Chapter 3 Evolution Biodiversity and Population Ecology Ecology

Chapter 3 Evolution, Biodiversity, and Population Ecology

Ecology • Ecology and evolution are tightly intertwined • Biosphere = the total of living things on Earth and the areas they inhabit • Community = interacting species that live in the same area • Ecosystem = communities and the nonliving material and forces they interact with

Ecology • Each organism has habitat needs • Habitat = the environment where an organism lives – It includes living and nonliving elements – Availability and quality of habitat are crucial to an organism’s well-being – Human developments conflict with this process • Species survival depends on having suitable habitat

Ecology • Organisms then fill a role in the environment known as a niche • Niche = summary of everything an organism does – Use of resources – Functional role in a community: habitat use, food selection, role in energy and nutrient flow, interactions with other individuals

Ecology Specialists Generalists • species that have narrow niches and specific needs • species with broad niches – Extremely good at what they do – But vulnerable when conditions change – Use a wide array of habitats and resources – Can live in many different places

Population • Population = individuals of a particular species that inhabit an area • Certain characteristics of a population help scientists predict what will happen to them in the future • Population size = number of individuals present at a given time – Populations generally grow when resources are abundant and predators are few – Decline in response to loss of resources, other species, disasters

Population • Population density = the number of individuals in a population per unit area • High densities have advantages and disadvantages – – Easier to find mates Increased competition and vulnerability to predation Increased transmission of diseases Sometimes causes organisms to leave an area if too dense • Low densities provide access to plentiful resources and space but make it harder to find mates

Population characteristics • Population distribution (dispersion) - spatial arrangement of organisms within an area – Random – haphazardly located individuals, with no pattern – Uniform – individuals are evenly spaced due to territoriality – Clumped – arranged according to availability of resources • Most common in nature

Population characteristics • Sex ratio - proportion of males to females – In monogamous species, a 50/50 sex ratio maximizes population growth • Age Structure - the relative numbers of organisms of each age within a population – Age structure diagrams (pyramids) - show the age structure of populations

Birth and death rates • Crude birth/death rates per 1000 individuals • Survivorship curves - the likelihood of death varies with age – Type I: More deaths at older ages – Type II: Equal number of deaths at all ages – Type III: More deaths at young ages

Populations • Natality = births within the population • Mortality = deaths within the population • Immigration = arrival of individuals from outside the population • Emigration = departure of individuals from the population • Births and immigration add individuals; deaths and emigration remove individuals • Crude birth (death) rates = number of births (deaths) per 1000 individuals per year

Populations • Natural rate of population increase = (Crude birth rate) (crude death rate) – Population change due to internal factors • Population growth rate = (Crude birth rate immigration rate) (Crude death rate emigration rate) – Net changes in a population’s size/1000/year • Growth rate as a percent = Population growth rate 100% – Populations of different sizes can be compared

Exponential population growth • Steady growth rates cause exponential population growth – Something increases by a fixed percent – Graphed as a J-shaped curve • Exponential growth cannot be sustained indefinitely – It occurs in nature with a small population and ideal conditions

Limiting factors • Limiting factors = physical, chemical, and biological attributes of the environment that restrain population growth – Space, food, water, mates, shelter, suitable breeding sites, temperature, disease, predators • Carrying capacity = the maximum population size of a species that its environment can sustain • Limiting factors slow and stop exponential growth – An S-shaped logistic growth curve

Influence on population density • Density-dependent factors = limiting factors whose influence is affected by population density – Increased density increases the risk of predation, disease, and competition – Results in the logistic growth curve – Larger populations have stronger effects of limiting factors • Density-independent factors = limiting factors whose influence is not affected by population density – Events such as floods, fires, and landslides

Few logistic grows occur in nature

Ecological Changes • Environments are complex and ever-changing – Limiting factors can change, altering the carrying capacity • Humans lower environmental resistance for themselves – Increases our carrying capacity – Technologies overcome limiting factors • In increasing carrying capacity for humans, we now use immense portions of the planet’s resources – We have reduced the carrying capacity for countless other organisms

Reproductive strategies • Biotic potential = an organism’s capacity to produce offspring • K-selected species = species with long gestation periods, few offspring, and strong parental care – Have a low biotic potential – Stabilize at or near carrying capacity; good competitors • r-selected species = species that reproduce quickly and offer little or no care for offspring – Have a high biotic potential – Populations fluctuate greatly These are the two extremes—most species fall somewhere in between

Conserving Biodiversity • Humans are developing land, extracting resources, and growing as a population – This increases the rate of environmental change for other species • Science can help us understand how we are changing the environment • Impacts threatening biodiversity have complex social, economic, and political roots – We must understand these factors to solve problems

Introduced species • Some introduced species thrive in their new environments, eliminating native species • Native island species are particularly vulnerable – Evolved in isolation with limited need for defenses • Biologists and land managers often must eradicate introduced species to protect native habitats – In Hawaii, pigs are being hunted and pig-free areas are being fenced off

Ecological Changes • Climate change is altering how we protect species and habitats • Land is typically protected to conserve the species that live there – As the climate changes, the protected land may no longer support the same species