Geographic Variation In Clutch Size Research Articles

Geographic Variation in Clutch Size and Reproductive Season of the Dwarf Caiman,Paleosuchus palpebrosus,in Brazil

Abstract We studied nesting of Cuvier's Dwarf Caiman, Paleosuchus palpebrosus, in flooded forest around the Amazon River, and streams draining into the Brazilian Pantanal. Nests were located by searching on foot. Eighty nests were located in the Amazonian sites between 2001 and 2010, and 35 nests were found in the Serra das Araras Ecological Station and streams draining Urucum Mountain on the periphery of the Pantanal between 2006 and 2011. Sizes of embryos indicated that nesting occurs in the Amazonian sites during the dry season and coincides with falling water levels. Although nesting coincides with the warmest and wettest months in the streams around the Pantanal, the streams are not subject to long-term floods. Clutch size varied from eight to 21 eggs, was correlated with female size, and the mean clutch size did not differ between the Amazonian sites and those around the Pantanal.

Breeding ecology of the Chestnut-backed Sparrowlark Eremopterix leucotis in an agroecosystem in the Limpopo province, South Africa

We studied the breeding ecology of the Chestnut-backed Sparrowlark Eremopterix leucotis over three years between 2008 and 2010. The breeding season was bimodal with a main peak in laying in autumn (March–April) and another smaller peak in spring (September–October). Nest microhabitat analyses showed they prefer nesting in open areas with lots of bare ground (median 67.5%). Nest entrance directions were biased towards the south (mean vector (µ) = 186.44°). The majority of nests (78.2%) had an apron at the nest entrance. The mean clutch size was 1.88 but there was geographic variation in clutch size between northern and southern races of the species. The mean incubation and nestling periods were 10.33 d (range 10–11 d) and 9.20 d (range 8–10 d), respectively. The results suggest that parental contributions during incubation are almost equal, but females made significantly more food deliveries during the nestling period compared to males. The diet of nestlings comprised mainly of invertebrates (50.2%), seeds (34.4%) and unidentified food items (15.4%). Breeding success was low, averaging 16.1% (range 8.1–20.6%), and the average number of fledged young per pair was 0.36 ± 0.71. Replacement broods were common and we also recorded repeat brooding attempts.

Geographic variation in calcium and clutch size

For over a half century numerous hypotheses have surfaced aimed at explaining a key life history trait, the evolution of clutch size in birds. A principal goal has been to explain why clutch size generally increases with latitude both within species and among closely related species. Most hypotheses have stressed food limitation, predation, or seasonality. I present a novel hypothesis to explain geographic variation: a limitation of calcium resulting from broad scale variation in this element. Because the storage capacity of avian medullary bone is limited or nonexistent, during egg formation, female birds must intake supplemental calcium. Yet calcium and other exchangeable bases are much rarer in tropical soils. I briefly review the abundant experimental and observational evidence supporting how calcium limitation affects clutch size and other life history traits, and I present a series of predictions (and apparent support for them), stemming from the calcium variation and limitation hypothesis. The balance of evidence suggests that variability in availability of environmental calcium plays a proximate and ultimate role in the evolution of clutch size. Although this hypothesis is not mutually exclusive with others, it highlights another factor that needs to be considered in studies of the geographic variation in clutch size.

Investigating geographic variation in clutch size using a natural experiment

Summary Clutch sizes generally increase with latitude, and are smaller at southern latitudes compared with equivalent northern ones. Descriptions of such patterns and attempts to identify their causal mechanisms are complicated as different species, with different ecological traits are often compared in different regions. We reduce such problems by using the introduction of 11 passerine species from the UK to New Zealand as a natural experiment to explore interspecific geographical variation in clutch size. Nine species have significantly smaller clutches in New Zealand than the UK. Seasonality, measured both by climate and how birds respond to variation in resource availability, is also lower in New Zealand. Comparing across species, the magnitude of clutch size change is unrelated to the magnitude of reduced seasonality that each species experiences. Such observations are partly compatible with Ashmole's hypothesis that areas with high seasonality have large clutch sizes (higher winter mortality results in a breeding population that is significantly lower than the environment's carrying capacity, and hence in extra resources for rearing chicks). However, additional data on seasonal changes in resource availability and population densities, combined with comparative data on survival and nest predation rates, are required to evaluate fully the mechanisms generating smaller clutches in the southern hemisphere. We discuss the potential determinants of geographical variation in the patterns of temporal variation in clutch size.

