Communities biodiversity, issues keystone species habitats, niches Interactions: competition, predation, mutualism co-evolution

Wasps and Pieris caterpillars form an unusual three-step food chain Dining In Wasps and Pieris caterpillars form an unusual three-step food chain Wasp eggs layed inside caterpillar Caterpillar eaten up by larvae

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

Community = All the organisms in a particular area Description includes: Biodiversity -- Vegetation Response to disturbances Trophic structure (feeding relationships) Figure 36.1

A TERRESTRIAL FOOD CHAIN TROPHIC LEVEL Quaternary consumers What’s for lunch? Carnivore Carnivore Tertiary consumers Carnivore Carnivore Secondary consumers Carnivore Carnivore Primary consumers Herbivore Zooplankton Producers Plant Phytoplankton Figure 36.9A A TERRESTRIAL FOOD CHAIN AN AQUATIC FOOD CHAIN

Food webs often more real than food chains Tertiary and secondary consumers Wastes and dead organisms Food webs often more real than food chains Secondary and primary consumers Primary consumers “Follow the money” becomes Follow the food” to detect energy flow win community. Producers Detritivores (Plants, algae, phytoplankton) (Prokaryotes, fungi, certain animals) Figure 36.10

Energy supply limits the length of food chains 170 billion tons of biomass per year 10% conversion to biomass at next level Tertiary consumers 10 kcal Secondary consumers 100 kcal Primary consumers 1,000 kcal Producers 10,000 kcal 1,000,000 kcal of sunlight Figure 36.11

Consequence: a field of corn can support more vegetarians than meat-eaters TROPHIC LEVEL Secondary consumers Human meat-eaters Primary consumers Human vegetarians Cattle Corn Corn Producers Figure 36.12

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 Another mass extinction in progress? Wildlife preserves - do they work? Biodiversity hot spots: Should conservation efforts focus only on areas of high biodiversity? 4. Alien species

Communities 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

Community interactions There are four main types of relationships among species within communities Competition Parasitism, predation Commensalism Mutualism

Community interactions Interspecific competition occurs between two populations if they both require the same limited resource Resources include food, water, nesting sites Plants compete for sunlight, water, soil nutrients, space

The competitive exclusion principle Populations of two species cannot coexist in a community if their niches are nearly identical High tide Chthamalus Barnacle expt shows two outcomes possible: Remove blue barnacles, brown ones grow down and cover entire rock. Ther4, blues outcompeting brown for low space on rock. Remove brown ones, blue ones do NOT grow up. Ther4, resource (space on rock) has been divided and only brown are adapted to drier upper zones of rock. Balanus Ocean Low tide Figure 36.2

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 Predation is severe form of natural selection. Leads to many diverse adaptations designed to escape predation and to make more successful predators. Explains why the most successful parasite is not a fast killer. Examples: mistletoe on oaks, dodder on phosyn plants, fungal hyphae on nematodes

This reciprocal adaptation = coevolution As predators adapt to prey, natural selection also shapes the prey's defenses. This reciprocal adaptation = coevolution Example: Heliconius and the passionflower vine Eggs Sugar deposits Figure 36.3A

Prey gain protection against predators through a variety of defense mechanisms 1. 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 Many interesting chemicals from amphibs. Antibiotic megainan, anithestic. Figure 36.3B

3. Camouflage Example: gray tree frog 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

What are effects of predation? Eliminates weaker individuals keystone predator maintains diversity by reducing numbers of the strongest competitors in a community - Ex. sea star is a keystone predator 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

- Nitrogen-fixing bacteria and legumes Mutualism: both partners benefit Examples: - Nitrogen-fixing bacteria and legumes Acacia trees and the ants of the genus Pseudomyrmex Figure 36.5B

Disturbance is a prominent feature of most communities Disturbances include events such as storms, fires, floods, droughts, overgrazing, and human activities damage biological communities remove organisms alter the availability of resources Figure 36.6