ecology exam 3

community

an association of interacting species living in a particular area; also defined as all the organisms living in a particular area

consist of many species, all interacting

•Competition

•Exploitative interactions (e.g., predation, parasitism)

•Mutualism

Etc.

community ecology

: study of how various biotic and abiotic aspects of the environment influence the structure of communities

community structure

includes attributes such as the number of species, the relative abundance of species, and the kinds of species comprising a community

because the study of complete community is extremely difficult, we often use?

subsets of the community

•Taxonomic and/or functional: e.g., plants, mammals, insects

•E.g., Plant Life-form/growth-form

•Combination of structure and growth dynamics (e.g., tree, vine)

Guild

: a group of species, without regard for taxonomic position, that exploit the same class of environmental resource in a similar way

Ant-eating

species

Taxon

A group of phylogenetically related species

Birds

assemblage

phylogenetically related groups within a community

BirdsoftheAmazon

geography and phylogeny

local guild

species that share a common resource and occur in the same community

Ant-eating species of the Amazon

geography and resources

ensembles

phylogenetically bounded groups of species that use a similar set of resources within a community

Ant-eating birds of the Amazon

geography, resources, phylogeny.

species abundance and diversity main takeaway:

Most species in a given community are moderately abundant; few are very abundant or extremely rare.

relative abundance of a species

Relative abundance is the proportion or percentage of a species relative to the total number of all individuals of all species within a community.

absolute abundance of a species

total number of individuals of a species found in a specific study area or community. It is a raw count or an estimate of the actual population size.

what type of distribution does species abundance show

lognormal distribution (bell curve)

many speces have 4 to 32 individuals whereas, only few speces have greater than 64 or less than 2.

better sampling effort shows?

more species abundance distribution

species abundance

number of individuals per species

The relationship between sample size and a species rarefaction curve

As sample size increases, the slope decreases. You begin to repeatedly encounter the most common (dominant) species.

The shape of the curve tells you if your sample size was "enough":

Steep Curve at the end: Your sample size is too small; you are missing many species.

Flat Curve at the end: Your sample size is adequate; you have captured the majority of the biodiversity.

A rarefaction curve

plotting the expected species richness against the number of individuals sampled

species diversity

a measure of diversity that increases with species evenness and species richness

A combination of the number of species and their relative abundance defines species diversity.

species evenness

the relative abundance of species in a community

species richness

the number of species in a community

Shannon Diversity Index

H'= value of Shannon diversity index

pi: the proportion of the ith species

loge: natural logarithm (e=2.718) (aka ln)

S: number of species in the community

Community with only 1 species: proportion = 1

loge(1) = 0 -> H' = 0

H' is always >0

advantages and disadvantages of shannon diversity index

Advantage: H' is simple to calculate Disadvantage: H' is very sensitive to sample size

rank abundance curves

a curve that plots the relative abundance of each species in a community in rank order from the most abundant species to the least abundant species. in a Ln scale.

maximum abundance rank = species richness.

greater evenness = flatter slope

steeper slope indicates animal at the top of the slope dominates over the other species in the community.

Environmental Complexity main takeaway

species diversity is higher in complex environments

increased plant diversity explains?

increased animal diversity

paradox of the plankton Hutchinson 1961

Phytoplankton communities

•Simple environment (open water)

•Competition for same nutrients

•Nitrogen, phosphorous, silica

•Overlapping niches!

niches of algae and terrestrial plants

•Phytoplankton may compete for same nutrients, but have different requirements/abilities to obtain those nutrients

•Recall that the niche is an n-dimensional hypervolume

•Must consider many factors, not just one

variation in soil influences ??

number of communitys.

nutrients enrichment can ?

reduce environmental complexity

•As nutrients increase, diversity of plants and algae declines.

Increasing nutrient availability reduces number of limiting nutrients.

•Light becomes single limiting resource.

•Species most effective at competing for light becomes dominant.

Urbanization Effects on biodiversity

reduces community richness and evenness. decreases diversity

how do we represent feeding relations in a community?

food chain or food web.

food webs

summary of the feeding interactions within a community

reveals community structure.

strong interactions

degree of influence of particular feeding relationship has on community structure.

Direct interactions

interactions between two species (including competition, predation, herbivory, and mutualism) that involve positive or negative effects of one species on another without the involvement of an intermediary species

ex: fox eats rabbit

indirect interactions

one species affects another through a third, intermediary species

ex: bird eats catepiller , caterpiller ate plant. bird poops plant and makes more plants.

indirect interactions: exploitative ( resource ) competition ( negative

indirect interactions Positive

commensalism

An interaction between two species in which one species benefits and the other species is neither harmed nor helped.

indirect commensalism

when the activities of one species indirectly benefit another species without itself being helped or harmed

apparent competition

negative effects as a result of two species sharing a predator or herbivore or as a consequence of one species facilitating populations of a predator or herbivore of a second species

net negative interaction between both preys.

Predator-mediated coexistence

keystone species

species that, dispite low biomass, exert strong effects on the structure of the communites they inhabit.

1. predators might keep prey below carrying capacity

2. if populations are below carrying capacity, less potential for competitve exclusion

3. activity of predatory reduces competitive exclusion leading to increased species richness ( community structure.

ex: sea star removal experiment and otter

dominant species

organisms, such as abundant forest tree species or reef coral species, that substantially influences community structure as a consequence of their abundance

mutualistic keystones

- Mutualists can act as keystone species.•

- Keystone species have high impact on community structure, despite low biomass

ecosystem

a biological community plus all of the abiotic factors

affecting that community

Ecosystem ecologists

include the physical and chemical factors influencing the community and focus on processes such as energy flow and decomposition

photosynthesis converts sunlight into ----?

biomass. convert solar energy into stored energy

Photosynthesis ecosystem scale

•Ecosystems work to absorb,

transform, and store energy

•Physical, chemical, and biological processes

primary production

the production of organic matter, or biomass, by autotrophs in an ecosystem; in most ecosystems, the most significant autotrophs are photosynthetic

rate of primary production

the amount of energy fixed by

the autotrophs in an ecosystem over some interval of time

Gross primary production ( GPP)

the total biomass produced by the primary producers in an ecosystem over some interval of time

Net Primary Production ( NPP)

the amount of biomass left over after autotrophs have met their own energetic needs. NPP is GPP minus respiration by primary producers; it is the amount of energy in the form of biomass available to the consumers in an ecosystem

Trophic levels

•Photosynthetic autotrophs are

Primary Producers

•Herbivores are Primary

Consumers

•Carnivores that eat herbivores are Secondary Consumers

•Etc. (recall food webs)

what causes variation in Net Primary Production?

annual total precipitation and evapotranspiration

Actual evapotranspiration ( temp and precipitation)

Linear relationship.

more evapotranspiration = more primary productivity.

soil fertility and terrestrial primary production

add fertilizer, plants grow. applicable in natural systems

adding N and P increased the NPP by the most.

dry meadow=

N is largely limiting neutrient

wet meadow=

N and P joint limiting

NPP is affected by:

temp, moisture, soil nutirents.

Patterns of aquatic primary production

Aquatic primary production is generally limited by nutrient availability.

Several studies have found a quantitative relationship between phosphorus and phytoplankton biomass

lakes in japan

strong correlation between phosphorous and phytoplankton biomass.

primary producer diversity contributes to higher?

primary production.

•Physical and chemical factors affect rates of primary production.

•Biological factors also influence rates.

plant functional groups

plants with similar physiological and anatomical characteristics.

Manipulated number of species and functional groups that were present in 168 plots.

Plant species richness correlated with primary production.

N-fixing legume and C4 grass functional groups had higher productivity.

plant species richness is correlated with

higher primary production and therefore biomass

primary producer diversity increases

primary production in experimental aquatic systems

•Cardinale (20 11) found increase in nitrate uptake and biomass with increasing algal. species richness.

consumer influences

Consumers can influence rates of primary production in aquatic and terrestrial ecosystems through trophic cascades.

bottom up control

•control of a community or ecosystem by physical or chemical factors such as temperature or nutrient availability

top down control

•the control via influence by consumers

on ecosystem processes

Trophic cascades

actual NPP can be affected by biotic members of the ecosystem

•Effects of predators on prey that alter the abundance, biomass, or productivity of a population, community, or tropic level across more than one link in the food web

top down influence

large mouth bass topic cascade example

•Top down influence, Tropic Cascade

•

•Large mouth bass eat planktivorous fish

•

•Planktivorous fish eat large herbivorous zooplankton

•

•Large herbivorous zooplankton eat phytoplankton

•

•Predation by large mouth bass indirectly reduces the biomass of phytoplankton and NPP

Lake trophic cascade

•Reduction in planktivorous fish populations led to reduced feeding pressure on zooplankton.

