scholarly journals Mapping of dextral : sinistral proportions in the chirally dimorphic land snail Amphidromus inversus

2014 ◽  
Author(s):  
Menno Schilthuizen ◽  
Sylvia Looijestijn ◽  
Sek Chuan Chua ◽  
Ruth F. Castillo Cajas
Keyword(s):  
Population Structure ◽  
Vegetation Structure ◽  
Predation Rate ◽  
Land Snail ◽  
Mirror Image ◽  
Single Population ◽  
Modelling Studies ◽  
Vegetation Parameters ◽  
Genetically Determined ◽  
Predation Rates

One of the very few snail taxa that display genetic antisymmetry (that is, roughly even mixes of genetically determined clockwise and anticlockwise individuals within a single population) are the circa 35 species of the tropical tree snail subgenus Amphidromus. Previous work has shown that this may be due to a particular type of sexual selection, in which sperm transfer is improved in copulations between the two mirror-image morphs. However, it is not yet clear why so often significant deviations from 50:50 proportions are found. Modelling studies show that population structure will affect the degree by which the dimorphism is skewed towards the morph associated with the recessive allele. In this study, we mapped the proportions of sinistrals (PropS) in 56 demes in A. inversus on the Malaysian island of Kapas. We also mapped population density, predation rates, and several measures of vegetation structure. Our results show that PropS amounts on average to 0.65, but across the island varies from 0.30 to 0.85. Density and overall predation are inversely correlated, but neither predicts PropS. Vegetation parameters also do not correlate with the proportion of sinistrals. We do, however, find a negative correlation between the predation rate on sinistrals and PropS, a finding which may warrant further study.

scholarly journals Mapping of dextral : sinistral proportions in the chirally dimorphic land snail Amphidromus inversus

2015 ◽  
Author(s):  
Menno Schilthuizen ◽  
Sylvia Looijestijn ◽  
Sek Chuan Chua ◽  
Jesús Aguirre Gutiérrez ◽  
Ruth F. Castillo Cajas
Keyword(s):  
Vegetation Structure ◽  
Selection Procedure ◽  
General Linear Model ◽  
Land Snail ◽  
Mirror Image ◽  
Single Population ◽  
Overwhelming Evidence ◽  
Modelling Studies ◽  
Genetically Determined ◽  
Predation Rates

One of the very few snail taxa that display genetic antisymmetry (that is, roughly equal mixes of genetically determined clockwise [D] and anticlockwise [S] coiled individuals within a single population) are the circa 35 species of the tropical tree snail subgenus Amphidromus. Previous work has shown that this may be due to a particular type of sexual selection, in which sperm transfer is improved in copulations between the two mirror-image morphs. However, it is not yet clear why so often significant deviations from 50:50 proportions are found. Modelling studies show that population structure will affect the degree by which the dimorphism is skewed towards the morph associated with the recessive allele. In this study, we mapped the proportions of sinistrals (PropS) in 56 demes in A. inversus on the Malaysian island of Kapas. We also mapped population density, predation rates, and several measures of vegetation structure. Our results show that PropS amounts on average to 0.65, but across the island it varies from 0.30 to 0.85. Density and overall predation are inversely correlated. A general linear model selection procedure results in the proportion of sinistrals to be positively correlated with density and predation on dextrals. We find no overwhelming evidence for a role for drift in explaining the deviations from equal S:D proportions, but we do argue that further study of crab-snail interactions may be warranted.

scholarly journals Mapping of dextral : sinistral proportions in the chirally dimorphic land snail Amphidromus inversus

2015 ◽  
Author(s):  
Menno Schilthuizen ◽  
Sylvia Looijestijn ◽  
Sek Chuan Chua ◽  
Jesús Aguirre Gutiérrez ◽  
Ruth F. Castillo Cajas
Keyword(s):  
Vegetation Structure ◽  
Selection Procedure ◽  
General Linear Model ◽  
Land Snail ◽  
Mirror Image ◽  
Single Population ◽  
Overwhelming Evidence ◽  
Modelling Studies ◽  
Genetically Determined ◽  
Predation Rates

