Deck 7: Energy and Nutrient Relations

Question 1

The introduction to chapter 7 included sketches of the behavior and social systems of several fish species. Using the concepts that you have learned in the chapter, revisit those examples and predict the forms of sexual selection occurring in each species.

Answer 1

Sexual selection is a type of natural selection favoring the elaboration of traits that give advantage to the organism in mating. Sexual selection may be intersexual or intrasexual. In intersexual selection, the member of one sex may select the member of the other sex for mating, depending on a particular trait. In intrasexual selection, there may be competition between the members of the same sex for mating.
The sexual selection has been studied in great detail in guppies. The other fish in which sexual selection can be predicted include the damselfish and the wrasse fish.
Sexual selection in damselfish :
The female damselfish shows mate choice (intersexual selection) by selecting the males holding territories for reproduction and feeding, also assuring offspring fitness. The large male size and the nature of courtship display also have a role in mate choice.
The intrasexual competition is seen in males for acquiring territory. The male also has to defend the territory that acts as a reservoir of food, the site of laying eggs, and rearing of offspring.
Sexual selection in wrasse :
The Wrasse fish is a hermaphrodite and also shows sex change from female to male.
A single male blue head wrasse holds a territory with a collection of females. The intersexual selection or mate choice is dependant on the male coloration and size. The large blue head male wrasse is selected over other males that are small and yellow. The blue head wrasse also shows an attractive courtship behavior.
Intrasexual selection in males is exhibited by competition for fertilization of eggs and maintaining the individual territories. As the bluehead male wrasse extrudes the sperms, the small yellow males in the surroundings extrude a greater number of sperm to fertilize the eggs laid by the females. The additional difference between the bluehead male wrasse and the other yellow males is with respect to the origin. The blue head male wrasse is born as a large female, but changes into the male after the death of the existing blue head male.

Question 2

Suppose that during a field study you find a negative correlation between some variable X and another variable Y-for example, between dry season rainfall and reproduction by green woodhoopoes (see fig. 7.18). Does this negative correlation demonstrate that an increase in X directly causes a decrease in Y?

Answer 2

not answer

Question 3

One of the basic assumptions of the material presented in chapter 7 is that the form of reproduction will exert substantial influence on social interactions within a species. How might interactions differ in populations that reproduce asexually versus ones that engage in sexual reproduction? How might having separate sexes versus hermaphrodites affect the types of social interactions within a population? How should having several forms of one sex, for example, large and small males, influence the diversity of behavioral interactions within the population?

Answer 3

Social interactions between the organisms include the reproductive interactions, cooperative behavior, and competitive behavior.
Reproductive interactions may vary depending on the asexual or sexual mode.
In sexually reproducing populations, the interactions depend on whether the sexes are separate or the species is hermaphrodite. The differences in interactions in asexually and sexually reproducing populations are as follows:
• In separate sexes, the interactions are observed between members of the same sex that leads to intrasexual selection. The interactions between members of the opposite sex lead to intersexual selection. In asexual reproduction, the sex of the individual does not play a role. Hence, there is no intersexual or intrasexual selection observed in asexual reproduction.
• In a sexually reproducing population, competition may exist between the males of the species for acquiring and defending territories providing food, space for mating and raising offspring. The dominant males may show more reproductive success. The reproductive success of males also depends on mate choice or intersexual selection by females. The features considered by females about males include male attractiveness, courtship displays, possession of territories, and quality of offerings. In asexual reproduction, the members are not involved in reproductive interactions. They may however show other interactions such as competition for nutrients, space and water.
Hermaphrodite is the organism with both male and female reproductive organs. Inspite of this, in most cases, they do not self-fertilize. In their population some members may act as males and some as females. They may show social groups that include a single dominant male with a harem of females in a territory.
There may be competition between the males to mate with the females and in defending their territories. Some hermaphrodites may show sex change that ensures availability of a partner for reproduction. Hermaphrodite or bisexual plants may show self-incompatibility and prevent self-pollination. The plant may show nonrandom mating and competition among the pollen donors. Sex change observed in hermaphrodites is not observed in unisexual organisms.
Several forms of one sex may increase the diversity of behavioral interactions in a population. The variations within a single sex of the species may favor intrasexual selection and intra sexual competition. The individual with more desirable features will show high reproductive success. Aggression, acquisition and defense of territories, dominant and subordinate status are dependant on the form of the sex.
Several forms of one sex may give rise to intersexual interactions or mate choice. The attributes possessed by the members of male sex may be judged by the female sex for mating. These attributes of males include body size, attractiveness, courtship displays and aggression.

Question 4

Endler (1980) pointed out that though field observations are consistent with the hypothesis that predators may exert natural selection on guppy coloration, some other factors in the environment could be affecting variation in male color patterns among guppy populations. What other factors, especially physical and chemical factors, might affect male colors and should each influence male color?

Question 5

Endler set up two experiments, one in the greenhouse and one in the field. What were the advantages of the greenhouse experiments? What were the shortcomings of the greenhouse experiments? Endler also set up field experiments along the Aripo River. What were the advantages of the field experiments and what were their shortcomings?

Question 6

Examine figure 7.8. While most of the male guppies that successfully mated were dominant, a substantial proportion of attractive males that sired broods were subordinate. How might we interpret this reproductive success by attractive but subordinate males? What might these results indicate about the potential influence of female choice on mating success among male guppies?

Question 7

Using the studies of Kodric-Brown and Thornhill, compare guppy and scorpionfly mating systems. Pay particular attention to the potential roles of intersexual and intrasexual selection in each species. What are the similarities between the two species? What are some apparent differences?

Question 8

The results of numerous studies indicate nonrandom mating among plants at least under some conditions. These results lead to questions concerning the biological mechanisms that produce these nonrandom matings. How might the maternal plant control or at least influence the paternity of her seeds? What role might competition between pollen determine in the nonrandom patterns observed?

Question 9

The details of experimental design are critical for determining the success or failure of both field and laboratory experiments. Results often depend on some small details. For instance, why did Jennifer Jarvis wait one year after establishing her laboratory colony of naked mole rats before attempting to quantify the behavior of the laboratory population? What might have been the consequence of beginning to quantify the behavior of the colony soon after it was established?

Question 10

Behavioral ecologists have argued that naked mole rats are eusocial. What are the major characteristics of eusociality and which of those characteristics are shared by naked mole rats?

Question 11

Choose a problem in the ecology of social relations, formulate a hypothesis, and design a study to test your hypothesis. Take two approaches. In one approach use field and laboratory experiments to test your ideas. In the second design develop a study that will employ the comparative method.