•Large-bodied zooplankton soon dominate.

Reduced phytoplankton biomass and rate of primary production

Consistent with reported negative correlation between zooplankton body size and primary production.

compensatory growth

grazing leads to increased growth.

lower plant biomass= lower respiration cost

reducing shading

reduced leaf area= improved water balance.

grazing intensity and compensatory growth

•Too much grazing is obviously not good

•Light grazing is insufficient to produce compensatory growth

•Moderate grazing intensity maximizes

primary production

•Top down control: NPP is affected by the actions of primary consumers

top down control

NPP is affected by the actions of primary consumers

Tropic dynamics

the transfer of energy from one part of an ecosystem.

ecological efficiency

the percentage of energy in the biomass at a lower trophic level that is transferred to the biomass at the next higher trophic level

•Varies from 5%

to 20%

eltonian pyramid

energy is reduced as moving to higher tropic levels

energy transfer between tropic levels is?

inefficient energy is lost.

how much energy is produced in the system =

the amount of tropic levels. higher energy= more tropic levels

energy becomes increasingly limited at

higher tropic levels

the number of trophic levels is limited by

energy availability

energy flow through ecosystems

solar energy ( 100%->) primary producers (1%->) primary consumers (0.004%->) Secondary consumers -> tertiary consumers _>...

energy flows --- ecosystems

through

nutrient cycling

•the use, transformation, movement, and reuse of

nutrients in ecosystems

nutrients include

phosphorous, carbon, nitrogen, potassium, iron, others

nutrient cycles

involve the storage of chemical elements in nutrient pools, or compartments, and flux or transfer of nutrients btwn pools.

the hydrologic cycle pool/ reservoirs vs fluxes

Pools/Reservoirs/Compartments

•Oceans

•Ice

•Groundwater

•Surface freshwater

•Atmosphere

Fluxes

•Evapotranspiration

•Precipitation

•Runoff

Riverflow

nutrient pools

•the amount of a particular nutrient stored in a portion, or compartment, of an ecosystem

•Nutrient cycles are dynamic = fluxes

nutrient flux

•: the movement of nutrients between nutrient pools in an ecosystem

nutrient sink

•part of the ecosystem where nutrient is absorbed faster than released

nutrient source

•part of the ecosystem where nutrient is released

faster than absorbed

Phosporous is critical for

organismal function

•ADP - ATP

•Phospholipids

•DNA, RNA

Calciumphosphate

phosphorous cycle pools

highest to lowest:

Ocean sediments

Soil

Ocean dissolved

Available rock

Organisms

Freshwater

Atmosphere

phosporous cycle fluxes

Dissolved Organisms

Soil Organisms

Runoff

Fertilizer

Marine Detritusè Sediments

Minor atmospheric fluxes

the nitrogen is critcal to

organismal functioning

•Amino acids = proteins

•Nucleic acids = DNA, RNA

•Chlorophyll

•Hemoglobin

•

•Nitrogen is often the limiting factor for plant growth

nitrogen cycle pools

•Atmospheric

•Rocks and sediments

•Ocean

•Soil

•Vegetation

•Marine biota

Nitrogen cycle fluxes

•AtmosphereèOcean

•AtmosphereèTerrestrial

•Terrestrial Cycling

•Marine Cycling

biologically available and unavailable nitrogen

•Atmospheric nitrogen (3.9B teragrams)

•N2 Not biologically available

•N≡N triple bond is very high energy

NH3 is availble to be incorperated into tissues. Plants often via mycorrhizae

animals from plants.

organisms die: bacteria and fungi decompose and release ammonium

nitrogen fixation

•High energy process

•Lightning or nitrogen fixers

•Cyanobacteria

•Free-living soil bacteria

•Nitrogen fixing bacteria at plant roots (legumes)

•Actinomycetes bacteria (plant roots)

Nitrification

•Nitrifying bacteria

•Convert ammonia or ammonium to nitrite and then nitrate

•Chemosynthetic autotrophs

Denitrification

denitrifying bacteria ( often anaerobic conditon)