GEOGRAPHIC VARIATION IN CLUTCH SIZE AND A REALIZED BENEFIT OF AGGREGATIVE FEEDING

We investigated one causal explanation for geographic variation in clutch size and aggregative feeding of the pipevine swallowtail, Battus philenor. Populations in California lay larger clutches than those in Texas, and larger feeding aggregations grow at an accelerated rate on the California host plant. Using reciprocal transplant experiments with larvae from California and Texas populations, we found that the benefit of increased growth rate associated with feeding in larger groups occurred only on the California host plant and was observed for larvae from both populations. These results are consistent with the hypothesis that larger clutch size and aggregative feeding are adaptations to characteristics of the California host plant. Future studies on the evolution of clutch size and aggregative feeding of herbivorous insects should consider how these life-history traits affect host plant suitability.

GEOGRAPHIC VARIATION IN CLUTCH SIZE AND A REALIZED BENEFIT OF AGGREGATIVE FEEDING

We investigated one causal explanation for geographic variation in clutch size and aggregative feeding of the pipevine swallowtail, Battus philenor. Populations in California lay larger clutches than those in Texas, and larger feeding aggregations grow at an accelerated rate on the California host plant. Using reciprocal transplant experiments with larvae from California and Texas populations, we found that the benefit of increased growth rate associated with feeding in larger groups occurred only on the California host plant and was observed for larvae from both populations. These results are consistent with the hypothesis that larger clutch size and aggregative feeding are adaptations to characteristics of the California host plant. Future studies on the evolution of clutch size and aggregative feeding of herbivorous insects should consider how these life-history traits affect host plant suitability.

On clutch size and hatching success of the South American turtles Podocnemis expansa (Schweigger, 1812) and P. unifilis Troschel, 1848 (Testudines, Podocnemididae).

Data on clutch size and hatching success of P. expansa were gathered for seven beaches traditionally used by the species and re-analyzed statistically by means of regression analysis, of the number of eggs on the number of females (or nests) and of the number of young on the number of eggs. All regressions were linear, passed through the origin and had excellent fits. Average clutch size varied from 75 to 123, and presented geographic differentiation: (i) Rio Orinoco, (ii) Rio Trombetas + Rio Branco and (iii) Rio Juruá + Rio Purus. Average hatching success was ca. 83%. In P. unifilis there was also geographic variation in clutch size, the Iquitos area showing the highest values. Hatching success of P. unifilis was uniformly high: only one sample, from Iquitos, had less than 90% success. The outstanding fit of the clutch size regressions leads one to consider egg volume variability, which was found to be high in both species, in contradiction with current optimal egg size theory.

Variation in Clutch Size and Ovum Size of the Snubnose Darter, Etheostoma simoterum (Cope), from Two Populations in Tennessee

Abstract I studied variation in clutch size and ovum size of the snubnose darter Etheostoma simoterum from three sites in Bluewater Creek in southern Tennessee which I compared to published data for a population from Brush Creek in northern Tennessee. Females 29–44 mm standard length (SL) from Bluewater Creek (n = 54) produced 25–96 (x = 63) eggs per clutch. SL-adjusted clutch sizes varied among the localities within Bluewater Creek with the largest mean clutch size being 1.14 times greater than the smallest. Mean diameter of unovulated ripe eggs in individual females ranged from 1.15–1.34 mm (x = 1.24 mm diam) and mean egg mass ranged from 251–380 (x = 312) μg. Both metrics showed significant correlations with SL. Females from Brush Creek produced significantly larger SL-adjusted clutches than females from Bluewater Creek, but egg diameters did not differ significantly between populations. Comparison of the two populations shows interesting geographic variation in clutch size that may result from raci...

