Ecology: Organization, Factors & Keystone Species

Levels of Organization

• An organism is an individual living thing
• A population is a group of the same species living together
• A community is a group of different species living in a given area
• An ecosystem includes all biotic and abiotic factors in a given area
• A biome is a major regional or global community characterized by climate conditions and plant communities
• The biosphere represents the world

Biotic vs. Abiotic Factors

• Biotic factors are living things that play key roles in an ecosystem
• Abiotic factors are nonliving things that determine which living things can survive in a particular environment

Keystone Species

• A keystone species holds an ecosystem together, similar to how a keystone holds up an arch
• Changes affecting a keystone species can have a ripple effect, causing changes throughout the entire ecosystem

Energy in Ecosystems

• All ecosystems rely on autotrophs for the energy needed for the entire ecosystem
• Most autotrophs require sunlight
• Chemosynthetic autotrophs derive their food from inorganic compounds
• Deep sea vents serve as prime locations for chemosynthetic organisms

Food Chains/Food Webs

• Food chains represent a simple way to view energy flow in an ecosystem by linking feeding relationships
• Trophic levels depict the levels of nourishment in a food chain; energy flows from the lowest to the highest level
• A food web shows the complexities of feeding relationships and energy flows within and beyond a given ecosystem
• Multiple food chains make up a food web

Feeding Strategies and Trophic Levels

• 1st Trophic Level is Producers - P
• 2nd Trophic Level is Primary Consumer - 1º
• 3rd Trophic Level is Secondary Consumer - 2º
• 4th Trophic Level is Tertiary Consumer - 3º

Energy Pyramid

• Most of the energy in an ecosystem is lost as it's transferred between trophic levels
• 90% of energy is lost to the environment as heat
• Only 10% of energy is available to the next trophic level
• Energy pyramids compare the energy used by producers with primary, secondary, and tertiary consumers

Biomagnification/Bioaccumulation

• Biomagnification and bioaccumulation describes the increasing concentration of substances, such as pesticides, in organisms at higher trophic levels in the food chain

Cycles of Matter

• The water cycle demonstrates the circular movement of water, including evaporation, transpiration, condensation, and precipitation
• The carbon cycle involves constant recycling of carbon as key building blocks for organic matter; constantly moving from the environment to organisms and back again
• The nitrogen cycle, where nitrogen is converted into ammonia or nitrate through nitrogen fixation, is essential since organisms can only use nitrogen in specific forms
• The phosphorous cycle is essential for cell development and energy storage molecules such as ATP, DNA, and lipids; insufficient phosphorus leads to decreased crop yields

Climatograms

• Climatograms visually represent average precipitation and temperature of an area

Symbiotic Relationships

• Symbiosis is a close ecological relationship between two or more different species
• Mutualism (+/+) is when both organisms benefit
• Commensalism (+/0) is when one organism benefits and the other is neither helped nor harmed
• Parasitism (+/-) is when one organism benefits and the other is harmed, with the harmed organism being called the host

Competition

• Competition happens when two organisms fight for the limited resources like food, mates, and space.
• Intraspecific competition occurs between the same species
• Interspecific competition occurs between members of different species

Competitive Exclusion

• Two species competing for the same resources can't survive together
• The better species is better for the niche and the inferior will be forced to abandon the niche or go extinct.
• Niche Partitioning involves species utilizing different resources due to competitive advantages
• Evolutionary response involves divergent evolution promoting different physical features

Predation

• Predation is the process when an organism captures and feeds on another
• Herbivores can also be predators
• Predators often have special adaptations such as fangs, claws and venom

Habitat vs. Niche

• A habitat describes the biotic and abiotic factors of the area an organism lives
• Describes where an organism survives
• A niche describes the factors than an organism needs to survive
• Describes how an organism lives

4 Factors that Affect Population Size

• Immigration, the movement of individuals into a population, increases population size
• Births also increase population size
• Emigration, the movement of individuals out of a population, decreases population size
• Deaths decrease population size
• (r) ΔSize = (Births + Immigration) – (Deaths + Emigration)

