Communities biodiversity, issues keystone species habitats, niches Interactions:

Communitiesbiodiversity, issues keystone specieshabitats, niches

Interactions:competition, predation,mutualism, commensalismco-evolution

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• Wasps and Pieris caterpillars form a food chain

• Wasp eggs layed inside caterpillar

– Caterpillar eaten up by larvae

Dining In


• A second wasp can detect wasp larvae inside these caterpillars

– and will deposit her own eggs inside of the first wasp’s larvae


• Finally, yet another wasp, a chalcid, may lay its eggs inside the second wasp’s larvae

• Only the chalcid wasp’s larvae emerge from the caterpillar carcass


• = All the organisms in a particular area

• Description includes:– Trophic structure (feeding relationships)

-- Vegetation-- Biodiversity -- Response to disturbances

Community

Figure 36.1


Figure 36.9A

TROPHIC LEVEL

Quaternaryconsumers

Tertiaryconsumers

Carnivore Carnivore

Carnivore Carnivore

Carnivore Carnivore

Herbivore Zooplankton

Plant Phytoplankton

Secondaryconsumers

Primaryconsumers

Producers

A TERRESTRIAL FOOD CHAIN AN AQUATIC FOOD CHAIN

What’s for lunch?


Figure 36.10

Tertiaryandsecondaryconsumers

Secondaryandprimaryconsumers

Primaryconsumers

Producers

(Plants, algae,phytoplankton)

Detritivores

(Prokaryotes, fungi,certain animals)

Wastes anddead organismsFood webs

oftenmore real thanfood chains

Food webs reveal the flow of energy


• 170 billion tons of biomass per year

Figure 36.11

Tertiaryconsumers

Secondaryconsumers

Primaryconsumers

Producers

10 kcal

100 kcal

1,000kcal

10,000 kcal

1,000,000 kcal of sunlight

Energy supply limits the length of food chains

Avg. 10% conversion of biomassto next level

Endothermic animals convert only 2% Plants

convert 30-85%


• Consequences:

• Low density of large carnivores

• a field of corn can support more vegetarians than carnivores.

Figure 36.12

Secondaryconsumers

Primaryconsumers

Producers

Humanvegetarians

Corn

Humanmeat-eaters

Cattle

Corn

TROPHIC LEVEL


• Chemicals are concentrated in food chains by biological magnification

Figure 38.3B

DDT in water0.000003 ppm

DDT inzooplankton0.04 ppm

DDT insmall fish0.5 ppm

DDT inlarge fish2 ppm

DDT infish-eating birds25 ppm

DDT concentration:increase of10 million times


• Biodiversity is the variety of organisms that make up a community

• Components:

– Species variety: total number of different species in the community

– relative abundance of different species

– Genetic variation within each species


Biodiversity - current issues

1. Another mass extinction in progress?

2. Wildlife preserves - do they work? 3. Biodiversity hot spots: Should

conservation efforts focus only on areas of high biodiversity?

4. Alien species


• Habitat is the environment in which an organism lives.

• A population's niche is its role in the community

– How it uses the biotic and abiotic resources of its habitat

Communities


• There are four main types of relationships among species within communities

– Competition

– Parasitism, predation

– Commensalism

– Mutualism

Community interactions


Community interactions

Interspecific competition occurs between

two populations if they both require the same

limited resource


• The competitive exclusion principle

– Populations of two species cannot coexist in a community if their niches are nearly identical

Figure 36.2

Hightide

Chthamalus

Balanus

Lowtide

Ocean


• Competition between species with identical niches has two possible outcomes– One population will eventually eliminate the other

– Natural selection may lead to resource partitioning (division)


• Predation is an interaction where one species eats another

– consumer = predator

– food species = prey

• Parasitism is a form of predation

– Parasite, host

– Not immediately lethal


• Some plants have evolved parasitic ways of obtaining food from other plants

– Dodder taps into the host’s vascular tissue

Other modes of nutrition for plants:

Figure 32.12A


– Mistletoe siphons sap from vascular tissue of its host plants

Figure 32.12B


• As predators adapt to prey, natural selection also shapes the prey's defenses.

• This reciprocal adaptation = coevolution

– Example: Heliconius and the passionflower vine

Figure 36.3A

Eggs

Sugardeposits


• Carnivorous plants obtain nutrients from animal tissues

– Sundew and Venus flytrap use insects as a source of minerals

– enables them to thrive in highly acidic soil

Figure 32.12C, D


• Prey gain protection against predators through a variety of defense mechanisms1. Mechanical defenses, such as the quills of a porcupine


2. Chemical defenses

– Animals are often brightly colored to warn predators

– Example: the poison-arrow frog

Figure 36.3B


3. Camouflage

Figure 36.3C


4. Batesian mimicry occurs when a harmless species mimics a harmful one– mimicry can involve behavior

– hawkmoth larva puffs up its head to mimic the head of a snake

Figure 36.3D


• Eliminates weaker individuals

• keystone predator maintains diversity by reducing numbers of the strongest competitors in a community

- Ex. sea star is a keystone predator

What are effects of predation?

Figure 36.4A


• Predation by killer whales on sea otters, allowing sea urchins to overgraze on kelp

– Sea otters represent the keystone species

Figure 36.4B


• Commensalism - one partner benefits and the other is unaffected

• Examples

- Algae that grow on the shells of sea turtles

– Barnacles that attach to whales

– Birds that feed on insects flushed out of the grass by grazing cattle


• Mutualism:

both partners benefit

Example:

– Acacia trees and the ants of the genus Pseudomyrmex

Figure 36.5B


• Mutualism

• mycorrhizae

– fungal threads increase plant's absorption of nutrients and water

– fungus receives nutrients from the plant

Figure 32.11


• nodules in the plant roots contain bacteria that convert N2 gas to soluble NO3-, NH4+

Legumes and certain other plants house nitrogen-fixing bacteria

Figure 32.14A

Shoot

Nodules

Roots


Figure 32.13

ATMOSPHERE

N2

N2Nitrogen-fixing

bacteria

Ammonifyingbacteria

Organicmaterial

NH4+

(ammonium) Nitrifyingbacteria

NO3–

(nitrate)

Root

NH4+

Aminoacids

Soil

Nitrogen-fixing bacteria and legumes


• Disturbances include events such as storms, fires, floods, droughts, overgrazing, and human activities – damage biological communities

– remove organisms

– alter the availability of resources

Disturbance is a prominent feature of most communities

Figure 36.6

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Communities biodiversity, issues keystone species habitats, niches Interactions: