PCB 3044 Exam 3

Chapter 12: Predation

Hudson Bay Co. Trade

Allows us to track population cycles of snowshoe hares

What causes population cycles in hare and lynx?

-FOOD supplies become limiting when hare population density is high

- PREDATION by lynx and other predators can explain drop in survival rates

Predation

a trophic interaction where individuals of one species (a predator) benefits by consuming individuals of another species (its prey).

Parasitoids

insects that lay eggs within another host, after hatching the larvae stay in the host which they eventually kill and eat

Predators generally focus on areas that

yield abundant prey

(Some predators are sit and wait, while others relocate to areas with abundant prey)

Generalist Predators

Most Predators are often generalists and consume whatever is available

Specialist Predators

show a preference in what they eat regardless of abundance

(ex. Hare constitute 20% of lynx available food, yet make-up 60-80% of their diet)

Search image:

the heightened ability of a predator to detect a target

(Animals will gain experience with specific species of prey to become more efficient at capturing them

This will lead the predator to focus on that species and ignore other prey)

Herbivores eat

they are mostly specialists and eat specific parts of plants

(Leaves are the most consumed part; other than seeds because of their abundance and nutrition)

Nitrogen content from greatest to least

-animals

-seeds

-angiosperm leaves

-gymnosperm leaves

-phloem sap

-xylem sap

Herbivores reduce what?

Herbivores reduce the growth, survival, and reproduction of plants

(Seed consumption limits reproductive success

Growth is reduced after herbivory (eating)of roots)

Narrow range

Herbivores feed on a narrow range of plants.

(grass hoppers feed on a wide range)

How do predators forage for food?

some search through their habitat (wolves)

some sit and wait for prey to enter their striking zone(sessile, like carnivorous plants)

For any prey defense mechanism

there is usually a predator with a countervailing offense

Many predator have physical features

for prey capture

(snake skull bones aren't rigid so they can eat bigger things than their heads)

Poison and mimicry

Some predators use poison to subdue prey (venomous spiders), others use mimicry to blend into their surroundings

Tolerate chemicals

Other predators can tolerate or detoxify chemicals from the prey (Garter snakes can eat toxic newts, but they move slower and are stationary for 7 hour after eating them)(they have an evolved resistance to the toxin)

Prey defenses (to escape being eaten by predators)

large size (elephants)

rapid movement (gazelles)

body armor (snails, armadillo)

Coloration defense mechanisms used by prey

Aposematic- warns predators not to eat toxic organisms (based on bright colors)

Crypsis- helps prey resemble their background and blend in (camouflage)

False advertising- coloring that resembles other toxic/ dangerous organisms (but the animal itself isn't toxic)

Mimicry defense mechanism

when prey resembles another fierce organism or the environment

Batesian- 1 species mimics a different harmful species

Mullerian- both species are harmful

Prey alter their behavior

by avoiding open area

keeping a lookout

and forming defensive circles

Some prey have chemical

repellents that are toxic or irritating, with varying levels of accuracy

-All adaptations have trade offs

(ex. Of 4 snail species eaten by shore crabs, the species with the thinnest shell takes refuge most quickly. Snails with thickest shells are the last to take refuge.)

Some plant responses to herbivory

Masting- some plants produce lots of seeds, with other years producing hardly any

Compensation- growth response to herbivory where the removal of tissue stimulates new growth

Full compensation- herbivory causes no net loss of the plant tissue

Herbivory early in the growing season will lead to compensation but later in the season it won't

Many plants have structural defenses

Such as thick leaves, spines/ thorns, sharp edges, and piercing hairs.

Induced defenses- a result from a herbivory attack ( cacti growing spikes to ward off herbivores)

(Secondary compounds—toxic chemicals to reduce herbivory directly)

Secondary compounds

make plants taste bad, or the opposite where it attracts the herbivore ( Some are produced all the time while others aren't)

Some herbivores can overcome

Some herbivores can overcome plant defenses through digestive enzymes or behavior

Lokta- Volterra model

Lokta- Volterra model- displays predator/prey relationships

-Predators is 0= prey population grows exponentially

-Predators present= rate of prey capture depends on frequency/ efficiency of capture

-No prey= predators starve

-Prey are present = individuals are added to the predator population depending on the number of prey killed and efficiency of predators

Model suggests that predator-prey interactions are inherently cyclic (the decrease in predator population is followed by an increase, and this happens over and over again)

Population cycles are difficult to recreate in a lab

they lack the dynamics of natural environments

(If prey are too easy to find, predators usually drive them to extinction)

Huffaker's experiments

Predatory mite eats herbivorous six-spotted mite (eats oranges);both populations went extinct

(predators ate the mite and orange and they both went extinct)

A variety of factors can prevent predators from driving prey to extinction

Some of the factors include habitat complexity, dispersal, prey switching, spatial refuges (where predators cannot hunt effectively/prey can hide from predators), and evolutionary changes

Predators and herbivores can change

the outcome of competition which affects distribution and abundance (If a predator or herbivore decreases performance of the top competitor, it may indirectly enable an inferior competitor to increase in abundance.)

