Understanding Bird Evolution Flashcards
In evolutionary terms, what is adaptation?
Adaptation is change (or the process of change) by which a species becomes better suited to its environment—and therefore more likely to survive and reproduce.
Soaring birds like albatrosses and vultures deploy wing-locking structures that allow them to hold their wings outstretched for hours with a little muscle strain.
Which two scientists famously outlined natural selection and “survival of the fittest”?
Charles Darwin and Alfred Russel Wallace in the 1850s.
What is natural selection?
Under the evolutionary process of natural selection, individual birds with advantageous traits tend to have more offspring than individuals without these traits. If these beneficial traits are inherited, the traits will become increasingly common in the population over multiple generations.
What does “fitness” mean when talking about individual birds?
Fitness is the relative success of an individual—compared with other individuals in a population—in passing along their own genes to later generations.
Individual birds with the highest fitness leave the most descendants (survival of the fitness), whereas those with the lowest fitness, leave behind few or no progeny, and their genes become weeded out of the population (death of the least fit).
What is heritability?
Heritability is the proportion of the variation in a (physical) trait that is due to underlying genetic variation.
What are the FOUR basic biological conditions for natural selection to occur?
Natural selection can only occur when:
- Differences exist among individual birds in a population. Because every wild bird is genetically unique, this condition is always met.
2. At least some of this individual variation is heritable so that it can be passed down to future generations.
- Differences exist in the reproductive success of individual birds in a population (how many offspring they can produce).
- Higher reproductive success is associated with heritable differences among individuals. I.e. Fitness relies on heritable traits that help some individuals survive and reproduce better than others.
What does ‘reproductive success’ mean?
Reproductive success is the number of viable offspring produced by an individual over their lifetime.
The more a bird reproduces, the more successful they are in propagating their genes and ensuring the survival of their species.
What TWO characteristics or features are typically heritable due to genes being passed down from one generation to the next?
- Morphological features such as bill size, wing length, and adult body weight. Genetics often accounts for 50 to 90% of the variation of these traits.
- Bird behaviors such as aggression, courtship displays, and food piracy also have a strong heritable component.
What is a lek and give an example of a lekking bird species?
A lek is an aggregation of males that engage in competitive mating displays towards visiting females. The Greater Sage-grouse and New Guinea’s birds-of-paradise are lekking birds.
Male dominance at a lek is associated with longevity. The more energy and endurance an individual has to display, the fitter he likely is, making him the more desirable choice for choosy females.
What is meant by direct fitness?
Direct fitness is the fitness an individual bird gains through its own production of offspring, as measured by it lifetime reproductive success.
What is meant by indirect fitness?
Indirect fitness is the component of an individual’s fitness that results not from their own reproduction, but rather by the aid they give to relatives that then enhance their relative’s reproductive success.
Florida Scrub-jays famously help their parents raise successive generations of babies by bringing them food and defending their territory. While they may never reproduce themselves, they do share genes will the offspring they are helping to raise and, in doing so, are propagating their own genes.
What is Hamilton’s Rule?
Hamilton’s Rule is a formula that describes when an individual should forgo its own reproduction and instead help its relatives reproduce, understanding that the chances of passing on their genetic material is stronger if they work together.
What is artificial selection?
Artificial selection is the evolutionary process analogous to natural selection that results when humans are the selective agent that determines which individuals are allowed to reproduce; often this occurs when humans selectively breed individuals for desirable traits.
The incredible variety of pigeon and chicken breeds we see today is largely a result of artificial selection.
What has driven the evolution of spectacular traits—like fancy plumage—in many male birds?
Sexual selection
What is sexual selection?
Sexual selection is a theory that postulates that the evolution of certain conspicuous physical traits—such as body size, plumage color, or striking adornments—may grant the possessors of these traits greater success in obtaining mates.
These traits are then passed on, which sees subsequent generations sporting more and more extreme forms of these sexually selected adaptations until they become such a hindrance to the male that they negatively impact fitness.
True or false:
Only males develop “fancy” traits through sexual selection.
False.
About 1% of all birds adopt a polyandrous mating system in which females vie for the attention of multiple males and the males, in turn, provide most or all of the post-laying care to the eggs. Consequently, it’s the females that have evolved to be larger and more showy in plumage.
What is meant by reverse sexual dimorphism?
Reverse sexual dimorphism is when the sex that is usually smaller or less ornamented (female) is the larger or more conspicuous sex in a particular species.
Spotted Sandpipers, Red Phalaropes, and the Wattled Jacana are examples of birds that exhibit reverse sexual dimorphism.
Why is it typically the males of bird species that undergo changes due to sexual selection?
One male can fertilize many females who can then lay many eggs and raise many young, which equates to greater reproductive success. Females, however, can only produce a single clutch of eggs after successfully mating. And so it’s typically the males of many species that have evolved to compete for females by perform elaborate songs or mating dances, acquire and defend resources, or boast conspicuous plumage.
What are the two sub-categories of sexual selection?
Intersexual and intrasexual selection
What is intersexual selection?
Intersexual selection involves the reproductive success of individuals that depends on the actions* of the opposite sex.
*Most commonly, the choice of female birds.
What is meant by ‘direct benefits’ when it comes to courtship behaviour?
Direct benefits are the tangible benefits that a mate derives directly from their partner, such as food, access to a good territory, protection from predators, or a high-quality nesting site.
What is courtship feeding?
Courtship feeding is a behaviour in which one member of a pair (usually the male) presents his potential partner with food—a “nuptial gift”—during courtship or before mating.
In the early breeding season, male Northern Shrikes frequently present food items like small birds, voles, and lizards, to females, who are then more inclined to mate with them.
In species exhibiting strong sexual dimorphism, do males contribute to nest-building, egg incubation, or care of the chicks?
Typically no. The males have developed such exaggerated traits so as to attract as many mates as possible and so they contribute nothing more than their sperm to their progeny.
What is the handicap principle?
The handicap principal is based on the idea that when traits are costly to produce and maintain, they are more likely to serve as reliable indicators of individual quality than traits that are easier to produce and maintain. This is why females are attracted to males who have more exaggerated features or behaviors, even though those features might serve as a hindrance. It means they must be strong to survive!
