Module 6 Flashcards
(7 cards)
What is the life history of an organism?
Natural selection favors traits that improve an organism’s chance of survival and reproductive success. In every species, there are trade-offs between survival and reproduction, number of offspring, and investment in parental care. Traits that affect an organism’s reproductive and survival make up the life history of an organism. These traits are evolutionary outcomes that reflected in the development, physiology, and behavior. The life-history is the sum of all choices that an organism makes during different phases of its life, choices made by natural selection.
- When reproduction begins
- How often it reproduces
- How many offspring
What is a Darwinian demon?
A Darwinian demon is an iteroparous or semelparous organism that maximizes all elements of its fitness simultaneously. Reproduces directly after birth, maximizes the number of offspring, and lives forever, resulting in unrealistic life history in nature. The closest example may be the r-selected life-history of bacteria.
What are trade-offs and constraints?
Trade-offs can be seen between the number of offspring and the number of resources a parent can devote to each offspring since organisms do not have an unlimited supply of resources. The use of resources for one function – reproduction can reduce the resources needed to support other functions – survival. Trade-offs can also be affected by selective pressures between the number and size and offspring:
If the chance of survival is small Produce many small offspring
High predation rates Many offspring
High degree of parental care Few offspring to increase the fitness
Constraints are divided as:
Internal Genetic and phylogenetic and physiological. The traits noticed in organisms today and the genetic variation in a population that can provide a certain trait in the future. Phylogenetic luggage and genetic potential. Also, the factors that organisms cannot affect, the size of the female pelvis.
External Mechanical, physical, and ecological. Factors that cannot be controlled include the shell of the organism that inhibits growth, or the interaction between other species.
The optimal life-history is the solution that maximizes fitness within the boundaries set by constraints and trade-offs that affect the organism
How do they affect the princple of energy allocation and the cost of reproduction?
The energetic correlation between characteristics – the energy used for survival will affect reproduction and vice versa. It boils down to how an organism uses its energy, and the energy used will be a cost of reproduction since less energy is used for that. The energy can go to collect food, avoiding predators, fighting diseases. For example, a pine tree that releases a high number of cones will have a lower growth.
Optimal clutch size with constraints and trade-offs?
Optimal clutch size is the one that maximizes the fitness of the parents – and the fitness is determined by the number of surviving offspring that they produce. Clutch size in many organisms (e.g. birds) may affect, among other things, survival of both the offspring and the parents. The greater the clutch size, the lower the survival of offspring and/or parents.
Lack: The clutch size is ultimately determined by the average maximum number of young which the parents can successfully raise in the region – evolution has provided a mean clutch size in every species that maximizes the number of surviving offspring from it. Fitness of a parent only depends on the number of offspring from one clutch that survives to adulthood - semelparous
Lacks model consider that the survival of parents is not affected by clutch size.
Williams: Fitness of a parent depends on the number of offspring from a series of clutches that survives to adulthood - iteroparous
What is aging and why does it occur?
Characterized by increased mortality risk and decreased fecundity. Different hypotheses have tried to explain the mechanisms behind aging:
Mutation accumulation hypothesis: Cells carry mutations with increased age and if the amount of problems is correlated to the number of mutations. If there are adverse physiological effects, then the consequences of these effects increase with aging.
Antagonistic pleiotropy hypothesis: Juvenile vigor by positive effects of alleles that later in life will result in senior weakness – a genetic trade-off between traits that affects fitness early in life and the life span.
Those individuals that could reduce the negative effect of aging would have higher fitness and favored by selection. Survival and fecundity at an old age do not affect fitness as much as survival and fecundity at an old age. Thus, the cost of increasing fecundity and survival late in life must be meager to be favored by selection, because the cost cannot be too high.
Evolutionary explanation of aging – A bi-product of life mutations, injuries, wear and tear, etcetera. To fix any of these late in life will only have a marginal effect on fitness.
Clutch size effects?
Depends on if the clutch size has a negative effect on the parents or the offspring. If the clutch size has a negative effect on offsprings or the parents, and is directly correlated to fitness.
They, usually, have different life history r and K selection. As provided by the model of Lack or Williams, the r-selected does not have the same obligations as K, and only reproduce once. To maximize fitness it needs to provide alot many offsprings, and for the iteroparous to recieve the same fitness, it has to have a number that will generate the highest fitness, since it reproduces more than once, to achieve the same fitness. That result in the most optimal number of offspring that do not interfere with the own survival.