One of the very few snail taxa that display genetic antisymmetry (that is, roughly equal mixes of genetically determined clockwise [D] and anticlockwise [S] coiled individuals within a single population) are the circa 35 species of the tropical tree snail subgenus Amphidromus. Previous work has shown that this may be due to a particular type of sexual selection, in which sperm transfer is improved in copulations between the two mirror-image morphs. However, it is not yet clear why so often significant deviations from 50:50 proportions are found. Modelling studies show that population structure will affect the degree by which the dimorphism is skewed towards the morph associated with the recessive allele. In this study, we mapped the proportions of sinistrals (PropS) in 56 demes in A. inversus on the Malaysian island of Kapas. We also mapped population density, predation rates, and several measures of vegetation structure. Our results show that PropS amounts on average to 0.65, but across the island it varies from 0.30 to 0.85. Density and overall predation are inversely correlated. A general linear model selection procedure results in the proportion of sinistrals to be positively correlated with density and predation on dextrals. We find no overwhelming evidence for a role for drift in explaining the deviations from equal S:D proportions, but we do argue that further study of crab-snail interactions may be warranted.

scholarly journals Effects of habitat edges on vegetation structure and the vulnerable golden-brown mouse lemur (Microcebus ravelobensis) in northwestern Madagascar

BMC Ecology ◽  
2020 ◽  
Vol 20 (1) ◽  
Author(s):  
Bertrand Andriatsitohaina ◽  
Daniel Romero-Mujalli ◽  
Malcolm S. Ramsay ◽  
Frederik Kiene ◽  
Solofonirina Rasoloharijaona ◽  
...  
Keyword(s):  
Body Mass ◽  
Edge Effects ◽  
Vegetation Structure ◽  
Species Abundance ◽  
Tree Height ◽  
Logistic Function ◽  
Study Region ◽  
Large Trees ◽  
Significant Difference ◽  
Vegetation Parameters

Abstract Background Edge effects can influence species composition and community structure as a result of changes in microenvironment and edaphic variables. We investigated effects of habitat edges on vegetation structure, abundance and body mass of one vulnerable Microcebus species in northwestern Madagascar. We trapped mouse lemurs along four 1000-m transects (total of 2424 trap nights) that ran perpendicular to the forest edge. We installed 16 pairs of 20 m2 vegetation plots along each transect and measured nine vegetation parameters. To determine the responses of the vegetation and animals to an increasing distance to the edge, we tested the fit of four alternative mathematical functions (linear, power, logistic and unimodal) to the data and derived the depth of edge influence (DEI) for all parameters. Results Logistic and unimodal functions best explained edge responses of vegetation parameters, and the logistic function performed best for abundance and body mass of M. ravelobensis. The DEI varied between 50 m (no. of seedlings, no. of liana, dbh of large trees [dbh ≥ 10 cm]) and 460 m (tree height of large trees) for the vegetation parameters, whereas it was 340 m for M. ravelobensis abundance and 390 m for body mass, corresponding best to the DEI of small tree [dbh < 10 cm] density (360 m). Small trees were significantly taller and the density of seedlings was higher in the interior than in the edge habitat. However, there was no significant difference in M. ravelobensis abundance and body mass between interior and edge habitats, suggesting that M. ravelobensis did not show a strong edge response in the study region. Finally, regression analyses revealed three negative (species abundance and three vegetation parameters) and two positive relationships (body mass and two vegetation parameters), suggesting an impact of vegetation structure on M. ravelobensis which may be partly independent of edge effects. Conclusions A comparison of our results with previous findings reveals that edge effects are variable in space in a small nocturnal primate from Madagascar. Such an ecological plasticity could be extremely relevant for mitigating species responses to habitat loss and anthropogenic disturbances.

scholarly journals Does human influence on coastal grasslands habitats affect predation pressure on snakes?

