Ecology Chapters Biology – Campbell Reece

ECOLOGY AND THE BIOSPHERE

Ecology The scientific study of interactions between organisms and the environment ◦ Organismal ◦ Population ◦ Community ◦ Ecosystem ◦ Landscape ◦ Global

Biotic & Abiotic Factors Biotic ◦ Living factors ◦ All the organisms that are part of the individual’s environment ◦ Pathogens, parasites, predators, competitors, food availability Abiotic ◦ Nonliving factors ◦ All the chemical and physical factors ◦ Temperature, light, water, and nutrients

Climate The long-term, prevailing weather conditions in an area Temperature, precipitation, sunlight, and wind Influences the distribution of organisms Global climate patterns are determined primarily by solar energy and planetary movement Local climate patterns are influenced by proximity to water and landscape

Ocean Currents

Sunlight Intensity

Mountains

POPULATION ECOLOGY

Density and Dispersion Population – a group of individuals of the same species living in the same area Density – the number of individuals per unit area or volume ◦ Number of bacteria per milliliter ◦ Affected by emigration and immigration Dispersion – the pattern of spacing ◦ Clumped, uniform, random

Dispersion

Demography and Survivorship Demography – the study of the vital statistics of a population and how they change over time Survivorship curve – a plot of the proportion or numbers of individuals still alive at each age

Change in Population Size Change = (births + immigrants) – (deaths + emigrants) Demographers usually look more at birth and death rate to determine overall population growth ◦ r (rate of increase) = births – deaths ◦ r > 0 the population is growing ◦ r < 0 the population is declining ◦ r = 0 the population is stable (zero population growth)

Exponential Growth A population whose members all have access to abundant food and reproduce at their reproductive potential The population will increase exponentially J-shaped curve

Logistic Growth As population density increases, individuals have less access to resources Carrying capacity (K) – the maximum population that an environment can support S-shaped curve

Life Histories K-selection – populations with high density will have high levels of competition and evolution will favor organisms with low reproductive rate but high survival rate r-selection – populations with low density have low levels of competition and evolution will favor organisms with a high reproductive rate

Limiting Factors Density independent factors – the population is affected regardless of population size/density ◦ Ex. Natural disasters, clear cutting a forest Density dependent factors – the death rate rises or the birth rate falls as density rises A population may change as a result of a combination of the two

Limiting Factors

Density-Dependent Factors Competition for resources Territoriality Disease Predation Toxic wastes

Predator-Prey Predators that rely heavily on a single prey may exhibit a fluctuating population

Human Population Growth

Growth Rate is Decreasing

Demographic Transition Four stages of demographic transition: 1.Both birth & death rates are high, the population grows slowly 2.When health care improves, population size increases 3.Birth rates fall until they roughly equal death rates, population growth slows down and stops 4.Birth rate drops below replacement level, so population begins to decrease

Demographic Transition

Age Structure The distribution of ages in a specific population at a certain time Can be graphed in a population pyramid

Declining Death Rates Death rates have declined mainly because more people have access to adequate food, clean water, safe sewage disposal, and medicines Life expectancy – the average number of years members of a population are likely to live ◦ Most affected by infant mortality

Infant Mortality and Life Expectancy

Global Carrying Capacity ~10-15 billion people ◦ World Population Clock World Population Clock Based on many factors including amount of habitable land, available food (including farmland, average yield of crops, diet) Ecological footprint estimates the amount of land and water area required by each person ◦

COMMUNITY ECOLOGY

Interspecific Interactions Competition Predation Herbivory Symbiosis ◦ Parasitism ◦ Mutualism ◦ Commensalism

Competition Individuals of different species compete for the same limited resources (food, water, shelter, etc.) -/- Competitive exclusion – two species competing for the same resource cannot coexist in the same place ◦ One species will use the resources more efficiently and reproduce more rapidly

Ecological Niche A species use of the biotic and abiotic resources Resource partitioning – use of different niches to avoid competitio n

Predation One species (predator) kills and eat the other (prey) +/- Predators have adaptations to help the catch and kill their prey Prey have adaptations to avoid capture ◦ Cryptic coloration (camouflage), aposematic (warning) coloration, Batesian mimicry, Müllerian mimicry

Defensive Coloration

Herbivory An organism eats parts of a plant or alga +/- Many herbivores have special adaptations to identify whether or not plants toxicity and nutrition Plants use defenses such as toxins or structures (spines, thorns)

Symbiosis Two or more species live in direct contact with each other ◦ May be harmful, helpful, or neutral Parasitism Mutualism Commensalism

Parasitism One organism (parasite) obtains nutrients from another organism (host) which is harmed +/- Endoparasites – live inside the host Ectoparasites – live on the surface of the host Parasites can significantly affect the survival, reproduction, and density of the host species

Mutualism Both species benefit +/+ Obligate mutualism – one species cannot survive without its partner Facultative mutualism – both species can survive alone

Commensalism One species benefits and the other is neither helped nor harmed +/0 Difficult to identify in nature because there may be a slight benefit or slight harm

Species Diversity The variety of different kinds of organisms that make up the community Species richness – the number of different species Relative abundance – the proportion of each species

Trophic Structure Feeding relationships in a community ◦ Autotrophic organisms – primary producers ◦ Herbivores – primary consumers ◦ Carnivores – secondary, tertiary, and quaternary consumers ◦ Decomposers Food chain – transfer of energy from one organism to another Food web – all of the feeding relationships within a community

Food Chains and Webs

Limits on Food Chain Length Energetic hypothesis – food chains are limited by the inefficiency of energy transfer from organism to organism ◦ Only about 10% of the energy is passed to the next trophic level Dynamic stability hypothesis – long food chains are less stable than short chains ◦ Population fluctuations at lower levels are magnified at higher levels ◦ Top predators are most affected

Species with a Large Impact Dominant species – most abundant or have the highest biomass Invasive species – organisms that are introduced into a nonnative habitat Keystone species – has a pivotal ecological niche Foundation species (ecosystem ‘engineers’) – alter the physical environment

Ecological Succession The series of changes that occurs in a community over time Primary succession – occurs in an area where no life previously existed (no soil) ◦ New volcanic island, receding glacier Secondary succession – occurs when an existing community has been cleared by a disturbance (soil is intact) ◦ Fire, hurricane, tornado, human activity

Primary Succession

Secondary Succession