Broad geographic patterns in egg and clutch mass are poorly described, and potential causes of variation remain largely unexamined. We describe interspecific variation in avian egg and clutch mass within and among diverse geographic regions and explore hypotheses related to allometry, clutch size, nest predation, adult mortality, and parental care as correlates and possible explanations of vari...

When direct counts are not possible, relative population size indices, based on animal activity (e.g. number of tracks, burrows, feces, calls per unit area), are sometimes the only tools available to investigate population size variations over time. In sea turtles, the number of clutches laid on a nesting beach in a particular season is commonly used as a relative index of population density. T...

How much effort to expend in any one bout of reproduction is among the most important decisions made by an individual that breeds more than once. According to life-history theory, reproduction is costly, and individuals that invest too much in a given reproductive bout pay with reduced reproductive output in the future. Likewise, investing too little does not maximize reproductive potential. Be...

breeding biology of the great cormorants phalacrocorax carbo sinensis is assessed in thesouthern coasts of the caspian sea, iran during the years 2008-2010. about 84 nests located on 63 trees wereexamined. nests were built on large trees located in abbas abad marsh, gilan province. initially, eggs werefound on first week of april and egg laying continued until the last week of may. clutch size ...

Life-history theory predicts that parents produce the number of offspring that maximizes their fitness. In birds, natural selection on parental decisions regarding clutch size may act during egg laying, incubation or nestling phase. To study the fitness consequences of clutch size during the incubation phase, we manipulated the clutch sizes during this phase only in three breeding seasons and m...

Elevated nitrite and microcystin concentrations co-occur during degradation of Microcystis blooms and are toxic to aquatic organisms. We studied the relative and combined effects of these on Daphnia obtusa life-history. Nitrite and microcystin-LR treatments were: 0, 1, 3 mg L(-1) and 0, 10, 100, 300 μg L(-1), respectively. Experiments were factorial with 12 treatment combinations. Incubations w...

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 explai...

Female Nasonia vitripennis lay fewer eggs and increase the proportion of male offspring when ovipositing in previously parasitized hosts compared to unparasitized hosts. This study examines the location and nature of the cues that females use in these clutch size and sex ratio decisions. Neither the sex ratio nor the clutch size response relies on chemical cues on, or a hole drilled in, the out...

analyzed (female curved carapace length, clutch size, emergence success, incubation period, hatchling production, observed clutch frequency, and observed breeding frequency). Although emergence success is lower in hybrids, hatchling production per clutch, as well as clutch frequency and breeding frequency, is similar among the three groups. These results show that hybrids may persist in this re...