scholarly journals Climate, ecological release and bill dimorphism in an island songbird

2013 ◽  
Vol 9 (3) ◽  
pp. 20130118 ◽  
Author(s):  
Russell Greenberg ◽  
Raymond M. Danner
Keyword(s):  
Interspecific Competition ◽  
Positive Temperature ◽  
Island Size ◽  
Ecological Release ◽  
Size Dimorphism ◽  
Island Populations ◽  
Song Sparrows ◽  
Summer Heat ◽  
High Summer Temperature ◽  
Competition For Food

Sexual size dimorphism is expected to be more pronounced in vertebrates on islands, particularly in trophic characters, as a response to decreased interspecific competition for food. We found (based on measurements of 1423 museum specimens) that bill size dimorphism was greater in island than mainland populations of song sparrows. However, dimorphism varied among islands and was positively correlated with high summer temperature and island size. Island song sparrow bills follow the overall positive temperature bill size relationship for California song sparrows, which includes larger bills on large, warmer islands. Large bills dissipate more heat and may be an adaptation to summer heat stress. Dimorphism increases because the slope for males is greater than females. Thus, the greater magnitude of bill dimorphism on islands with warmer summers may result from males experiencing greater thermal stress during territorial activity, creating different thermal optima. In contrast, bill dimorphism was unrelated to climate on the mainland. We hypothesize that reduced interspecific competition releases island populations from a constraint so that sex-specific physiological optima can be achieved, whereas mainland birds are constrained.

scholarly journals Avian succession along ecological gradients: Insight from species-poor and species-rich communities of Sylvia warblers

2011 ◽  
Vol 57 (3) ◽  
pp. 307-317 ◽  
Author(s):  
Alban Guillaumet ◽  
Roger Prodon
Keyword(s):  
Interspecific Competition ◽  
Species Turnover ◽  
Predictive Ability ◽  
Distribution Model ◽  
Joint Analysis ◽  
Data Sets ◽  
Ecological Gradients ◽  
Distribution Models ◽  
Ecological Release ◽  
Low Diversity

Abstract The mechanisms responsible for species replacement during ecological successions is a long-standing and open debate. In this study, we examined the distribution of the Sardinian warbler Sylvia melanocephala along two grassland-to-forest gradients, one in a high-diversity area (Albera-Aspres chain in Catalonia: eight Sylvia warbler species) and one in a low-diversity area (Mount Hymittos in Greece: four species). In Catalonia, distribution models suggested that the apparent exclusion of S. melanocephala from the open and forest ends of the gradient may be explained entirely by the preference of S. melanocephala for mid-successional shrublands. However, a joint analysis of both data sets revealed that: 1) S. melanocephala was more evenly distributed along the vegetation gradient in Greece, suggesting ecological release in the low-diversity area; and 2) a distribution model assuming interspecific competition (based on the distribution of Sylvia species showing a negative co-occurrence pattern with S. melanocephala) had a significantly higher predictive ability than a distribution model based on habitat variables alone. Our study supports the view that species turnover along ecological gradients generally results from a combination of intrinsic preferences and interspecific competition.

scholarly journals Population Genetics of the Galápagos Hawk (Buteo Galapagoensis): Genetic Monomorphism Within Isolated Populations

The Auk ◽  
2005 ◽  
Vol 122 (4) ◽  
pp. 1210-1224 ◽  
Author(s):  
Jennifer L. Bollmer ◽  
Noah K. Whiteman ◽  
Michelle D. Cannon ◽  
James C. Bednarz ◽  
Tjitte de Vries ◽  
...  
Keyword(s):  
Genetic Drift ◽  
Dna Markers ◽  
Entire Range ◽  
Genetic Similarity ◽  
Isolated Populations ◽  
Island Size ◽  
Bird Population ◽  
Island Populations ◽  
Genetic Uniformity ◽  
Cooperative Polyandry

Abstract Because of their smaller size and isolation, island populations tend to be more divergent and less genetically variable than mainland populations. We collected DNA samples from nine Galápagos Hawk (Buteo galapagoensis) island populations, covering the species’ entire range. Neutral minisatellite DNA markers were used to calculate within-island genetic diversity and between-island genetic differentiation (FST). Typically, these markers mutate too quickly to be informative in such studies. However, in very small, isolated populations, concerns about high mutational rate are obviated by the relative force of genetic drift. Individuals within islands had the highest levels of reported genetic uniformity of any natural bird population, with mean within-population band-sharing similarity values ranging from 0.693 to 0.956, increasing with decreasing island size. Galápagos Hawks exhibit cooperative polyandry to varying degrees across islands; however, we did not find an association between degree of polyandry and genetic variability. Between-island FST values ranged from 0.017 to 0.896, with an overall archipelago value of 0.538; thus, most populations were genetically distinct. Also, we documented higher levels of genetic similarity between nearby populations. Our results indicated negligible gene flow among most Galápagos Hawk populations, and genetic drift has played a strong role in determining structure at these minisatellite loci. Genética de Poblaciones de Buteo galapagoensis: Monomorfismo Genético dentro de Poblaciones Aisladas

scholarly journals Differentiation with drift: a spatio-temporal genetic analysis of Galápagos mockingbird populations ( Mimus spp.)