Predators can reduce

the density of prey species and change nutrient dynamics

(Affect nutrient inputs in the environment and change the ecosystem)

(ex. Arctic foxes were introduced to some AleutianIslands ~1900. Reduced seabird density by ~100X lowered nutrient input; shift from grasses to shrubs)

These interactions may affect the physical environment

If an animal preys on aquatic plants that serve as filterers, water can shift from clear water to turbid (cloudy) water

(Golden apple snails introduction to Taiwan cause a shift from clear water to turbid)

Chapter 14 Competition

Competition

Darwin

was the first to document carnivorous plants, and today there is over 600 identified

Competition among plants

is intense in areas with scarce nutrients

(Carnivory may be an adaptation for low-nutrient environments

When non-carnivorous neighboring are removed, pitcher plant growth increases)

Competition

non-trophic interaction between individuals where all species are negatively affected from sharing of limited resources

Interspecific competition

occurs between members of different species

Intraspecific competition

occurs between individuals of the same species

Resources are features required for

for growth, survival, and reproduction and can be consumed to the point of depletion

-Food, water, light, space, etc.

Species are additionally influenced by

temp, pH, salinity, etc. but because these things are not consumed they aren't resources

(Something could be considered a resource for some organisms but not for others)

Competition between species plays key roles in

in evolution and species distribution

Exploitative competition

when individuals reduce availability of a resource while using it (indirect)

ex. pitcher plants competing for nutrients and light

Interference competition

when species compete for access to a resource (direct)

-food

Competition may lead to Antagonistic Actions from species

-Interference in sessile species can include barnacles crushing each other while growing

-Interference in plants looks like individuals growing on or shading other species

-ALLELOPATHY is when one plant species releases toxins to harm other species

Competition reduces the amount of the resources available to individuals

but the effects are often unequal

-One species usually drive the other species to extinction

Ammensalism

when individuals of one species are harmed and individuals of the other aren't affected

Sometimes competition can occur from

distantly related species (rodents and ants)

Fundamental niche

full set of resources plus abiotic/biotic requirements

Realized niche

more restricted set of conditions a species is limited to

If ecological niches are similar

the superior competitor may drive the other species to extinction

Competitive exclusion

the idea that two species using a limiting resource can't coexist indefinitely

(There needs to be some sort of competitive coexistence)

Resource/ niche partitioning

when species use a resource in different ways

(Lizards partition habitat by living in different parts of trees, some cyanobacteria coexist by absorbing different light frequencies)

Environmental variation

is another mechanism allowing coexistence

(i.e. if the environment is dynamic (changes over space/time))

The Lokta- Volterra model supports

the idea that competition becomes more severe as population size increases

Zero growth isoclines

can determine whether a species will increase or decrease under certain conditions

Lokta Volta chart explained

-When isoclines don't cross = competitive exclusion

-Isocline above the other is driving the other species to extinction

-If the isoclines intersect = point where the species coexist

With coexistence, both species have a lower carrying capacity

Competitive reversal

is when an inferior competitor in one habitat becomes superior in another habitat

Competition influences

species distribution

Natural experiment

natural situation that reflects a controlled experiment

Disturbances

like fires or storms can kill/ damage some individuals while creating opportunities for others

(Some species can only exist in areas with regular disturbances)

Fugitive species

must disperse from one place to another as conditions change

Chapter 15: Mutualism and Commensalism

Positive interactions

where one/both species benefit and neither is harmed

2 forms of facilitation

-Mutualism- where both species benefit

-Commensalism- when one species benefits and the other is unaffected

(Growth, survival, or reproduction are increased by species interaction)

Symbiosis

2 species live in close physiological contact with each other

( can include parasitism- one benefits, one is harmed. commensalism and mutualism)

Benefits of positive interactions include

food, shelter and transport

mycorrhizae

symbiotic associations between the roots and various fungi (usually mutualisms)

-The mycorrhizal fungi increase the surface area for the plant to take up water and soil nutrients

-The plants supply the fungi with carbohydrates.

