scholarly journals Disruptive selection in a bimodal population of Darwin's finches

2008 ◽  
Vol 276 (1657) ◽  
pp. 753-759 ◽  
Author(s):  
Andrew P Hendry ◽  
Sarah K Huber ◽  
Luis F De León ◽  
Anthony Herrel ◽  
Jeffrey Podos
Keyword(s):  
Adaptive Radiation ◽  
Spatial And Temporal Variation ◽  
Disruptive Selection ◽  
Adaptive Divergence ◽  
Santa Cruz Island ◽  
Santa Cruz ◽  
Prolonged Drought ◽  
Geospiza Fortis ◽  
Beak Size ◽  
Insight Into

A key part of the ecological theory of adaptive radiation is disruptive selection during periods of sympatry. Some insight into this process might be gained by studying populations that are bimodal for dual-context traits, i.e. those showing adaptive divergence and also contributing to reproductive isolation. A population meeting these criteria is the medium ground finch ( Geospiza fortis ) of El Garrapatero, Santa Cruz Island, Galápagos. We examined patterns of selection in this population by relating individual beak sizes to interannual recaptures during a prolonged drought. Supporting the theory, disruptive selection was strong between the two beak size modes. We also found some evidence of selection against individuals with the largest and smallest beak sizes, perhaps owing to competition with other species or to gaps in the underlying resource distribution. Selection may thus simultaneously maintain the current bimodality while also constraining further divergence. Spatial and temporal variation in G. fortis bimodality suggests a dynamic tug of war among factors such as selection and assortative mating, which may alternatively promote or constrain divergence during adaptive radiation.

scholarly journals Acoustic discrimination of sympatric morphs in Darwin's finches: a behavioural mechanism for assortative mating?

2010 ◽  
Vol 365 (1543) ◽  
pp. 1031-1039 ◽  
Author(s):  
Jeffrey Podos
Keyword(s):  
Assortative Mating ◽  
Disruptive Selection ◽  
Evolutionary Divergence ◽  
Santa Cruz Island ◽  
Evolutionary Diversification ◽  
Acoustic Discrimination ◽  
Behavioural Types ◽  
Geospiza Fortis ◽  
Beak Size ◽  
Behavioural Mechanism

Populations with multiple morphological or behavioural types provide unique opportunities for studying the causes and consequences of evolutionary diversification. A population of the medium ground finch ( Geospiza fortis ) at El Garrapatero on Santa Cruz Island, Galápagos, features two beak size morphs. These morphs produce acoustically distinctive songs, are subject to disruptive selection and mate assortatively by morph. The main goal of the present study was to assess whether finches from this population are able to use song as a cue for morph discrimination. A secondary goal of this study was to evaluate whether birds from this population discriminate songs of their own locality versus another St Cruz locality, Borrero Bay, approximately 24 km to the NW. I presented territorial males with playback of songs of their own morph, of the other morph, and of males from Borrero Bay. Males responded more strongly to same-morph than to other-morph playbacks, showing significantly shorter latencies to flight, higher flight rates and closer approaches to the playback speaker. By contrast, I found only minor effects of locality on responsiveness. Evidence for morph discrimination via acoustic cues supports the hypothesis that song can serve as a behavioural mechanism for assortative mating and sympatric evolutionary divergence.

scholarly journals Possible human impacts on adaptive radiation: beak size bimodality in Darwin's finches

2006 ◽  
Vol 273 (1596) ◽  
pp. 1887-1894 ◽  
Author(s):  
Andrew P Hendry ◽  
Peter R Grant ◽  
B Rosemary Grant ◽  
Hugh A Ford ◽  
Mark J Brewer ◽  
...  
Keyword(s):  
Adaptive Radiation ◽  
Human Activities ◽  
Human Impacts ◽  
Adaptive Landscape ◽  
Hybrid Fitness ◽  
Evolutionary Diversification ◽  
Adaptive Landscapes ◽  
Adaptive Radiations ◽  
Geospiza Fortis ◽  
Beak Size

Adaptive radiation is facilitated by a rugged adaptive landscape, where fitness peaks correspond to trait values that enhance the use of distinct resources. Different species are thought to occupy the different peaks, with hybrids falling into low-fitness valleys between them. We hypothesize that human activities can smooth adaptive landscapes, increase hybrid fitness and hamper evolutionary diversification. We investigated this possibility by analysing beak size data for 1755 Geospiza fortis measured between 1964 and 2005 on the island of Santa Cruz, Galápagos. Some populations of this species can display a resource-based bimodality in beak size, which mirrors the greater beak size differences among species. We first show that an historically bimodal population at one site, Academy Bay, has lost this property in concert with a marked increase in local human population density. We next show that a nearby site with lower human impacts, El Garrapatero, currently manifests strong bimodality. This comparison suggests that bimodality can persist when human densities are low (Academy Bay in the past, El Garrapatero in the present), but not when they are high (Academy Bay in the present). Human activities may negatively impact diversification in ‘young’ adaptive radiations, perhaps by altering adaptive landscapes.

scholarly journals Temporally varying disruptive selection in the medium ground finch ( Geospiza fortis )

2019 ◽  
Vol 286 (1916) ◽  
pp. 20192290 ◽  
Author(s):  
Marc-Olivier Beausoleil ◽  
Luke O. Frishkoff ◽  
Leithen K. M'Gonigle ◽  
Joost A. M. Raeymaekers ◽  
Sarah A. Knutie ◽  
...  
Keyword(s):  
Population Differentiation ◽  
Climatic Factors ◽  
Fitness Function ◽  
Disruptive Selection ◽  
Trait Variation ◽  
Fitness Functions ◽  
Time Period ◽  
Geospiza Fortis ◽  
Beak Size