2010 ◽  
Vol 365 (1543) ◽  
pp. 1127-1138 ◽  
Author(s):  
Paquita E. A. Hoeck ◽  
Jennifer L. Bollmer ◽  
Patricia G. Parker ◽  
Lukas F. Keller
Keyword(s):  
Genetic Diversity ◽  
Gene Flow ◽  
Population Size ◽  
Genetic Drift ◽  
Bird Species ◽  
Effective Population ◽  
Island Size ◽  
Island Populations ◽  
Population Sizes ◽  
Spatio Temporal

Small and isolated island populations provide ideal systems to study the effects of limited population size, genetic drift and gene flow on genetic diversity. We assessed genetic diversity within and differentiation among 19 mockingbird populations on 15 Galápagos islands, covering all four endemic species, using 16 microsatellite loci. We tested for signs of drift and gene flow, and used historic specimens to assess genetic change over the last century and to estimate effective population sizes. Within-population genetic diversity and effective population sizes varied substantially among island populations and correlated strongly with island size, suggesting that island size serves as a good predictor for effective population size. Genetic differentiation among populations was pronounced and increased with geographical distance. A century of genetic drift did not change genetic diversity on an archipelago-wide scale, but genetic drift led to loss of genetic diversity in small populations, especially in one of the two remaining populations of the endangered Floreana mockingbird. Unlike in other Galápagos bird species such as the Darwin's finches, gene flow among mockingbird populations was low. The clear pattern of genetically distinct populations reflects the effects of genetic drift and suggests that Galápagos mockingbirds are evolving in relative isolation.

scholarly journals Variation in Morphology and Mating System Among Island Populations of GaláPagos Hawks

The Condor ◽  
2003 ◽  
Vol 105 (3) ◽  
pp. 428-438 ◽  
Author(s):  
Jennifer L. Bollmer ◽  
Tania Sanchez ◽  
Michelle Donaghy Cannon ◽  
Didier Sanchez ◽  
Brian Cannon ◽  
...  
Keyword(s):  
Body Size ◽  
Mating System ◽  
Sexual Size Dimorphism ◽  
Negative Relationship ◽  
Interspecific Variation ◽  
Size Dimorphism ◽  
Island Populations ◽  
Cooperative Polyandry ◽  
El Sistema ◽  
Los Grupos

Abstract Interspecific variation in sexual size dimorphism has commonly been attributed to variation in social mating system, with dimorphism increasing as intrasexual competition for mates increases. In birds, overall body size has also been found to correlate positively with size dimorphism. In this study, we describe variation in morphology and mating system across six populations of the endemic Galápagos Hawk (Buteo galapagoensis). Galápagos Hawks exhibit cooperative polyandry, a mating system in which long-term social groups contain a single female and multiple males. Comparisons among islands revealed significant differences in overall body size for both adults and immatures. Populations ranged from completely monogamous to completely polyandrous, with varying mean group sizes. Data did not support our prediction that sexual size dimorphism would increase with the degree of polyandry (number of males per group) or with body size; there was no correlation between mating system and sexual dimorphism. We did find a significant negative relationship between degree of polyandry and body size among islands, opposite of the pattern predicted. Variación en Morfología y Sistema de Apareamiento entre Poblaciones de Buteo galapagoensis Resumen. Variación interespecífica en dimorfismo sexual ha sido atribuída comúnmente a variaciones del sistema social de apareamiento, de tal manera que el dimorfismo aumenta conforme aumenta la competencia intrasexual por parejas reproductivas. También se ha encontrado que el tamaño corporal se correlaciona positivamente con el dimorfismo. En este estudio describimos la variación morfológica y el grado de poliandría de seis poblaciones de Buteo galapagoensis, una especie que exhibe un sistema de apareamiento denominado poliandría cooperativa. En este sistema los grupos de individuos reproductivos incluyen una sola hembra y múltiples machos. Se comprobó que existen diferencias significativas en el tamaño del cuerpo de adultos y juveniles entre islas. Las poblaciones muestreadas variaron entre monógamas y completamente poliándricas, y el tamaño promedio de los grupos fue variable. Los datos no apoyaron las predicciones establecidas inicialmente pues el grado de dimorfismo sexual no aumentó con el nivel de poliandría (número de machos por grupo) ni con el tamaño corporal, ni hubo una correlación entre el sistema de apareamiento y el dimorfismo sexual. La relación entre el tamaño corporal y el sistema de apareamiento fue contraria a la que se predijo: hubo una correlación negativa significativa entre el grado de poliandría y el tamaño corporal entre islas.