2 forms of mycorrhizae

Ectomycorrhizae- The fungus grows between root cells and forms a mantle around the root.

Arbuscular mycorrhizae: The fungus grows between and penetrates the cell walls of some root cells, forming a branched network called an arbuscule.

(positive interactions)

Relative neighbor effect (RNE)

= target species' performance with neighbors present minus its performance with neighbors removed

-RNE was generally positive at high-elevation sites: neighbors had a positive effect on the target species

-RNE was generally negative at low-elevation sites. - Plants tended to compete with one another in these relatively warm, low stress environments

Trophic

mutualism is receiving energy/ nutrients from the partner

(Example is coral and zooxanthellae)

Habitat

one provides the other with shelter or favorable habitat

(Example pistol shrimp digging burrow for goby fish)

Service

one partner performs ecological service for other

Pollination, dispersal, and removal of parasites

Mutualists are not

Mutualists are not altruistic (they are selfish)

Mutualists aren't selfless. In a mutualistic relationship both parties take action to promote their own well-being

(Mutualistic relationships must evolve so that there is net advantage for both)

what makes a partnership mutualistic

Net benefits must exceed the net costs for both parties to be considered mutualistic

If conditions change, a partnership may no longer be mutualistic

Obligate mutualism

both organisms depend on each other for survival

- Show clear signs of coevolution

- Common among mutualistic relationships

Facultative mutualism

two organisms don't have to live with each other

- Show few signs of coevolution

- Commensalism is always facultative for the species that does not benefit

Overexploitation

can be caused by cheaters who try to take advantage of their partner by increasing offspring production

(Can lead to penalties from the partner that was taken advantage of)

-ex, if the yuca moth lay too many eggs in the yuca plant, the plant will abort the flowers before the larvae hatch. Causing them to die.

When one species provides another with favorable habitat

it influences the distribution of the species

Many things like to live in seaweed, so seaweed distribution affects the distribution of crabs, urchins, etc.

Community composition and diversity

are influenced by positive interactions such as with cleaner fish and clients

In mutualism and commensalism

There will always be costs and benefits, but neither species can have net harm

Chapter 16: The Nature of Communities

Case study: Killer Algae

Caulerpa produces secondary compounds that deter fish and invertebrate herbivores.

(Scientists and fisherman want to know:How does this fast-spreading seaweed affect marine habitats and fisheries?How does one very abundant species influence the other species in the community?)

The study of communities looks at

multiple species interactions

Communities are defined by

the physical/ biological characteristics or ecological question that is being addressed

Physically defined community

encompass all species in an environment that is non-living, like a desert (dry)

Biologically defined community

encompasses all species in a living habitat like a coral reef or kelp forest (water)

How do scientists count all the species in a community?

Counting all species is bordering on impossible, so ecologists consider a subset of the species when defining a community

The subsets of species include:

Taxonomic affinity = all bird species in a community

Guild= group of species that all use the same resources

Functional groups= species that function in a similar way

Trophic interactions = the interactions with energy involved

(it is organized into food webs which represent energetic connections in a community)

Food web Trophic levels (from low to high):

Primary producers—autotrophs (make their own food; ex.plants)

Primary consumers—herbivores

Secondary consumers—carnivores•

Tertiary consumers—carnivores

Food webs don't

truly indicate how strong the interactions between levels are

Some species can span

multiple trophic levels and others may feed on multiple trophic levels as they mature

- these species are omnivores because they feed on multiple levels

Food webs do not include

important elements such as symbionts and detritivores (decomposers that break down waste and dead organisms)

Interactions webs

describe both trophic (vertical) and non-trophic (horizontal/ competition)

-These are important as food webs DON'T show non-trophic interactions

Community structure

is the set of characteristics that shape a community and provide the basis for generating hypothesis and experiments to understand how communities work

Species diversity

is a blend of species richness and species evenness

-Richness= number of species in a community

-Evenness= relative abundance of species

(assesses relative commonness/rarity of species)

Shannon Index

Lowest value = 0 (low diversity)

Higher values = 1.5- 3.5; rarely 4 (higher diversity)

- to do chart look at last number of pi In (pi) and compare

Biodiversity

diversity on multiple scales, from genes to species to communities

Genetic diversity

affects how viable a populations are, plays a role in species persistence (genetic variation between species)

-The number of different types of communities in an area speaks a lot to larger regional/ latitudinal scales