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• There are different interspecific

interactions, relationships between the

species of a community (what’s the

definition of a community again?).

Here’s one. And how evolution works.

• While you’re at it, what’s the definition

of “interspecific”?

• How about a POGIL?

Introduction

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

https://www.youtube.com/watch?v=vMG-LWyNcAs

https://imgur.com/kkxnYd6

• Possible interspecific interactions are introduced in

Table 53.1, and are symbolized by the positive or

negative affect of the interaction on the individual

populations.

• Note the comparison

with symbiotic

relationships. Are these

all symbiosis?

1. Populations may be linked by

competition, predation, mutualism and

commensalism.


• Competition.

• Interspecific competition for resources can

occur when resources are in short supply.

• There is potential for competition between

any two species that need the same limited

resource.

• The competitive exclusion principle: two

species with similar needs for the same limiting

resources cannot coexist in the same place.


• The ecological niche is the sum total of an

organism’s use of abiotic/biotic resources in the

environment.

• The competitive exclusion principle can be

restated to say that two species cannot coexist

in a community if their niches are identical.

• This is the “this town’s not big enough for the

both of us” principle.

• What are some possible outcomes of this

competition?


• Classic experiments confirm this principle.

Which one out-competes the other?

Fig. 53.2


• Resource partitioning is the differentiation of

niches that enables two similar species to

coexist in a community.

Fig. 53.2Fig. 53.3


• Predation.

• A predator eats prey.

• Herbivory, in which animals eat plants.

• In parasitism, predators live on/in a host and

depend on the host for nutrition. Symbiosis?

Watch this wasp and his cockroach host!

• Predator adaptations: many important feeding

adaptations of predators are both obvious and

familiar.

• Claws, teeth, fangs, poison, heat-sensing

organs, speed, and agility.


https://www.youtube.com/watch?v=Kg4-MW009k0

• Plant defenses against herbivores include chemical

compounds that are toxic.

• Animal defenses against predators.

• Behavioral defenses include fleeing, hiding, self-

defense, noises, and mobbing.

• Camouflage includes cryptic coloration,

deceptive markings.

Fig. 53.5Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

• Mechanical defenses include spines.

• Chemical defenses include odors and toxins

• Aposematic coloration is indicated by

warning colors, and is sometimes associated

with other defenses (toxins).

Fig. 53.6


• Mimicry is when organisms resemble other

species.

• Batesian mimicry is where a harmless

species mimics a harmful one.

Fig. 53.7


• Müllerian mimicry is where two or more

unpalatable species resemble each other, like

this bee and its wasp mimic.


Fig. 53.8

• Mutualism is where

two species benefit from

their interaction.

• Commensalism is

where one species

benefits from the

interaction, but other

is not affected.

• An example would

be barnacles that

attach to a whale.

• How about this one?Fig. 53.9


Here’s a really neat look at termites!

• https://www.youtube.com/watch?v=e02keFYEW

eU

• 7 minutes

https://www.youtube.com/watch?v=e02keFYEWeU

• Coevolution and interspecific interactions.

• Coevolution refers to reciprocal evolutionary

adaptations of two interacting species.

• When one species evolves, it exerts selective

pressure on the other to evolve to continue the

interaction.

• For example, adaptations for speed in both

cheetahs and antelopes. Look at these.

• Flowers and their pollinators are classic

examples.


https://www.youtube.com/watch?v=DRxsP2YMaOI

SC.912.L.17.9

Use a food web to identify and distinguish producers, consumers, and decomposers. Explain the pathway of energy transfer

through trophic levels and the reduction of available energy at successive energy levels.

4. Design an ecosystem that displays the

interdependence of producers, consumers and

decomposers.

Develop a path of the energy that follows

through each of the trophic levels within your

ecosystem and relate the cause and effect of

changes in predator and prey

3. Use a food web to identify and distinguish

producers, consumers, and decomposes

Explain the pathway of energy transfer

through trophic levels and the reduction of

available energy at successive trophic levels

• The trophic structure of a community is determined

by the feeding relationships between organisms.

• The transfer of food energy from its source in

photosynthetic organisms through herbivores and

carnivores is called the food chain.

2. Trophic structure is a key factor in

community dynamics


• Charles Elton first

pointed out that the

length of a food

chain is usually four

or five links, called

trophic levels.

• He also recognized

that food chains are

not isolated units but

are hooked together

into food webs.

Fig. 53.10


Marine Ecosystem: can you draw a food web?

• Food webs.

• Who eats whom in a

community?

• Which ones are the

producers here?

• What transforms

food chains into

food webs?