2013 ◽  
Vol 13 (1) ◽  
pp. 366-370 ◽  
Author(s):  
Mauricio Beux dos Santos ◽  
Mauro Cesar Lamim Martins de Oliveira ◽  
Tatiane Penteado Gonçalves ◽  
Francis de Mattos Almeida ◽  
Daniel Loebmann ◽  
...  
Keyword(s):  
South America ◽  
Interspecific Interactions ◽  
Predation Rate ◽  
Predation Pressure ◽  
Key Factors ◽  
Human Influence ◽  
Real Effect ◽  
The Real ◽  
Disturbed Areas ◽  
Predation Rates

The loss and modification of habitats by humans have been considered key factors in the decline of diversity of species worldwide. However, the real effect caused by these disturbances on the biota is still poorly understood. The assessment of the changes in the network of interspecific interactions, such as predation rates on the native fauna, can be an important tool to diagnose the functionality of disturbed ecosystems. In this study we evaluate the predation rate on snakes in coastal grasslands in South America under human influence. Predation rate of artificial snakes, unlike that obtained in other studies, was lower in human-altered areas than preserved ones. Our findings may be due to a reduction in the abundance and/or richness of species of native predators in more disturbed areas.

Effects of early feeding experience and age on the cannibalistic propensity of the land snail Arianta arbustorum

1987 ◽  
Vol 65 (12) ◽  
pp. 3068-3070 ◽  
Author(s):  
Bruno Baur
Keyword(s):  
Land Snail ◽  
Early Feeding ◽  
Vegetable Food ◽  
Egg Cannibalism ◽  
Feeding Experience ◽  
Arianta Arbustorum ◽  
Genetically Determined

The influence of early feeding experience on egg cannibalism was examined in hatchlings of the land snail Arianta arbustorum. The propensity for cannibalism was not affected by cannibalistic or by vegetarian early feeding experience. It was, however, negatively correlated with the age of the snails. Freshly hatched snails with no prior feeding experience chose eggs exclusively, while 16-day-old snails preferred vegetable food. Furthermore, the cannibalistic propensity varied between offspring from different clutches. Restriction of the cannibalistic propensity to the hatchling stage, its nonmodifiability, and differences in its extent between clutches suggest that egg cannibalism in A. arbustorum is a genetically determined trait.

Effect of prey and pollen on interactions between Typhlodromus bagdasarjani and Phytoseiulus persimilis (Acari: Phytoseiidae) on cucumber (Cucurbitaceae)

2017 ◽  
Vol 149 (5) ◽  
pp. 581-591
Author(s):  
Mona Moghadasi ◽  
Hossein Allahyari
Keyword(s):  
Tetranychus Urticae ◽  
Intraguild Predation ◽  
Consumption Rate ◽  
Phytoseiulus Persimilis ◽  
Predation Rate ◽  
Oviposition Rate ◽  
Biocontrol Agents ◽  
Presence And Absence ◽  
Nonsignificant Effect ◽  
Predation Rates

AbstractIntraguild predation is a notable factor to proper application of biocontrol agents to reduce pest populations. Intraguild predation was studied between Typhlodromus bagdasarjani Wainstein and Arutunjan (Acari: Phytoseiidae) and Phytoseiulus persimilis Athias-Henriot (Acari: Phytoseiidae) in presence and absence of Tetranychus urticae Koch (Acari: Tetranychidae) as well as pollen. Intraguild predation between two predators was bidirectional. The highest and the lowest predation rates of both predators in absence and presence of T. urticae as well as in the pollen treatments were on heterospecific eggs and deutonymphs, respectively. Typhlodromus bagdasarjani consumed more heterospecific eggs compared with P. persimilis. When pollen was added, predation of T. bagdasarjani significantly reduced on heterospecific eggs and deutonymphs in absence and presence of T. urticae treatments, respectively. However, predation rate of P. persimilis on heterospecific stages was not significantly affected by pollen addition. Oviposition of both predators was higher in presence of T. urticae than in its absence and oviposition of P. persimilis was significantly higher on heterospecific stages than T. bagdasarjani. Pollen addition had a significant effect on increasing the oviposition rate of T. bagdasarjani. Extraguild prey presence had a nonsignificant effect on the consumption rate of intraguild prey by the intraguild predators. However, presence of extraguild prey led to a significant increase in oviposition rate of both predators.

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