11. Community and ecology: Tropic relationship

Question 1

Who is at the bottom of the pyramid?

Answer 1

Primary producers (mostly plants in terrestrial setting), they are called so because they are responsible for producing the biomass. They take in carbon dioxide in the presence of light and convert it into carbohydrates which are then consumed by the next tropic levels. (primary consumers)

Question 2

What are secondary consumers also known as?

Answer 2

Carnivores, they eat the primary consumers.

Question 3

What are decomposers?

Answer 3

Organisms that eat dead animals. These are important because they make nutrients to the primary producers.

Question 4

Why is less biomass as you move up in a pyramid?

Answer 4

Because energy is inefficiently converted in the next tropic level. There is some biomass loss as tropic levels increase.

Question 5

What is a food chain?

Answer 5

Linear relationship of how energy flows as one animal eats another.

Question 6

What is a food web?

Answer 6

It is an interconnected network of many food chains. It is meant to represent all of the feeding relationships within a community.

Question 7

What are parasitoids?

Answer 7

Insects that lays eggs in the body of another organism.

Question 8

How are 3 species connected (herbivores, parasitoids and plant network) in Costa Rica?

Answer 8

First comes the parasotoids on top, then herbivore and then plants.

Question 9

What are indirect effects?
How many species are needed in an indirect effect?

Answer 9

It is “what happens when one species alters the effect, that another has on the third.

At-least 3 species are required in an indirect effect.

Question 10

What are examples of indirect effect?

Answer 10

Exploitative or scramble effect

Question 11

When is exploitative effect an indirect effect?

Answer 11

If two species are competing for a 3rd SPECIE then it is known as an indirect effect.

If specie 1 eats specie 2, but specie 3 also eats specie 2, then specie 1 indirectly affects specie 2.

Question 12

What re Tropic Cascades?

Answer 12

Interactions between two tropics levels, cascades to the third. For example, predators (carnivores) eat primary consumers (herbivores) which is a negative effect.

Herbivores then eat plant. Again which is a negative effect.

But, Predators positively effect the plants because they eat primary consumers, which is a positive effect

Together they form a tropic cascade.

Question 13

What is a famous hypothesis by ‘HSS’? And what is this hypothesis also known as ?

Answer 13

HSS: Harrison Smith and Slobodkin

It is also known as the green world hypothesis.

They wondered why herbivores don’t eat all the plants.

They hypothesized that the carnivores keep down herbivores so they don’t limit plant growth.

Question 14

What is HSS’s hypothesis an example of?

Answer 14

An indirect tropic effect. It is a tropic cascade.

Question 15

What is an important characteristic of the tropic cascade?

Answer 15

They have alternating effects. For example, Predators have a negative effect on the herbivore, and herbivores have a negative effect on the plants, but carnivores have a positive effect on plants.

Question 16

What is an example of top-down control?

Answer 16

Carnivores eat herbivores so they don’t eat all the plants on earth.

That is predators keep the herbivores low, and predators are in the next tropic level.

Question 17

What is a test to see if predators affect the primary consumers in a top-down effect?

Answer 17

If the predators are removed, then the primary consumers should grow in size.

Question 18

What are bottom-up control?

Answer 18

Abundances kept low because of limited resources.

If the tropic level below does not have enough resources to support the the tropic level above it, it is called a bottom-up control.

Question 19

What is an experimental test to determine bottom-up control?

Answer 19

Add resources to the tropic level and see if the population in the next tropic level grows.

Question 20

What was spiller and Schoener’s study about?

Answer 20

Questions: Will anola lizard benefit plants or not?

Had seed grape shrubs at the bottom of the pyramid, Then these plants were fed on by herbivores beetles

These beetles were fed on by both spiders and Anolis lizard which ate both spiders and beetles

How it was carried out: Adding or removing lizards

Results:
Lizards had weak effect on the spiders but had a very strong effect on the beetles. When lizards were removed, more beetles were there that consumed plants.

Question 21

Why was experiment needed in Spiller and Schoener’s study?

Answer 21

Because, if the lizard ate only beetles, it would have been easy to determine the effects as an indirect effect, because they will be benefiting the plants.

But the lizard also ate the spiders, which meant they left behind the beetles, hence increasing the negative effect on the plants.

Hence an experiment was needed to determine the effects which DEPENDED ON the RELATIVE STRENGTHS OF INTERACTIONS between lizards and the beetles and lizards and spiders.

Question 22

How did fish affect plants?

Answer 22

Fish eat the larvae of dragon flies, having a negative effect on them

Fish also have an indirect negative effect on the adult dragonflies

But fish have an indirect positive effect on bees which are plant pollinators, that are eaten by adult dragon flies.

Bees have positive effect on plants and so do the fish.

Question 23

What were the results (data) from the fish affecting plants?

Answer 23

When there are no fish, there are more adult dragonflies, but when there are fish, there are less dragon flies.

Ponds in which there was fish had more / better pollinators, while plants surrounding the ponds without fish had fewer pollinators.

Question 24

Why is it hard to predict how species are interacting?

Answer 24

Indirect effects are as strong as direct effects, which make it hard to determine what actually is happening.

The outcomes depend on the interaction strength, hence experiments are needed to determine the effects of interactions. (potentially long term to understand the effects)

Question 25

Why are there so many plants and insects? And why is it hard for herbivory to eat plants?

Answer 25

1) plants are made up of lignin and cellulose, which are hard to digest, hence a specific set of microbiomes is needed in the guts of herbivores.

2) Plants have evolved chemical and defense mechanisms to not be eaten by herbivores.

Hence plants and animals are in an evolutionary arms race. Plants evolve ways to defend from animals, while animals develop ways to eat plants.

This arms race led to many species of plants and animals.

Question 26

What is an example of plant defense mechanism?

Answer 26

Milkweed plants produce milt that is toxic to most species but not monarch butterflies or caterpillars.

Once they turn into butterflies, they use that toxic liquid to warn other species that they are toxic.

This is an example of co-evolutionary process.

Question 27

What are secondary chemicals?

Answer 27

Plant toxins which are typically important in defense, which are different from primary chemicals that are used in plant metabolism.

Question 28

What is an example of secondary chemicals?

Answer 28

Alkaloids

Question 29

How do specialists insects use plant defense chemicals?

Answer 29

1) Feeding stimulants
2) Defense compounds

Question 30

What do plant-herbivore interaction result in?

Answer 30

Escalations and arms race, which are both important in generating biodiversity.

Question 31

What are the examples of alkaloids?

Answer 31

1) Coffee (Caffeine)
2) Tobacco (Nicotine)
3) opium poppy (Morphine)
4) Coca (Cocaine)

Question 32

What is a key in evolution of new plant or insect species?

Answer 32

Plant -insect Co-evolution

Paul Erlnich along with Peter H Raven thought plants evolved new defence mechanism to live away from insects, which would later evolve into new species

Insects also evolved to eat plants, which overtime evolved into new species.

Question 33

What are the challenges herbivores face, that don’t let them diversify as much?

Answer 33

1) many insects complete development on single well-defended plant, they must overcome all the plant defenses. EX: Monarch butterflies lay eggs on milkweed, grow on it etc, hence it must consume the plant, while vertebrates eat a bit of one plant and move on to the next one.

Vertebrates have mixed diets, they have food that follows different detoxifying pathways which avoids one toxification.

Some detoxification is also performed by the microbes in their guts in the fermentation chambers.

Hence they are not under selection for diversification.

Question 34

What is Rumen and Cecum?

Answer 34

Rumen: foregut
Cecum: Hind gut
Simple gut: A gut with many microbes