CH. 4 Biodiversity and evolution. Core case study: why should we protect sharks?. Sharks have been around for more than 400 million years.. Sharks are a keystone species. People kill about 1.2 million sharks compared to 1 human killed by sharks.
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Biodiversity is a crucial part of the Earths natural capital-
Biological diversity is the variety of the earths species, or varying life-forms, the genes they contain ecosystems in which they live, and the ecosystem processes of energy flow and the nutrient cycling that sustains all life.
Every organism is a member of a certain species with certain distinctive traits.
Biological evolution by natural selection explains how life changes over time-
Most of what we know about past life on Earth comes from fossils.
The fossils so far represent probably 1% of all species that have ever lived.
Biological evolution: the process whereby earths life changes over time through changes in the genetic characteristics of populations.
According to the theory of evolution, all species descend from earlier ancestral species.
Darwin and earth.Wallace described a process called natural selection in which individuals with certain traits are more likely to survive and reproduce under a particular set of environmental conditions than are those without the traits.
Biological evolution through natural selection has become an important scientific theory that generally explains how life has changed over the past 3.5 billion years and why life is so diverse today.
Populations not individuals evolve by becoming genetically different.
The first step of evolution is genetic variability, or variety in the genetic makeup of individuals in a population.
Mutations: random changes in the DNA molecules of a gene in any cell that can be inherited by offspring.
Adaptation: any inheritable trait that improves the ability of an individual organism to survive and to reproduce at a higher rate than other individuals are able to do under prevailing environmental conditions.
2 limitations on adaptation through natural selection.
First, a change in environmental conditions can lead to such an adaptation only for genetic traits already present in a populations gene pool or for traits resulting from mutations, which occur randomly.
Second, even if a beneficial heritable trait is present in a population, the populations ability to adapt may be limited by its reproductive capacity.
“survival of the fittest” means “survival of the strongest”. To biologists fitness is a measure of reproductive success.
organisms develop certain traits because they need them? It just depends on which gene is passed down through more offspring.
Evolution by natural selection involves some grand plan of nature in which species become more adapted? From a scientists standpoint, no plan or goal for genetic perfection has been identified in the evolutionary process.
In the 1960s, Robert MacArthur and Edward O. Wilson began studying communities on islands to discover why large islands have more species.
To explain these differences MacArthur and Wilson carried out research and created the species equilibrium model.
According to this widely accepted scientific theory, the number of different species found on an island is determined by the rate at which new species immigrate to the island and the rate at which species become locally extinct or cease to exist on the island.
Birds are excellent biological indicators because they are found almost everywhere and are affected quickly by environmental changes such as the loss or fragmentation of their habitats and the introduction of chemical pesticides.
Butterflies are also good indicator species because their association with various plant species makes them vulnerable to habitat-loss and fragmentation.
In the 1930s, hunters killed them for their exotic meat and their supple belly skin.
Alligators dig deep depressions, these depressions hold freshwater during dry spells, serve as refuges for aquatic life, and supply freshwater and food for fishes, insects, snakes, turtles, birds, and other animals.
1976, the us government placed the American alligator on the endangered species list, today however today there are well over a million alligators in Florida.
Foundation species play a major role in shaping their communities by creating and enhancing their habitats in ways that benefit their species.
Elephants push over, or uproot trees creating openings in the grassland and woodlands of Africa, this promotes the growth of grasses and other forage plants that benefit small grazing species such as antelopes.
Beavers build dams in streams to create ponds and wetlands that they and other species use.