EVSC 3200 - Exam Three

What are the biggest agents of change in a community?

Species interactions, abiotic conditions, and disturbances.

Make sure to consider timescale and that abiotic and biotic variables interact with each other!

Abiotic variables that change an ecosystem.

- Temperature, light, water (moisture), soil chemistry, etc.

disturbances

events that injure/kill some individuals and create opportunities for other individuals (ex: tornados, wildfires, floods)

communities cannot form where there are lots of disturbances, can cause succession

intermediate disturbance hypothesis

the greatest species richness can be found at intermediate levels of disturbance

Abiotic agents of change (stress)

abiotic factors that reduce growth, reproduction, or survival of individuals (ex: increasing temperatures)

Biotic variables that change an ecosystem.

- Diseases (cause death or slow growth)

- Species interactions can lead to species replacements

- Ecosystem engineers or keystone species presence

- Invasive species

Pulse disturbances

abrupt disturbance (ex: hurricane)

press disturbances

disturbances that happen gradually over time (ex: prolonged drought, nitrogen loading)

Primary succession

An ecological succession that begins in an area where no biotic community previously existed, very little to no soil, takes 100s of years to millennia

Causes of primary succession

volcano eruptions, exposed rock, melting/retreating glaciers

Order of organisms in primary succession

lichen, moss, grasses, shrubs, coniferous trees, hardwood trees

starts with non-vascular plants + cryptograms (mosses and lichens chemically weather the rock and physical weathering comes after), need to make c-horizon soils before more plants come in

characteristics of early successional species

-good dispersers

-fast growing

- low moisture requirements

- grow and die quickly

- low nutritional requirements

- very stress tolerant

- light-loving, shade intolerant plants

- SOME fix N

characteristics of later successional species

- shade-tolerant, adapted to live in a complex community

- slower growing

- longer lived

"Space for time substitution"

used in biodiversity modeling to infer past or future trajectories of ecological systems from contemporary spatial patterns.

Theories on the predictability of succession - Random/Gleason (FOCUS)

less discrete boundaries between communities, communities are driven by the individual responses of species along environmental gradients, we will see random changes over time

this is the view that is most commonly used

Theories on the predictability of succession - Superorganisms/Clements (FOCUS)

well-integrated groups of species, communities have organismal properties to them, they are repeatable and segregated in space and time (with similar environmental conditions), discrete communities that are tuned into certain elevations w/ abrupt transitions (closed and open communities)

disturbances would eventually heal and go back to the original

Theories on the predictability of succession - Organism and environment interactions/Elton

both organisms and the environment interact to shape succession, each species operates individually with differing rates for succession

characteristics of successional communities

- facilitation --> modifying the habitat in positive ways for other species

- inhibition --> species modify conditions in negative ways to hinder the environment for later species

Ecotones (abrupt)

the divides between groups in a celemencian view of communities

Ecotones (diffuse)

the divides between groups in a gleasonian view of communities

Secondary succession

type of succession that occurs in an area that was only partially destroyed by disturbances, re-establishing the community from a pre-existing one

intense disturbance at any stage can reset the community to a previous stage

How does the presence of soil and life impact succession?

Secondary succession is a lot faster than primary production b/c having pre-existing life makes it easier to continue to grow a community rather than start from scratch

How does a patchy landscape promote species diversity?

uneven disturbance impacts happen all over the landscape, enhances landscape heterogeneity, various ecosystems in various stages of development

Biomagnification

accumulation of pollutants at successive levels of the food chain

Bioaccumulation

An increased concentration of a chemical within an organism over time

Biomagnification vs. Bioaccumulation

Bioaccumulation takes place in a single organism over the span of its life, resulting in a higher concentration in older individuals. Biomagnification takes place as chemicals transfer from lower trophic levels to higher trophic levels within a food web, resulting in a higher concentration in apex predators.

bioaccumulation is in an individual, biomagnification happens over trophic levels

What is species diversity?

The number of different species and the number of individuals of each species within any one community

Consequences of reduced species diversity

lower ecosystem productivity and resilience

How does reduced diversity facilitate disease?

increased levels of host species from loss of other species, infected individuals increase since more hosts = more spread

What shapes diversity?

assembly rules! determined by a number of filters @ differing scales, very complex and also shaped by dispersal, immigration, environmental conditions, and species interactions

Regional species pool

provides an upper limit on the number and types of species that can be present in a community

dispersal and immigration (abiotic filter)

species that can tolerate or require certain environmental conditions in the community pass through the abiotic filter

environmental conditions (biotic filter)

species unrestricted by or dependent on particular species interactions in the community pass through the biotic filter

Native species

species that is found in a certain ecosystem that has evolved to fit in + arrived with no "human intervention" and survived

--> these can be difficult to define sometimes (ex: earthworms + horses)

Invasive species and Introduced Species (non-natives)

newly introduced to a novel environment, NOT ALL INTRODUCED SPECIES ARE INVASIVE

How do humans serve as vectors of dispersal?

