Biological community:
an assembly of all the population of organisms living close enough together for potential interaction
described by its species composition
Interspecific interactions:
relationship with individuals of other species in the community
greatly affect population structure and dynamics
can be categorized according to their effect on the interacting populations
Interspecific competition:
occurs when populations of two different species compete for the same limited resource
Mutualism- both populations benefit
Predation- one organism kills and eats the other organism
Herbivory- an animal consumes plant parts or algae
Parasitism- the host plants or animals are victimized by parasites or pathogens
Ecological niche- the sum of an organisms’s use of the biotic and abiotic resources in its environment
Interspecific competition occurs when the niches of two populations overlap
Competition lowers the carrying capacity of competing population b/c the resources used by one population aren’t available to the other population
Predication leads to diverse adaptations in prey species like:
camouflage
mechanical defenses
chemical defenses
Herbivores and plants undergo coevolution
Coevolution- a series of reciprocal evolutionary adaptations in two species in which change in one species acts as new selective force on another
Herbivory leads to diverse adaptations in plants
Parasites and pathogens can affect Community composition
Parasite- lives in or in a host from which it obtains nourishment
Pathogens- disease causing microscopic parasite that include
bacteria
viruses
fungi
protists
Non-native pathogens can have rapid and dramatic impacts
Non-native pathogens can cause a decline of the ecosystem
Trophic structure- pattern of feeding relationships within a community
Food chain- the sequence of food transfer up the trophic levels
Producers- autotrophs that support all the other trophic levels
Consumers- heterotrophs
Primary consumers
Tertiary consumers
Quaternary consumers
Detritiviores- get the energy from detritus(the dead material produced at all trophic levels)
Decomposers- have enzymes that digest organic materials and convert them into inorganic forms in the process of decomposition. mainly prokaryotes and fungi
10% rule- only 10% of the energy from one tier gets transferred from one level to the next
Food web- a network of interconnecting food chains
consumers may eat more than one type of producer and several species of consumers may feed on the same species of producer
Species diversity: defined in two components
species richness, the number of species in a community
relative abundance , the proportional representation of a species in a community
Keystone species- a species whose impact on its community is larger than its biomass or abundance indicates and occupies a niche that holds the rest of its community in place
keystone species have a disproportionate impact on diversity
Disturbances: events that damage biological communities. the frequencies and severity may vary from community to community
Communities change drastically following a severe disturbance that:
strips away vegetation
removes significant amount of soil
Ecological succession- results from colonization by variety of species whisch are replaced by a succession of other species
Primary succession- begins in a lifeless area with no soil
Secondary succession- occurs when a disturbance destroys an existing community by leaves the soil intact
Invasive species- organisms that have bben introduced into non-native habitats by human actions
Invaisive species establish themselves at the expense of native communities
The absence of natural enemies → rapid growth of invaisive species
Ecosystem- consists of all the organisms in a community and the abiotic envrionment with the organisms interact
Energy flow- moves through the components of an ecosystem
Chemical cycling- the transfer of materials within the ecosystem
Terrarium- represents the components of an ecosystem and illustrates the fundamentals of energy flow
Primary production:
carried out by producers
the amount of solar energy converted to chemical energy by an ecosystem’s producers for a given area
produces biomass-the amount of living organic material in an ecosystem
Ecosystems vary in their primary production and contribution to the total production of the biosphere
Energy supply limits the length of food chains
Chemicals are cycled between organic matter and abiotic reservoirs
Ecosystems get their energy from:
the sun
the earth’s core
Biogeochemical cycles: include
biotic components
abiotic components
abiotic reservoirs- where a chemical accumulates outside of living organisms
Biogeochemical cycles can be local or global
Carbon cycle
Carbon is found in
the atmosphere
fossil fuels
dissolved in carbon compounds in the ocean
The return of CO2 to the atmosphere by respiration closely balances its removal by photosynthesis
The carbon cycle can be affected by things like:
burning wood
burning fossil fuels
Steps of the Carbon cycle
Carbon enters the atmosphere
Plants absorb CO2
Carbon enters the food chain
Carbon reenters the atmosphere
Sources of carbon to the atmosphere:
burning
decomposition
respiration
Phosphorus cycle
The phosphorus cycle doesn’t have an atmospheric component
Rocks are the only source of phosphorus for ecosystems
Plants absorb phosphorus ions in the soil and build them into organic compounds
Phosphorus are returned ti the soil by decomposers
Phosphorus levels in aquatic ecosystems are typically low enough to be a limiting factor
Nirtogen cycle
nitrogen has 2 abiotic reservoirs
the atmosphere
soil
Nitrogen fixation:
converts N2 compounds of nitrogen that can be used by plants
is carried out by some bacteria
Decomposers- use their enzymes to change the dead living organims into Ammonium by using the process of decomposition
Denitrifiers- converts nitrate and nitrite in the soil into nitrogen gas that enter the atmosphere by using the process of denitrification
Nitrifying bacteria- converts the ammonia into nitrate by using the process of nitification
In aquatic ecosystems, primary production is limited by low levels of:
Phosphorus
Nitrogen
A rapid inflow of nutrients degrades aquatic ecosystems
Over time standing water ecosystems
gradually accumulate nutrients from the decomposition of organic matter
primary production increases in a process known as Eutrophication
Eutrophication depletes oxygen levels and decreases species diversity
Phosphate pollution leading to eutrophication comes from:
fertilizers
pesticides
sewage treatment facilities
runoff of animal waste
feedlots
Although we depend on agricultural ecosystems we also get resources from natural ecosystems
Examples of natural ecosystems:
supply of freshwater and some foods
recycling nutrients
decomposition of waste
regulation of climate and air quality
A rapid increase of food production comes in the expense of natural ecosystems and the resources they produce
Human activities also threaten many ecosystems and their products