Disruptive natural selection within populations exploiting different resources is considered to be a major driver of adaptive radiation and the production of biodiversity. Fitness functions, which describe the relationships between trait variation and fitness, can help to illuminate how this disruptive selection leads to population differentiation. However, a single fitness function represents only a particular selection regime over a single specified time period (often a single season or a year), and therefore might not capture longer-term dynamics. Here, we build a series of annual fitness functions that quantify the relationships between phenotype and apparent survival. These functions are based on a 9-year mark–recapture dataset of over 600 medium ground finches ( Geospiza fortis ) within a population bimodal for beak size. We then relate changes in the shape of these functions to climate variables. We find that disruptive selection between small and large beak morphotypes, as reported previously for 2 years, is present throughout the study period, but that the intensity of this selection varies in association with the harshness of environment. In particular, we find that disruptive selection was strongest when precipitation was high during the dry season of the previous year. Our results shed light on climatic factors associated with disruptive selection in Darwin's finches, and highlight the role of temporally varying fitness functions in modulating the extent of population differentiation.

scholarly journals Body size, sex and high philopatry influence the use of agricultural land by Galapagos giant tortoises

Oryx ◽  
2021 ◽  
pp. 1-10
Author(s):  
Kyana N. Pike ◽  
Stephen Blake ◽  
Freddy Cabrera ◽  
Iain J. Gordon ◽  
Lin Schwarzkopf
Keyword(s):  
National Park ◽  
Agricultural Land ◽  
Large Male ◽  
Gps Data ◽  
Santa Cruz Island ◽  
Santa Cruz ◽  
Agricultural Areas ◽  
On Farm ◽  
Human Wildlife Conflict ◽  
Privately Owned

Abstract As agricultural areas expand, interactions between wild animals and farmland are increasing. Understanding the nature of such interactions is vital to inform the management of human–wildlife coexistence. We investigated patterns of space use of two Critically Endangered Galapagos tortoise species, Chelonoidis porteri and Chelonoidis donfaustoi, on privately owned and agricultural land (hereafter farms) on Santa Cruz Island, where a human–wildlife conflict is emerging. We used GPS data from 45 tortoises tracked for up to 9 years, and data on farm characteristics, to identify factors that influence tortoise movement and habitat use in the agricultural zone. Sixty-nine per cent of tagged tortoises used the agricultural zone, where they remained for a mean of 150 days before returning to the national park. Large male tortoises were more likely to use farms for longer periods than female and smaller individuals. Tortoises were philopatric (mean overlap of farmland visits = 88.7 ± SE 2.9%), on average visiting four farms and occupying a mean seasonal range of 2.9 ± SE 0.3 ha. We discuss the characteristics of farm use by tortoises, and its implications for tortoise conservation and coexistence with people.

scholarly journals Isotopic Niche Segregation among Darwin’s Finches on Santa Cruz Island, Galápagos

Diversity ◽  
2021 ◽  
Vol 13 (4) ◽  
pp. 147
Author(s):  
Mariana Villegas ◽  
Catherine Soos ◽  
Gustavo Jiménez-Uzcátegui ◽  
Shukri Matan ◽  
Keith A. Hobson
Keyword(s):  
Three Dimensional ◽  
Sympatric Species ◽  
Isotopic Niche ◽  
Museum Specimens ◽  
Santa Cruz Island ◽  
Santa Cruz ◽  
Δ13c And Δ15n ◽  
Darwin's Finches ◽  
Darwin’S Finches ◽  
Foraging Guilds

Darwin’s finches are a classic example of adaptive radiation involving differential use of dietary resources among sympatric species. Here, we apply stable isotope (δ13C, δ15N, and δ2H) analyses of feathers to examine ecological segregation among eight Darwin’s finch species in Santa Cruz Island, Galápagos collected from live birds and museum specimens (1962–2019). We found that δ13C values were higher for the granivorous and herbivorous foraging guilds, and lower for the insectivorous finches. Values of δ15N were similar among foraging guilds but values of δ2H were higher for insectivores, followed by granivores, and lowest for herbivores. The herbivorous guild generally occupied the largest isotopic standard ellipse areas for all isotopic combinations and the insectivorous guild the smallest. Values of δ2H provided better trophic discrimination than those of δ15N possibly due to confounding influences of agricultural inputs of nitrogen. Segregation among guilds was enhanced by portraying guilds in three-dimensional isotope (δ13C, δ15N, and δ2H) space. Values of δ13C and δ15N were higher for feathers of museum specimens than for live birds. We provide evidence that Darwin’s finches on Santa Cruz Island tend to be generalists with overlapping isotopic niches and suggest that dietary overlap may also be more considerable than previously thought.

scholarly journals SEROLOGIC SURVEY OF THE ISLAND SPOTTED SKUNK ON SANTA CRUZ ISLAND

2006 ◽  
Vol 66 (4) ◽  
pp. 456-461 ◽  
Author(s):  
Victoria J. Bakker ◽  
Dirk H. Van Vuren ◽  
Kevin R. Crooks ◽  
Cheryl A. Scott ◽  
Jeffery T. Wilcox ◽  
...  
Keyword(s):  
Santa Cruz Island ◽  
Santa Cruz ◽  
Serologic Survey
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