4.1 Species, communities and ecosystems

Biological species

A group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring.

Population

A group of organisms that interbreed with each other

Difference between species and population

The difference between a species and a population is that a population is a group of organisms of the same species, but they must be living in the same place at the same time. A species are simply two organisms that can interbreed to produce fertile offspring.

Reproductive isolation

The existence of biological barriers that impede members of 2 species from producing viable offspring. Can be before or after fertilization

Prezygotic barriers

Barriers that prevent the reproduction between species

Habitat isolation

When 2 species encounter each rarely or never due to the different habitats they live in.

• Does not have to be isolated by physical barrier. Could be one live in tree another live underground.

Temporal isolation

Species that breed at different times of the day

• Ex: Flower blooms in spring vs another that blooms in summer so cant interchange gametes.

Behavioral isolation

The difference in courtship rituals or behavior that prevent populations from breeding.

Mechanical isolation

Morphological differences that physically prevent mating from occuring

Gametic isolation

The imability of a gamete to fertilize eggs of other species.

Postzygotic barriers

Barriers that reduce the viability or reproductive ability of hybrid offspring.

Reduced hybrid viability

A postzygotic barrier where genes of the different parent species may interact and impair the hybrids development or survival

Hybrid breakdown

A postzygotic barrier when the first generation of hybrids are sterile but the second generation are sterile

Reduced hybrid fertility

A postzygotic barrier where the offspring is sterile even though it is vigorous (strong, able to survive)

• Ex: Mules

Allopatric speciation

When an original population of a species is separated in some ways geographically, causing the gradual creation of a separate species due to geographic isolation

Sympatric speciation

The creation of species when populations are not geograpically isolated. Typically due to factors that change gene flow such as polyploidy, habitat differentiation and sexual selection.

Polyploidy

The presence of extra chromosomes due to errors in cell division. Common in plants.

• The sudden change in the chromosomes can instantly cause changes that create barriers that establishes that strain as a separate species.

Sexual selection

The ability of an individual to attract mates based on their physical characteristics and behaviors.

• Only desirable traits are kept which causes divergent selection which leads to speciation over time

Punctuated equlibrium

The model of the fossil record where there are periods of stagnation followed by sudden changes in evolution.

Gradual change

Evolution of a species with small gradual changes over time

Ecosystem

The community of organisms in an area and the physical factors with which they interact A

Community

A group of populations of different species in an area

Biotic factors

The other organisms that make up the living component in the environment

• Ex: Predation, herbivory, mutualism, parasitism, competition

Abiotic factor

The nonliving chemical and physical attributes of the environment

• Ex: Rock, temperature

• Factors that impact ecosystems are mainly temperature, water and oxygen availability, salinity, sunlight, soil

Autotrophs

Primary producers that build organic molecules from inorganic sources

• Ex: Most plants

Heterotrophs

Organisms that eat other organisms to maintain metabolic function

• Ex: Herbivores and carnivores

Detrivores

Decomposers that feed on nonliving organic matter like dead wood or leaves through internal digestion. Helps with nutrient recycling

• Ex: Worms

Saphotrophs

Decomposers that feed on nonliving organic matter through external digestion

• Ex: Fungi

Water cycle

• Biological importance: Essential to all organisms

• Forms available to life: Primarily liquid, some harvest water vapor

• Reservoirs: 97% of biosphere’s water is in oceans; 2% is in glaciers and polar ice caps; and 1% is in lakes, rivers, and groundwater

• Key processes: Evaporation, transpiration, condensation, precipitation, and movement through surface and groundwater

Carbon cycle

• Biological importance: All organic molecules contain carbon.

• Forms available to life: Photosynthetic organisms convert CO₂ to organic forms used by consumers

• Reservoirs: Fossil fuels, soils, sediments, solutes in oceans, plant and animal biomass, the atmosphere, and sedimentary rocks

• Key processes: Photosynthesis takes up CO₂  and respiration releases it; volcanic activity and burning fossil fuels and wood also release CO₂

Nitrogen cycle

• Biological importance: Amino acids, proteins, and nucleic acids contain nitrogen

• Forms available to life: Plants use ammonium (NH₄⁺) and nitrate (NO₃^-); bacteria use nitrite (NO₂^-); animals use organic forms.

• Reservoirs: Atmosphere (N₂), soils, sediments, surface and groundwater, organisms.

• Key processes: Fixation (N₂ to NH₃), nitrification (NH₄⁺ to NO₃^-), denitrification (NO₃^- to N₂), industrial fertilizers, legume crops, reactive gas emissions.

Phosphorous cycle

• Biological importance: Nucleic acids, phospholipids, and ATP contain phosphorus.

• Forms available to life: phosphate (PO43-) is the most important inorganic form of phosphorus.

• Reservoirs: Sedimentary rocks of marine origin, soil, oceans (dissolved forms), organisms

• Key processes: Weathering of rock, leaching into ground and surface water, incorporation into organic molecules, excretion by animals, and decomposition