Exam 3 - Agricultural Ecology Notes

mechanism through which one organism alters the environment to impact another organism

biotic interactions

what are the two type of interferences that create environmental change?

removal and addition

when one organism removes something from the environment or reduces its availability

removal interference

what are the effects of removal interference?

usually negative for one individual

what forms of interaction are considered removal interreferences?

competition, parasitism, herbivory

use or defense of a shared resources, reduces availability, two species occupying similar niches (-,-)

competition

do farmers assume competition in agriculture and if so, how do they deal with it?

yes, they flood the environment with the resources

organisms living in close proximity where parasite derives nourishment from the host but does not kill it (-,+)

parasitism

when plant tissues is removed from the ecosystem (+,±)

herbivory

negative impacts of herbivory

less biomass, less photosynthesis, nutrient removal, decrease in yield

positive impacts of herbivory

stimulate new biomass growth, change species composition

strategic movement of livestock among partitioned pastures

rotational grazing

benefits of rotational grazing (4)

reduced weeds, enhance forage and animal productivity, better nutrient distribution, less compaction/erosion

when are organism adds to the environment and impacts other organisms

addition interference

organism living on the body of another organism, one organism provides habitat for another, no nutritional benefit, form of commensalism

epiphytism

examples of epiphytism talked about in class

algae, moss and ferns, bromeliads and vanilla orchids

when both organisms make additions and both benefit (+,+)

mutualism

degree of specificity of mutualism (2)

facultative and obligate

facultative mutualism

take it or leave it

obligate mutualism

one on one necessary

examples of mutualism talked about in class (3)

pollinators and plants they visit, legume plants and Rhizobia bacteria, plant and mycorrhizae

production of a compound by a plant with an inhibitory or stimulatory effect

allelopathy

combination of a species requirement for every physical and biological resource, includes habitat, nutrition and relationships

ecological niche

most limiting requirement determines growth rate or even presence of the organism

Law of the Minimum

niche requirements overlap, species compete and restrict one another

Competitive Exclusion Principle

all possible conditions in which a species can exist

potential (fundamental) niche

niche that the organism actually occupies due to resource acquisition

actual (realized) niche

_____ partitioning allows organisms to divide up a limiting resources

niche

evolution of a trait in response to competition for a resource

character displacement

change in the trait exhibited in the absence of competition/selection

character release

how are niches used in agriculture?

to determine what plants will grow where

we should intercrop plants with _____ niche requirements

different

competition between different species

interspecific

competition among the same species

intraspecific

what are the positives to decreasing the space between plant rows?

increase plant populations and yield, improved competition vs. weeds

what are the negatives to decreasing the space between plant rows?

difficult passage for equipment, possible increase in plant diseases

ways plant compounds can be released with allelopathy (4)

volatilization, exudation from roots, decomposition, leaching from leaves

allelopathic compounds (4)

tannins, phenolics, terpenes, alkaloids

what are the characteristics of compounds for allelopathy (4)

compounds short lives, may interact with other compounds in environment, differential effect on plants, concentrations vary with plant and conditions

what are the steps to demonstrating allelopathy is occurring? (6)

show compound is released from plant, compound reaches toxic level in environment, uptake by target plant, identify compound and physiological basis for response, understand interaction with environment

what is the negative impact of allelopathy called and what does it do?

inhibitory effect, phytotoxins suppress plant growth

aside from allelopathic plants competing, they can also decrease _____

germination, emergence, growth, soil, symbionts

what are examples of inhibitory allelopathy we talked about in class?

bitter grass with corn, lambs quarter and bean crops

how is allelopathy used for the biological control of weeds? (5)

crop itself, mulch, cover crop, intercropping, crop rotation

what is the positive impact of allelopathy called and what does it do?

stimulatory effect, increase plant growth by pairing with other compounds

what are some examples of stimulatory allelopathy that we talked about in class?

corn cockle and wheat, alfalfa on various crops

predictable changes in species structure and community composition over time

ecological succession

trajectory of succession altered or restarted by ______

disturbance

3 characteristics of disturbance

intensity, frequency, scale

what are some examples of disturbance?

wind, water, temperature, disease epidemics, any agent of change

what agricultural practices are considered disturbances?

tilling (cultivation), planting, harvest, burning

what characterizes the early stages of succession on an agricultural plot (annual weeds)?

