Background: The mating system of the korhaans and bustards in southern Africa is either based on polygyny or monogamy. The Red-crested Korhaan(Lophotis ruficrista) has been described as polygynous but otherwise very l...Background: The mating system of the korhaans and bustards in southern Africa is either based on polygyny or monogamy. The Red-crested Korhaan(Lophotis ruficrista) has been described as polygynous but otherwise very little is known about its breeding biology. The aims were to describe the population structure and male behavior during breeding.Methods: The data collected for this paper was mainly based on field transect surveys carried out in 2009, 2010 and 2011. The population structure of the Red-crested Korhaan in the temperate Borakalalo Game Reserve(BGR)was compared with that in the arid Molopo Nature Reserve(MNR)(both situated in the North West province of South Africa). The study was mainly conducted in the BGR but additional work was conducted in the MNR for comparison.Results: The difference in mean group sizes between MNR(1.03) and BGR(1.07) was statistically not significant.Group sizes were not affected by climate despite the fact that the BGR received about 650 mm precipitation per annum and the MNR about 200 mm. In both reserves the apparent sex ratios were skewed in favor of males(1:0.29 in the BGR and 1:0.1 in the MNR). The population was dispersed in a clumped manner which is ascribed to the formation of leks. Leks were positioned in open habitat while females invariably concealed themselves under cover.Conclusions: The leks formed the pivot of the mating system of the Red-crested Korhaan and are identifiable social structures that field ecologists can use to monitor population stability.展开更多
Sex allocation theory applied to hermaphrodites assumes that there is a trade off between the alloca- tion of resources to male and female functions, within a fixed reproductive resource budget. Charnov＇s classic res...Sex allocation theory applied to hermaphrodites assumes that there is a trade off between the alloca- tion of resources to male and female functions, within a fixed reproductive resource budget. Charnov＇s classic resource allocation model predicts a more female-biased sex allocation when competition among different sperm donors is low due to diminishing fitness returns for male investment. By manipulating the social group size, one automatically changes the population density at which individ- uals live. Increasing population density may affect reproductive allocation, leading to resource compe- tition and/or to increased concentration of harmful metabolites. This could lead to an over- or under- estimation of the individual adjustment of sex allocation responses to mating opportunities. In this article, we tested the effects of density and social group size separately on female investment and body growth （considered as proxy of the overall energy budget） in the simultaneously hermaphroditic polychaete worm Ophryotrocha diadema. We manipulated social group size （i.e., monogamous and promiscuous regimes） and density （i.e., 4 levels） using a full-factorial design, to identify the underlying factor affecting female allocation （in terms of egg production） and body growth. In contrast to findings of previous experiments, we found that an increase in population density reduced body growth and egg production of hermaphrodites irrespective of social group size. We advance the hypothesis that the increase of catabolites and oxygen consumption in high-density conditions reduces the overall resource budget and this could obscure group size effects on female fecundity.展开更多
文摘Background: The mating system of the korhaans and bustards in southern Africa is either based on polygyny or monogamy. The Red-crested Korhaan(Lophotis ruficrista) has been described as polygynous but otherwise very little is known about its breeding biology. The aims were to describe the population structure and male behavior during breeding.Methods: The data collected for this paper was mainly based on field transect surveys carried out in 2009, 2010 and 2011. The population structure of the Red-crested Korhaan in the temperate Borakalalo Game Reserve(BGR)was compared with that in the arid Molopo Nature Reserve(MNR)(both situated in the North West province of South Africa). The study was mainly conducted in the BGR but additional work was conducted in the MNR for comparison.Results: The difference in mean group sizes between MNR(1.03) and BGR(1.07) was statistically not significant.Group sizes were not affected by climate despite the fact that the BGR received about 650 mm precipitation per annum and the MNR about 200 mm. In both reserves the apparent sex ratios were skewed in favor of males(1:0.29 in the BGR and 1:0.1 in the MNR). The population was dispersed in a clumped manner which is ascribed to the formation of leks. Leks were positioned in open habitat while females invariably concealed themselves under cover.Conclusions: The leks formed the pivot of the mating system of the Red-crested Korhaan and are identifiable social structures that field ecologists can use to monitor population stability.
文摘Sex allocation theory applied to hermaphrodites assumes that there is a trade off between the alloca- tion of resources to male and female functions, within a fixed reproductive resource budget. Charnov＇s classic resource allocation model predicts a more female-biased sex allocation when competition among different sperm donors is low due to diminishing fitness returns for male investment. By manipulating the social group size, one automatically changes the population density at which individ- uals live. Increasing population density may affect reproductive allocation, leading to resource compe- tition and/or to increased concentration of harmful metabolites. This could lead to an over- or under- estimation of the individual adjustment of sex allocation responses to mating opportunities. In this article, we tested the effects of density and social group size separately on female investment and body growth （considered as proxy of the overall energy budget） in the simultaneously hermaphroditic polychaete worm Ophryotrocha diadema. We manipulated social group size （i.e., monogamous and promiscuous regimes） and density （i.e., 4 levels） using a full-factorial design, to identify the underlying factor affecting female allocation （in terms of egg production） and body growth. In contrast to findings of previous experiments, we found that an increase in population density reduced body growth and egg production of hermaphrodites irrespective of social group size. We advance the hypothesis that the increase of catabolites and oxygen consumption in high-density conditions reduces the overall resource budget and this could obscure group size effects on female fecundity.
