Natural Selection?

Question

Under what environmental conditions and habitat types do you think natural selection might favor plants with an annual life cycle?

Answer 1

Environments that vary wildly within a year.  In other words, climates with rough seasons.  Winter is hard times to live in for most plants and animals, so plants have to either shut down and hibernate for the winter, or they simply die out and the seeds wait for spring to start growing.

Answer 2

atural selection acts on an organism's phenotype, or physical characteristics. Phenotype is determined by an organism's genetic make-up (genotype) and the environment in which the organism lives. Often, natural selection acts on specific traits of an individual, and the terms phenotype and genotype are used narrowly to indicate these specific traits.

When different organisms in a population possess different versions of a gene for a certain trait, each of these versions is known as an allele. It is this genetic variation that underlies phenotypic traits. A typical example is that certain combinations of genes for eye color in humans which, for instance, give rise to the phenotype of blue eyes. (On the other hand, when all the organisms in a population share the same allele for a particular trait, and this state is stable over time, the allele is said to be fixed in that population.)

Some traits are governed by only a single gene, but most traits are influenced by the interactions of many genes. A variation in one of the many genes that contributes to a trait may have only a small effect on the phenotype; together, these genes can produce a continuum of possible phenotypic values.[2]

[edit] Nomenclature and usage

The term "natural selection" has slightly different definitions in different contexts. In simple terms, "natural selection" is most often defined to operate on heritable traits, but can sometimes refer to the differential reproductive success of phenotypes regardless of whether those phenotypes are heritable. Natural selection is "blind" in the sense that individuals' level of reproductive success is a function of the phenotype and not of whether or to what extent that phenotype is heritable. Following Darwin's primary usage[1] the term is often used to refer to both the consequence of blind selection and to its mechanisms.[3][4] It is sometimes helpful to explicitly distinguish between selection's mechanisms and its effects; when this distinction is important, scientists define "natural selection" specifically as "those mechanisms that contribute to the selection of individuals that reproduce," without regard to whether the basis of the selection is heritable. This is sometimes referred to as 'phenotypic natural selection.'[5]

Traits that cause greater reproductive success of an organism are said to be selected for whereas those that reduce success are selected against. Selection for a trait may also result in the selection of other correlated traits that do not themselves directly influence fitness. This may occur as a result of pleiotropy or gene linkage.[6]