Growth Rate Formulas

• Birth rate (b) = B/N, where B = births and N = population size
• Death Rate (m) = D/N, where D = deaths and N = population size
• Growth Rate = (B + I) – (D + E), where B = births, I = immigration, D = deaths, and E = emigration
• Growth Rate per capita (r) = b – m, where b = birth rate and m = death rate
• Density = N/Area, where N = population size

Population Density & Distribution

• Population density measures the number of individuals that live in a defined area
• Population density is calculated as the # of individuals/area (units2)
• Population distribution or dispersion describes how individuals within a population are spread out in a given area
• Population distribution can be clumped, uniform, or random

Density-Dependent vs. Density-Independent Limiting Factors

• A limiting factor is a factor that has the greatest effect at keeping the size of a population down
• Density-dependent limiting factors are affected by the number of individuals in a given area and examples include competition, predation, parasitism, and disease
• Density-independent limiting factors are aspects of the environment that can affect a population regardless of its size like unusual weather, natural disasters, and human activities

Exponential vs. Logistic Growth

• Exponential growth happens when resources are abundant and a population size increase very rapidly
• Logistic Growth happens when resources are limited, therefore the population has a slow growth rate until carrying capacity is reached
• Carrying capacity (K) represents the maximum amount of individuals an environment can hold
• A population crash occurs when population decreases rapidly over a short time

Survivorship Curves

• Survivorship curves are generalized diagrams showing the number of surviving population members measured from set of measured set of births
• Survivorship curves help to describe the reproductive strategy of species
• Type I survivorship curves are usually large mammals that provide parental care
• Type II consists of birds, small mammals and reptiles
• Type III consists of inverts, fish, amphibians, and plants

Reproductive Strategies

• r is an unstable environment, density independent
• K is a stable environment, density dependent, interactions
• R have small size, K have large size
• Low energy used to make each individual, High energy for K
• R has many offspring, K has few offspring
• R mature early, K is late with much parental care
• R has short life expectancy, K is long
• R has one time reproductive events, K has more than one
• R is Type III, K is Type I or II

Primary & Secondary Succession

• Succession is the sequence of biotic changes that regenerate a damaged community or create a community in a previously uninhabited area
• Primary succession refers to the establishment and development of an area that was previously uninhabited and examples include lichen or moss
• Secondary succession refers to the reestablishment of a damaged ecosystem in an area where the soil was left intact

Pollution

• Pollution is any undesirable factor added to the air, water, or soil
• Called pollutants, these undesirable factors can directly affect air, water, and soil quality
• Humans are just as important as the other aspects of our biosphere and have just as much of an impact

Air Quality and Pollution

• Smog is a type of pollution that results from interaction of sunlight with fossil fuel emissions
• Smog components include particulates and ground-level ozone
• Acid precipitation occurs when chemicals from fuel emissions enter the water cycle and drop the rainwater's pH

Water Pollution

• Chemical pollutants, raw sewage, trash and other waste products biggest threat to aquatic ecosystems
• Indicator species are used to determine the health of the ecosystem because they show direct effects of pollution
• Biomagnification happens when a pollutant moves up a food chain and increases concentrations in the predators

Rising Atmospheric CO₂

• As human populations rise, more energy and food are required
• The increase in fossil fuel burning and deforestation leads to human derived sources of atmospheric carbon dioxide

The Greenhouse Effect

• Some sunlight is absorbed by the earth's atmosphere while the rest gets reflected off of the earth's surface
• Some light gets trapped by greenhouse gases
• Water vapor, methane, and carbon dioxide are the major greenhouse gases

Global Warming

• An increase in greenhouse gases causes more heat to be trapped, thus increasing planet temperature
• A global warming disagreement exists about human impact but evidence does point to an increase in temperatures
• Effects on planet are unknown but potentially drastic

Ozone Depletion

• Ozone is found in the stratosphere
• Ozone protects us from UV radiation
• Gases, known as CFCs (chlorofluorocarbons), break ozone down
• CFCs are found in aerosols and refrigerants

Effects of human growth on environment

• Humans consume a majority of nonrenewable resources such as oil and coal
• However, humans are finding new resources to replace these such as wind

Threats to Biodiversity

• Habitat Loss/Destruction
• Invasive/Introduced Species
• Population Growth (Human)
• Pollution
• Climate Change
• Overexploitation