• Which ones feed on

only one other type?

Fig. 53.11Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

• Dominant species are those in a community that

have the highest abundance or highest biomass (the

sum weight of all individuals in a population).

• If we remove a dominant species from a

community, it can change the entire community

structure.

3. Dominant species and keystone species

exert strong controls on community

structure


• Keystone species

exert an important

regulating effect

on other species

in a community.

Fig. 53.14


The Pisaster experiments done by Robert

Paine in Washington and elsewhere

• Demonstrated that some species that were not

dominant in terms of biomass or numbers exert a

high amount of control on the community they are

a part of. Often at the top of the food chain, can

you see how these keystone species are part of a

feedback system much like we have seen with

blood sugar and lactose and other chemicals, just

on a larger scale? Here’s his story. 20 min.

• Regulatory systems evolve naturally to result in

the homeostatic balances you see in nature.

http://www.hhmi.org/biointeractive/some-animals-are-more-equal-others-keystone-species-and-trophic-cascades

• If they are removed, community structure is greatly

affected. See this classic story of wolves in Yellowstone.

Fig. 53.15


http://www.flixxy.com/how-wolves-changed-an-entire-ecosystem.htm

• A general model of chemical cycling.

• There are four main reservoirs of elements and

processes that transfer elements between

reservoirs.

• Reservoirs are defined by two characteristics,

whether it contains organic or inorganic

materials, and whether or not the materials are

directly usable by organisms.

1. Biological and geologic processes move

nutrients between organic and inorganic

compartments. Let’s follow chemicals…



Fig. 54.15

• The carbon cycle fits the generalized scheme of

biogeochemical cycles better than water.


Fig. 54.17

• The water cycle is mostly a physical process (evaporation,

condensation), but part is biological, right?


Fig. 54.16

Did you get it right?

• Respiration and dehydration

synthesis creates new water, and

photosynthesis and hydrolysis

breaks water molecules apart.

• The nitrogen cycle. You DON”T need to know this

for the EOC, but let’s take a look.

• Nitrogen enters ecosystems through two natural

pathways.

• Atmospheric deposition, where usable nitrogen

is added to the soil by rain or dust.

• Nitrogen fixation, where certain prokaryotes

convert N2 to forms that can be used to

synthesize nitrogenous organic compounds like

amino acids.



Fig. 54.18

• Recent studies indicate that human activities have

approximately doubled the worldwide supply of

fixed nitrogen, due to the use of fertilizers,

cultivation of legumes, and burning.

• This may increase the amount of nitrogen

oxides in the atmosphere and contribute to

atmospheric warming, depletion of ozone and

possibly acid rain.


• This may cause big problems in the future with the balance of this cycle, just as human burning of fossil fuels is causing problems related to the carbon cycle.

• Two more examples of human activity affecting the ecosystem in negative ways.


Review and connect…

• Disturbances to food webs obviously are

changing population sizes.

• What kind of limiting factor are the killer whales?

• Now let’s look at another phenomenon that

involves changes in population size…succession.

• How about a POGIL?

• Ecological succession is the transition in species

composition over ecological time.

• Primary succession begins in a lifeless area where

soil has not yet formed. Like after a volcano, on

volcanic islands like Hawaii and the Galapagos.

• Secondary succession occurs when most if not all

life is extinguished, but soil remains.

3. Ecological succession is the sequence of

community changes after a disturbance


• In primary succession, mosses and lichens colonize

first and cause the development of soil. These are

Pioneer communities.

• An example would be when a glacier has retreated.


Fig. 53.19


• Secondary succession occurs where an existing

community has been cleared by some event, such as

fire or clear-cutting, but the soil is left intact.

• Grasses grow first, then trees and other

organisms. Climax communities?


A marine food web is shown below. Which of the

following would be a long-term effect of removing

baleen whales from the ecosystem represented by

this food web? A. The krill population would increase

B. The orca population would increase

C. The phytoplankton population would increase

D. The large fish and squid population would increase

An arctic food web is shown below. Suppose that the

lemming population is removed from this food web. Which

of the following will be a short-term effect of this change? A. The arctic fox population will increase

B. The polar bear population will increase

C. the caribou population will decrease

D. The snowy owl population will decrease

Part of an ocean food web is shown below. Which of the

organisms in the web are secondary consumers?

A. blue sprat and mackerel

B. mackerel, tuna, and shark

C. blue sprat and zooplankton

D. blue sprat, mackerel, tuna, and shark

A meadow food web is shown below. Which

organisms are in the trophic levels that sustains this

ecosystem?

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