- Movement of plants (botanicals and ornamentals)

- Ballast of shipwater

- Wood pallets --> mostly shipping and moving around

- NOT ALL EXOTIC SPECIES BECOME INVASIVE

How do species coexist?

Ecologically similar species can coexist in a community if there are one or more significant differences in their niches

Resource partitioning

Competing species are more likely to coexist if they use resources in different ways (evolved character displacement)

greater overlap = more competition

less overlap = more specialization

how do disturbance and coexistence impact each other?

species can prevent the other from reaching carrying capacity and species can exclude other species, environment depends competition for what

intermediate disturbance impacts on competition

"shifts to peak diversity at lower disturbance frequency/intensity"

- at low levels of disturbance, competition regulates diversity

- at high levels of disturbance, many species cannot survive

dynamic equilibrium model

An elaboration of the intermediate disturbance hypothesis proposing that species diversity is maximized when the level of disturbance and the rate of competitive displacement are roughly equivalent.

intermediate disturbance on positive interactions

facultative interactions tend to shift the curve to the right even higher than intermediate disturbances

community assembly

provides a conceptual foundation for understanding the processes that determine which and how many species live in a particular locality

lottery model of chance

A hypothesis proposing that species diversity in communities is maintained by a "lottery" in which resources made available by the effects of disturbance, stress, or predation are captured at random by recruits from a larger pool of potential colonists.

EMPHASIS ON THE ORDER OF SPECIES SHOWING UP

neutral model of chance

A hypothesis proposing that species diversity in communities is maintained by a "lottery" in which resources made available by the effects of disturbance, stress, or predation are captured at random by recruits from a larger pool of potential colonists.

EMPHASIS ON RANDOM

how does diversity impact ecosystem function?

generally, more diversity is better

diversity stability theory

species richness is positively related to community stability! (the tendency of a community to remain the same in structure and function or to return after a disturbance)

high species richness = high community stability

how does biodiversity and ecosystem function relate?

1) degree of overlap in ecological function between species

2) variation in the strength of ecological functions of the species

niche complementarity

The tendency for coexisting species which occupy a similar position along one niche dimension to differ along another

explain degree of overlap in ecological function of species

do two species do the same function

what are variations in the strength of ecological function

one species is better at a function than another species

complementary hypothesis on species diversity

for every species that you add, you will get a boost in your ecosystem function

idiosyncratic hypothesis on species diversity

for every species that you add, some species may increase productivity, some species may decrease it

redundancy hypothesis on species diversity

when you add some species you get an increase in productivity, but at some point you stop getting an increase (no new contributions to the ecosystem)

what hypothesis describes the saturation of ecosystem function with increasing species richness?

redundancy hypothesis

Species richness

number of different species represented in an ecological community

species evenness

the relative proportion of individuals within the different species in a given area

"Species evenness refers to the extent to which each species is represented in a sample, ranging from dominance by one species (lowest evenness) to equal representation of all species (highest evenness)."

chemosynthesis versus photosynthesis

chemosynthesis uses chemicals to make food (chemical energy), photosynthesis uses light to make food (light energy)

chloroplasts

organelles that capture the energy from sunlight and convert it into chemical energy in a process called photosynthesis

--> evolved from cyanobacterium, have unique DNA than the plant because they evolved differently

what is the role of autotrophs in primary production?

they make the energy! the source of all energy to sustain earth

explain how global CO2 fluxes with primary production (what is responsible for them?)

more PP = less CO^2

less PP = more CO^2 (also includes more CO^2 because increased respiration)

Gross Primary Productivity (GPP)

total amount of carbon fixed by autotrophs in a defined area per unit of time

(NEVER NEGATIVE)

Rate of productivity (PHOTOSYNTHETIC PRODUCTIVITY ONLY)

carbon fixed per area per time

What controls GPP?

1) photosynthesis controls - light, temperature, moisture

2) how much leaf surface/area is photosynthesizing in the plot

Leaf Area Index (LAI)

leaf area per unit of ground area (found by measuring incoming solar radiation

difference between autotrophic and heterotrophic respiration

autotrophic is mostly growth and maintenance

hetertrophic is largely bacteria and fungi

how does climate impact respiration rate?

warmer temperatures = higher respiration

how do you define and calculate NPP (Net Primary Production)

the production we can see!

