04.05 Animal Adaptations

Adaptations

Adaptations are changes to the structure of an organism that make it better suited to its environment. For example, as a human being, I don't have any adaptations for surviving day-to-day in the ocean. Swimming is hard without flippers, saltwater burns my eyes, and my skin gets all prune-y and gross. Adaptations begin with genetic variation. Genetic variations are differences in DNA, usually caused by a mutation or a change in DNA. Now, all mutations are not created equal. Other mutations, however, can benefit a species.

Variation

All living things share the same basic genetic code, but the number of chromosomes and the content of the genetic material vary from species to species. Within a species, the genetic material is similar enough that individuals of the same species can breed and produce fertile offspring. But even with that similarity, there are differences. For instance, human beings are all the same species and have 46 chromosomes, but we have a wide array of different characteristics. In the same way, species of other organisms have some natural variation in their genes. Since genes are passed on from one generation to the next, this variety is passed on, too, and mutations add to it.

Artificial selection

Instead of nature selecting which traits are passed on from generation to generation, people make those choices. Sometimes this is done on purpose, maybe to select favorable traits in agricultural plants or animals. Other times, it is an indirect effect of our activities. In the fishing industry, there are rules in place for most species that only fish of a certain size can be kept, and ones that are too small are thrown back.

Overproduction (2)

More organisms must be born than can survive. Overproduction causes competition for resources and survival.

Four things must happen for natural selection to occur

One: More organisms must be born in order for more to survive, you know, so that selection can actually take place. Two: There must be a variation of organisms within a species. Three: Different variations must be inherited, or passed on to offspring. And four: Differences in survival must be due to variation among organisms. In other words, for natural section to occur, the genetic difference must give an organism some sort of advantage in the cutthroat game of survival.

Overproduction

Overproduction of offspring is a driving force in natural selection. All species, even slow reproducers like whales, overproduce in the sense that they have more offspring than can realistically survive based on the resources available. Overproduction has several effects: It increases the likelihood of mutations. The more offspring that are made, the more genetic variation each generation will have, which means spontaneous mutations are more likely to occur. It creates competition for resources. Offspring that are most fit and have traits that help them survive will be the most likely to grow to adulthood and pass on their genes again.

Variation

The characteristics of organisms within a species must vary. These characteristics might help or hurt an organisms chances of surviving.

Descent with modification

The heritable traits that helped an organism survive have been passed on. Over many generations, adaptation could cause a species to evolve.

Directional Selection

The larger fish experienced artificial selection against their body size. The result is that the population's trait distribution shifted toward a smaller body size. This is called directional selection, and it can be caused by either natural or artificial factors. The mean body size of the population has shifted to the left. So how much does body size vary? We can tell by the standard deviation, a measure of how spread out the numbers are. The standard deviation is the square root of the Variance, or how far each fish's body size varies from the mean.

Heritability

Variations must be inherited from one generation to the next. If a certain characteristic helps a species survive, it must be passed on genetically in order to have a long-term effect.

Differential reproduction

When some organisms survive and reproduce more than others due to their variations.

Competition/ intraspecific competition

With genetic variation and overproduction in place, competition takes place both within a species and between species due to limited resources. Competition within the same species is called intraspecific competition. Why competition? Because resources are always limited: there is only so much food, water, and shelter to go around.