rich sources of nutrients, light, harsh and unprotected, not diverse, no vertical structure, early colonizers change environment, life cycle completed in single season, recruitment from the seed bank

what characterizes the first 5 years of succession on an agricultural plot (perennials established)?

multi-year lifecycle, good competitors, out-compete annuals

what characterizes the first 10-15 years of succession on an agricultural plot (pine colonization)?

tree seedlings sprout, shade tolerant species

what characterizes the first 50 years of succession on an agricultural plot?

mature pine forest, hardwood colonization

what characterizes the 100-150 years of succession on an agricultural plot?

oak-hickory forest

where does primary succession occur?

colonization of bare rock, lava flows, glacial retreats, dunes

where does secondary succession occur?

occurs on pre-existing soil following disturbance

what are the characteristics considered for successional species identification? (5)

life history, colonization, dispersal, reproduction, competition

characteristics of colonizers (6)

adapt to extreme environments, wind dispersal, seed bank, low diversity, poor competitors, fast growing, reproduce quickly, semelparous

characteristics of persisters

more restrictive habitat requirements, animals dispersal, high diversity, good competitors, slow growing, reproduce slowly, iteroparous

2 factors that initiate succession?

allogenic and autogenic

what are allogenic factors?

external

what are some examples of allogenic factors?

fire, climate, weather, grazing, human-mediated changes

what are autogenic factors?

caused by organisms in the community

what are some examples of autogenic factors?

facilitation and inhibition

diversity and productivity of natural systems is greatest when moderate disturbance occurs periodically, patchy landscape with multiple successional stages

Intermediate Disturbance Hypothesis

how does modern agriculture deal with succession?

ignores successional process, utilize inputs to replace harvest, rely on early successional stages with high net productivity

how to improve sustainability with succession and agriculture?

less reliance in inputs, utilize later stages of succession

plant or retain trees in crop system

agroforestry

what are the 4 ways populations change size?

birth, death, immigration, emigration

population growth in an unlimited environment where growth continues indefinitely

exponential growth

is the exponential growth model density independent or dependent?

independent

what are the 5 assumptions for an exponential growth population model?

unlimited favorable environment, closed population, continuous growth, no age structure, constant birth and death rates

realistic population growth marked by a carrying capacity and max amount of population an area can hold

logistic growth

is the logistic growth model density independent or dependent?

dependent

carrying capacity

upper limit to population size that an environment will support

if P is very small (near 0) then the growth rate of the population is…

1 or exponential

if P is very large (near K) then the growth rate of the population is…

about 0

what are the added assumptions for the logistic growth model?

constant environment and constant carrying capacity

what happens as a population approaches K?

fluctuates due to time lags

can K change?

yes

how do we impact the carrying capacity in agriculture?

modify environment so crops can increase beyond K

what is the life history strategy used by the following species: colonizer, devotes more energy to reproduction, high rate of increase, responds to disturbance, colonizes favorable situations quickly

r strategists

what is the life history strategy used by the following species: persister, devotes more energy to maintenance, longer life spans in more stable habitats, lower reproductive rates

K strategist

sequence of events in decomposition (4)

organic matter (litter), detritus, humus, inorganic compounds

what directly decomposes plant matter?

bacteria, fungi, actinomycetes, termites

what directly decomposes animal organic matter?

insects and other organisms

what are the 3 domains?

eubacteria, eukaryotes, archaea

what do soil bacteria do?

break down plant OM, mineralize, nitrify, denitrify

what do soil actinomycetes do?

filamentous, mineralize plant OM

what do soil fungi do?

mineralize plant OM, enzymes break down lignin

what dose soil mycorrhizae do?

forms mutualistic relationship with plant roots where fungi provides P and plants provide sugar

what do soil metazoa do?

break down OM into smaller particles, some mineralization

what do soil earthworms do?

eat soil, feed on bacteria and fungi, improve soil structure, increase microbial activity in soil

what do soil termites do?

breakdown wood with high C:N ratio, mineralize plant OM

what do soil millipedes and pill bugs do?

feed on organic matter

what do soil mites do?

fungivores and predators , very diverse

what do soil collembola (arthropod) do?

fungivores with and abdominal appendage

what do enchytraeid worms do?

eat fungi