NPP = GPP - Plant Respiration (Autotrophic Respiration Only)

Always greater than NEP

how do you define and calculate NEP (Net Ecosystem Production)

Net ecosystem production (NEP) is defined as the difference between gross production and total ecosystem respiration, accounting for organic material import and export. It represents the net increment of organic matter within an ecosystem after respiration losses.

o NEP = GPP - Plant/Autotrophic Respiration (AR) and Hetertrophic Respiration (HR)

includes both HR and AR, always less than NPP

daily and seasonal pattern of GPP + NPP

more sun + warmer temps = more GPP

wet + sun = more GPP

what is the daily and seasonal pattern of respiration

colder, less sun = comparatively less photosynthesis

allocation of carbohydrates

the transport of carbohydrates to different places for growth and respiration (transported to a variety of carbon "sinks")

ex: woody biomass for defense, nonstructural carb storage that releases carbon from roots to soil via microbes

what drives allocation

competition and resource availability

more light competition = less NPP is allocated to roots

less nutrient availability = over 50% of NPP is allocated to roots

how are changes in biomass tracked (allometric relationships)

describes how the size of one part of an organism changes in relation to the whole organism

belowground versus aboveground biomass

roots are half the picture...hard to measure because destructive sampling destroys the species

NDVI (normalized difference vegetation index)

A method of measuring the health of vegetation using near-infrared and red energy measurements

remote sensing

The acquisition of data about Earth's surface from a satellite orbiting the planet or other long-distance methods, uses color [red light because chlorophyll] to estimate vegetation with an imagery scale

chlorophyll content can be a proxy for GPP and estimate live plant material

eddy covariance

Finds NEP by measuring fluxes of CO2 going into and out from various heights within a plant canopy [mostly the top]. Also can measure water vapor w/ sensors measuring wind components

Need IRGA [IR gas analyzer]

infrared gas analyzers [how do they work]

emits longwave IR, when it bounces back, measures the greenhouse gases in question

used normally with anemometer that measures wind speed for a more comprehensive measurement (says where air mass is turbulent via rotating eddies)

NEE versus NEP

the signs are different, but they are describing the same thing (+NEP equals carbon sink)

--> NEP is on the exam, NEE is not

what effect does disturbance and human influence have on NEP?

consider time scale! if an ecosystem is destroyed by humans, the NEP goes down.

what are controls on NPP?

light, temperature, water, nutrients, co2

more of these usually results in more NPP (although water does reach a saturation point, anerobic makes the process slow down)

NPP versus Biomass

NPP = the rate @ which material is accumulating

Biomass = standing crop, the snapshot of what you have

what are the trophic levels

1st - primary producers/autotrophs (detritus is here)

2nd - herbivores/detritivores

3rd - carnivores (and omnivores),

allochthonous energy sources

external energy inputs

autochthonous energy sources

internal energy inputs

how and how much energy is lost between trophic levels

90% of the energy is lost between each trophic level (only 10% is passed on)

2nd law of thermodynamics

During any transfer of energy, some is dispersed and becomes unusable --> available energy decreases with each level

trophic pyramids

display the relative energy or biomass at each level

how are terrestrial and aquatic biomass and their energy pyramids different

terrestrial energy and biomass pyramids are similar (similar b/c close associations to energy production), while aquatic biomass is inverted b/c phytoplankton (the primary producers) have a high turnover rate

inverted biomass pyramids are common where productivity is low

plants live long, phytoplankton live short

what affects energy flow

NPP amount at the base of the food web

proportion of each trophic level consumed by the higher level

nutritional content of what is being consumed

efficiency of energy transfers

constraints on energy flow

1) herbivores are constrained by predators and never reach carrying capacity

2) autotrophs have defenses against herbivory like secondary compounds, spines, etc.

trophic efficiency

the energy thats from one trophic level to the other (ex: primary production to secondary consumption)

consumption efficiency (part of trophic efficiency)

the efficiency at which consumers consume primary productivity (eaten or not eaten?), how much of NPP is used [eaten/NPP]

assimilation efficiency (part of trophic efficiency)

once eaten, how much energy is assimilated versus excreted [amount assimilated/amount consumed]

production efficiency (part of trophic efficiency)

what energy is used to grow versus what is respired [amount used to grow/amount assimilated]

how do endotherms and ectotherms have differing energy efficiencies

endotherms use lots of energy to metabolize for heat --> less energy for growth and reproduction (low production efficiency)

ectotherms don't have to do as much metabolism so therefore they use more energy growing and reproducing

how does size of the organism impact the energy efficiency?

higher surface area to volume area = losing heat faster

smaller organisms lose heat a lot faster than big organisms1

trophic cascade

changes in the energy flow in an ecosystem

"bottom-up" control

resources that limit the NPP determine energy flow

consistent effects on each trophic level