when food supply is likely to limit finch population sizes. Stigma snipping almost ceases in the main part of the wet season, corresponding with an increase in the density of Opuntia flowers and other food types, and a decrease in the proportion of feeding time spent on Opuntia flowers. Stigma snipping neither increased the time flowers remained open nor influenced nectar flow or the number and duration of subsequent visits to flowers by potential pollinators. This last result precludes the possibility that snipping is a means of marking the flower to signal a previous visit to the flower and pollen removal. (4) We conclude that the two finch species snip stigmas to facilitate removal of pollen from the central incurving stamens which are masked by the stigma in a closed or partially open flower. The finches gain a short-term benefit from the removal of stigmas in easy access to pollen and possibly nectar. They potentially suffer in the long term through diminished dry season food supply (seeds), particularly in drought years but we were unable to detect any fitness decrement suffered by the individual finches which do the snipping. (5) An important implication of these results and interpretations is that a behavioral trait which confers a short-term benefit to the individual may increase the chances of the population going extinct.

Electronic Resource

1432-1939

Springer Online Journal Archives 1860-2000

Biology

Summary In this study we investigated the relationship between food availability, feeding ecology and territoriality in a population of Cactus Finches, Geospiza scandens, on Isla Daphne Major, Galápagos, between 1979 and 1981. We monitored the phenologies of the principal food types on the island and related them to changes in the feeding ecology of G. scandens. Feeding patterns closely tracked the availability of resources, with a similar pattern in each of the three years. Birds relied heavily on Opuntia fruits in the dry season. G. scandens defends year-round territories based on Opuntia. Variation in Opuntia phenologies between individual territories and between years was documented in order to provide a measure of territory quality over the three years. A correlation was demonstrated between the area of cactus within a territory and mating success of the owner. We suggest that territory quality also affects the survival of the owners during periods of food scarcity and that the mating and survival advantage of a high-quality territory occur at different times and to different degrees in different years. Hence the importance of territorial quality can only be judged over a long-term period in these long lived and sedentary birds.

Electronic Resource

1432-1939

Springer Online Journal Archives 1860-2000

Biology

Summary Populations of 4 geospizine finches were studied on Isla Daphne Major in April and December 1973. Finches were captured, banded, measured and released in both months, and censused in December. 1640±711 finches were estimated to be present in December, of which probably more than 1000 belonged to Geospiza fortis. G. fortis were 4 times more numerous than G. scandens. The overal density at this time was 27–54/ha. This is the first quantitative estimate of finch population sizes for a whole island in the Galápagos Archipelago. Some G. fuliginosa and magnirostris immigrated between study periods, but overall density remained nearly constant. There was no evidence of immigration of fortis and scandens. Survival rates of the two common species, fortis and scandens, from April to December were estimated, from banded birds, to be 86.9% and 91.3%. Up to 300 finches (fortis and scandens) disappeared between study periods. The amount of predation by owls (Asio flammeus), estimated from an analysis of 49 pellets, could account for more than 50% of the finch losses, but is likely to be less. The estimated loss due to predation was less than 10% of the populations in April. The discovery of the remains of house mice, Mus musculus, and black rats, Rattus rattus, in pellets indicates that owls hunt on one island (e.g. Santa Cruz or Baltra) and regurgitate on another (Daphne). Fruits of a Euphorb, Chamaesyce amplexicaulis (Hook. f.) Burch, that finches eat were found in two pellets that also contained finch remains. This suggests that seeds or fruits in the throat of a victim at the time of a kill may be transported unharmed inside an owl from one island to another. Indirect support to this suggestion is given by the results of flotation experiments with seeds and fruits of 22 species of plants. Most did not float, and are too heavy to be transported by normal winds. Many do not have hooks or sticky surfaces, and internal transport by birds (including owls) is therefore strongly suggested.

Electronic Resource