Unit 4: Biodiversity and Endangered Species Section 1: Evolution and Biodiversity

Central Case Study: Saving Hawaii’s Native Forest Birds  Due to its isolated location, Hawai’i has been a location for dramatic evolution over the millennia  Common ancestral bird arrived in the islands millions of years ago  Birds evolved, without any predators, to be specialists (small niche)  Europeans arrived and brought many species (pigs, cattle, rats, dogs, mongoose, etc.) which destroyed the native birds’ habitats and killed their young/eggs  Avian malaria also had major impact on demise of Native birds  Only ½ of the original species remain in Hawai’i

Humans have not been on Earth very long…

How can we tell which organisms lived in the past?  Fossil records allow us to observe the physical and chemical conditions of past time periods in the earth’s existence  Fossils have shown:  Life has existed for about 3.6 billion years on Earth  The number of species living at any one time has increased over time  The species living today are a small fraction of the species that have ever lived here  There have been several mass extinctions where large numbers of species died simultaneously

Earth has undergone several different mass extinctions Tertiary Bar width represents relative number of living species EraPeriod Species and families experiencing mass extinction Millions of years ago Ordovician: 50% of animal families; Cause: Unknown Devonian: 30% of animal families; Cause: Unknown Cambrian Ordovician Silurian Devonian Extinction Paleozoic Mesozoic Cenozoic Triassic: 20% of families; 50% of genera; Cause: Unknown Permian: 80-95% of all species; Cause: Possible volcanism Carboniferous Permian Current extinction crisis caused by human activities. Cretaceous: >50% of species up to 80% of ruling reptiles (dinosaurs); Cause: likely asteroid impact Extinction Triassic Jurassic Cretaceous Extinction QuaternaryToday

Biological Evolution  Change in a population over time  Changes in genetics leads to changes in appearance, function, or behavior within a species  Natural selection leads to variation of genes in a population because those characteristics that enhance survival or reproduction (adaptive traits) are passed down to successive generations  Proposed in 1858 independently by Charles Darwin and Alfred Russel Wallace  Darwin – Galapagos Islands; Wallace – Malaysia

Types of Evolution

Anthropogenic Effects on Evolution  Humans have a huge impact on evolution in certain species.  Humans select the best/most desirable organisms from a species and selectively breed them  This gives rise to many of the pets and foods that we live with today

Biodiversity  Whether it be natural (adaptation or mutations) or anthropogenic (artificial selection), variation leads to diversity or organisms  Separated into three categories:  Ecosystem diversity  Species diversity  Genetic diversity

Types of Biodiversity  Ecosystem Diversity: Describes the diversity of ecosystems or types of habitats in an area  Species Diversity: Describes the variety of species in an area  Species richness – used to determine the number of species in an area  Evenness (Relative Abundance) – describes how the populations of species relate to one another in terms of size  Genetic Diversity: Relates to the differences in the DNA of individuals in a species  Populations with high genetic diversity can usually cope well with environmental change

Species on Earth  As organisms converged from a common ancestor, they diversified  This process of developing new species is called speciation  New species arise due to geographic barriers (allopatric speciation)  Species can also diverge because of mutations within a population that is not geographically separated (sympatric speciation)  Species have not become evenly distributed among the taxonomic groups (total 1.8 million species)  Insects encompass over 73% of all animal species on the planet  Among the insects, over 40% are beetles

Species are not evenly distributed taxonomically

Species are not evenly distributed geographically  The species richness of ecosystems is higher closer to the equator (latitudinal gradient)  Reasons for this:  High plant productivity to support animals  Stable climate allows specialization and resource partitioning  No recent historical glaciation so no species have had to leave in recent geologic history

Species richness increases towards the equator