Geographic and Ecological Variation in Clutch Size of Tree Swallows

AbstractIn many birds, populations breeding at higher latitudes have larger clutch sizes. It has been hypothesized that this relationship results from the greater availability of food at higher latitudes. We examined geographic variation in clutch size of Tree Swallows (Tachycineta bicolor) in relation to latitude, longitude, laying date, breeding density, elevation, and summer actual evapotranspiration (AE). AE is a measure of terrestrial primary productivity, and we assumed that it was correlated with resource abundance. Clutch size data were compiled from nest records throughout the breeding range in the United States and Canada (n = 7,459). Summer AE estimates were made from long-term climatological records, and breeding density was estimated from Breeding Bird Surveys. All variables were averaged for each 1° block of latitude and longitude (n = 85 latilong blocks). We found a strong positive relationship between clutch size and latitude. Absolute levels of resource abundance (summer AE) were not related to clutch size but were related inversely to latitude and longitude. After controlling for the effects of confounding variables, clutch size was related positively to latitude and relative resource abundance (summer AE after controlling for breeding density). Our results are consistent with Ashmole's hypothesis that relative, rather than absolute, levels of resource abundance determine at least some of the variation in clutch size.

GEOGRAPHIC AND ECOLOGICAL VARIATION IN CLUTCH SIZE OF TREE SWALLOWS

Abstract In many birds, populations breeding at higher latitudes have larger clutch sizes. It has been hypothesized that this relationship results from the greater availability of food at higher latitudes. We examined geographic variation in clutch size of Tree Swallows (Tachycineta bicolor) in relation to latitude, longitude, laying date, breeding density, elevation, and summer actual evapotranspiration (AE). AE is a measure of terrestrial primary productivity, and we assumed that it was correlated with resource abundance. Clutch size data were compiled from nest records throughout the breeding range in the United States and Canada (n = 7,459). Summer AE estimates were made from long-term climatological records, and breeding density was estimated from Breeding Bird Surveys. All variables were averaged for each 1° block of latitude and longitude (n = 85 latilong blocks). We found a strong positive relationship between clutch size and latitude. Absolute levels of resource abundance (summer AE) were not rel...

The relationship between geographic variation in clutch size and migration pattern in the Yellow Wagtail

Clutch size in the Yellow Wagtail increases by about one egg per 19° of latitude throughout Europe, but at a given latitude larger clutches are laid in western than in eastern Europe. In eastern Asia there is evidence of a reverse latitudinal cline, in which clutch size is smaller at higher latitudes, and considerably smaller than in Europe at equivalent latitudes. These trends suggest that smaller clutches are laid by populations with access to extensive wintering areas in east Africa and south-east Asia, whereas larger clutches are laid by populations with more restricted wintering areas in west Africa and India. Higher winter mortality in the latter populations may reduce breeding density, leading to less competition for resources and allowing larger clutches to be produced.

Geographic Variation in Clutch Size in the Northern Flicker (Colaptes auratus): Support for Ashmole's Hypothesis

AbstractThe Northern Flicker (Colaptes auratus), a common hole-nesting North American woodpecker, exhibits a highly significant latitudinal increase in clutch size. Using preserved clutches and information on climatic conditions and breeding densities of confamilial species, I examined the hypothesis that this geographic trend is the result of seasonal fluctuations in resources ("Ashmole's hypothesis"; Ashmole 1961, 1963; Ricklefs 1980). Clutch size is significantly correlated both with the ratio of summer productivity to estimated breeding densities of all woodpecker species and with the ratio of summer to winter productivity, supporting Ashmole's hypothesis. In addition, a substantial portion of the latitudinal gradient can be directly explained by the seasonality of resources, primarily because of an inverse correlation between clutch size and winter productivity. These results provide the first corroboration of Ashmole's hypothesis from an examination of intraspecific clutch-size variation and suggest that geographic trends in fecundity in some cases may be largely attributable to trends in seasonal fluctuations of resources.

The Evolution of Egg Clustering by Butterflies and Other Insects

On met en evidence le fait que la ponte en grappes chez de nombreux lepidopteres (et d'autres insectes) a evolue en reponse a la selection pour une fecondite accrue