Chapter 37 Communities and Ecosystems

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

1. Primary consumers

2. Tertiary consumers

3. 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

1. species richness, the number of species in a community

2. 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

1. Carbon enters the atmosphere

2. Plants absorb CO2

3. Carbon enters the food chain

4. 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

1. the atmosphere

2. 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