chapter 5Review
In this chapter, we have learned about the biodiversity of Earth, how this biodiversity came to be, and how environmental changes can cause it to decline. The estimated number of species on Earth varies widely, but many scientists agree on approximately 10 million. In any given location, we can quantify the diversity of species in terms of both species richness and species evenness. The diversity that exists came about through the process of evolution. We can view patterns of evolution by placing species on a phylogeny. Evolution occurs when there are changes in the genetic composition of a population. This can happen through artificial selection, natural selection, or random processes. The species that evolve through these processes each have a niche that helps to determine their geographic distributions. Historic changes in the environment have altered species distributions and caused many species to go extinct; current and future environmental changes are expected to have similar effects.
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Module 14 The Biodiversity of Earth
Understand how we estimate the number of species living on Earth.
Scientists have estimated the number of species on Earth by collecting samples of diverse groups of organisms, determining the proportion of all known species, and then extrapolating these numbers to other groups to estimate the total number of species.
Quantify biodiversity.
Biodiversity, can be quantified using a variety of measurements including species richness, species evenness, or both. Such measurements provide scientists with a baseline they can use to determine how much an ecosystem has been affected by a natural or anthropogenic disturbance.
Describe patterns of relatedness among species using a phylogeny.
Patterns of relatedness are depicted as phylogenies. Phylogenies indicate how species are related to one another and the likely steps in evolution that gave rise to current species.
Module 15 How Evolution Creates Biodiversity
Identify the processes that cause genetic diversity.
Every individual has a genotype that, in combination with the environment, determines its phenotype. In a population, genetic diversity is produced by the processes of mutation and recombination.
Explain how evolution can occur through artificial selection.
Evolution by artificial selection occurs when humans select individuals with a particular phenotypic goal in mind. Such selection has produced various breeds of domesticated animals and numerous varieties of crops. It has also produced harmful outcomes, including selection for pesticide-
Explain how evolution can occur through natural selection.
Evolution by natural selection occurs when individuals vary in traits that can be passed on to the next generation and this variation in traits causes different abilities to survive and reproduce in the wild. Natural selection does not target particular traits, but simply favors any trait changes that result in higher survival or reproduction.
Explain how evolution can occur through random processes.
Because evolution is defined as a change in the genetic composition of a population, evolution can also occur when there are mutations within a population or gene flow into or out of a population. It can also occur due to the processes of genetic drift, the bottleneck effect, or the founder effect.
Module 16 Speciation and the Pace of Evolution
Explain the processes of allopatric and sympatric speciation.
Allopatric speciation occurs when a portion of a population experiences geographic isolation from the rest of the population. The composition of isolated populations diverges over time due to random processes or natural selection. Sympatric speciation occurs when one species separates into two species without any geographic isolation. The production of polyploidy individuals is a common mechanism of sympatric speciation.
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Understand the factors that affect the pace of evolution.
Evolution can produce adapted populations more easily when environmental changes are slow rather than rapid. The populations are also more likely to adapt when they have high genetic variation, as is often found in large populations. Should there be a beneficial mutation arise, however, the mutation can spread through small populations more rapidly than large populations. Finally, evolution can occur more rapidly in populations that have shorter generation times.
Module 17 Evolution of Niches and Species Distributions
Explain the difference between a fundamental and a realized niche.
Every species has a range of tolerance to the abiotic conditions of the environment. The conditions under which a species can survive, grow, and reproduce is known as its fundamental niche. The portion of the fundamental niche that a species actually occupies due to biotic interactions, including predation, competition, and disease, is known as the realized niche. Some species are niche generalists whereas other species are niche specialists. The niche a species occupies determines its distribution.
Describe how environmental change can alter species distributions.
Because a species niche represents the environmental conditions under which a species can live, environmental change can cause a change in the distribution of a species.
Discuss how environmental change can cause species extinctions.
When environmental changes are too rapid and too extensive to permit evolutionary changes, or if a species is unable to move to more hospitable environments, a species will not be able to persist and will go extinct.