Environmental factors affecting sexual size dimorphism in the hermit crab Pagurus middendorffii

1999 ◽  
Vol 79 (5) ◽  
pp. 953-954 ◽  
Author(s):  
Satoshi Wada
Keyword(s):  
Environmental Factors ◽  
Interspecific Competition ◽  
Hermit Crab ◽  
Sexual Size Dimorphism ◽  
Sympatric Species ◽  
Shell Size ◽  
Male And Female ◽  
Factors Affecting ◽  
Size Dimorphism ◽  
Population Comparisons

The effects of shell resource and interspecific competition on sexual size dimorphism of the hermit crab, Pagurus middendorffii (Decapoda: Paguridae), were examined from population comparisons. Degree of size dimorphism and mean shell size occupied by male and female P. middendorffii differed among adjacent sites, and there was a significant correlation between them. Although most large P. middendorffii occupied large Chlorostoma lischkei shells in both shell-limited and shell-unlimited populations, P. lanuginosus, a sympatric species, occupied large C. lischkei shells more frequently than P. middendorffii did in a shell-limited population. Environmental factors, shell availability and interspecific competition for shells, might play important roles in determining the degree of sexual size dimorphism of P. middendorffii.

Feeding relationships between sympatric Afrotropical tree frogs (genus Hyperolius): The effects of predator body size and season

2004 ◽  
Vol 54 (3) ◽  
pp. 293-302 ◽  
Author(s):  
◽  
◽  
◽  
◽  
◽  
...  
Keyword(s):  
Interspecific Competition ◽  
Diet Composition ◽  
Sexual Size Dimorphism ◽  
Stomach Contents ◽  
The Other ◽  
Size Dimorphism ◽  
Frog Species ◽  
Tree Frogs ◽  
The One ◽  
Average Size

AbstractThe feeding relationships of four sympatric, ecologically nearly unknown, tree frogs of southern Nigeria (Hyperolius sylvaticus, H. guttulatus, H. fusciventris burtoni, and H. concolor) were studied during both the dry and the rainy seasons. Stomach contents were obtained by stomach flushing. The largest species were H. guttulatus and H. concolor, whereas the other two species were of smaller average size. A statistically significant sexual size dimorphism was observed in H. guttulatus, H. concolor, and H. sylvaticus (in all species the females were larger), but not in H. fusciventris. In all four species, the frequency of animals with empty stomachs was significantly lower during the rainy season than during the dry season. The four frog species were mainly arthropodeating: Araneidae and Blattoidea were preyed upon mainly by the two largest species, Acarina and Lepidoptera were taken mainly by the two smaller species, and Diptera and Formicoidea were eaten frequently by all species. The diet composition was similar between seasons in three of the four species, and H. guttulatus was the only species showing considerable diet variation between seasons. We concluded that 1) the intensity of interspecific competition should be particularly high between the two larger species on the one hand, and between the two smaller species on the other hand; and 2) the intensity of the interspecific competition should be relatively constant throughout the year.

scholarly journals Insularity induces changes on body and mandible morphology in a Mediterranean population of the greater white-toothed shrew Crocidura russula (Hermann, 1780)

2018 ◽  
Vol 87 (4) ◽  
pp. 275-286
Author(s):  
Alejandro Sánchez-Chardi ◽  
Marian García-Pando ◽  
Eudald Pujol-Buxó ◽  
Maria A. Sans-Fuentes ◽  
María José López-Fuster ◽  
...  
Keyword(s):  
Interspecific Competition ◽  
Body Condition ◽  
Intraspecific Competition ◽  
Direct Result ◽  
Island Population ◽  
Mediterranean Population ◽  
Island Populations ◽  
Terrestrial Mammals ◽  
Crocidura Russula ◽  
Mandible Shape

Island populations of terrestrial mammals often undergo extensive behavioural and morphological changes when separated from mainland populations. Within small mammals these changes have been mainly reported in rodents but were poorly assessed in soricomorphs. In this study we compared mandible morphology and body condition between mainland and island populations of the greater white-toothed shrew, Crocidura russula. The results indicated that island specimens were bigger and heavier than the mainland counterpart, and they showed changes in mandible shape that were associated with higher mechanical potentials. We suggest that these changes might be the result of the interaction of two main factors taking place in the island population: ecological release (i.e. the decrease of predation and interspecific competition), and consequently the increase of intraspecific competition. While the increase in size and body condition in island shrews could be a direct result from reduced predation and interspecific competition, the changes in mandible shape and the increase of both mechanical potential and sexual dimorphism could have arisen indirectly as a response to stronger intraspecific competition.

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