The 4 levels of ecology Communities and Ecosystems Chapter 20 Community ecology Natural Communities of the San Francisco Peninsula Community ALL the organisms (plants, animals, fungi, microbes) that live in a particular area Community ecology focuses on interactions between species Chaparral Redwood forest Foothill oak woodland Chaparral Grassland Urban bay Communities are identified by the dominant species (usually a plant) Foothill (or oak) woodland community Adaptations of Oaks Found at lower elevations along the coast and interior valleys Dominant plants are oaks Many are deciduous Acorns provide food for many animals, from acorn woodpeckers to deer Diversity of habitats Ranges from open savannah to dense forest with a welldeveloped understory Common in areas with summer drought Water-conserving strategies leathery leaves covered with a waxy layer to prevent drying out Deciduous: leaves shed when water is scarce; leaf out during winter/spring rains Developed toxins to discourage herbivores e.g. tannins in acorns
Threats to the Foothill Woodland Community What is Sudden Oak Death? Expanding suburbs/housing loss of habitat Poor regeneration of oaks Fewer predators over-abundance of acorn-eating animals (gophers, rabbits, ground squirrels, deer) Cattle grazing Fire Sudden Oak Death A plant disease threatening coastal forests in California and Oregon Caused by an exotic (nonnative) microbe, Phytophthora ramorum Over a million tanoak and oak trees in California have been killed There is no known cure Source: California Oak Mortality Task Force www.cnr.berkeley.edu/comtf/index.html A very different community: Redwood forest In fog-prone canyons or slopes Climate: moist, mild temperature Along coast of CA Redwoods can live for >1000 yrs and are the world s tallest trees (>300 ft) Under-story of Western sword fern, redwood sorrel Common animals: stellar jay, chickadee, banana slug Why is California so diverse? Different climates and landscapes Foggy coasts Hot central valley Cool mountains Deserts Supports a wide variety of communities alpine meadows, desert scrub, coastal wetlands, sandy beaches, oak woodlands, grasslands, redwood forests, riparian The redwood community Pollination: An example of co-evolution Co-evolution An adaptation in one species leads to an counter-adaptation in another species Many flowers have coevolved with the animals that pollinate them to improve pollen transfer Bats are nocturnal Bat-pollinated flowers are white, smell like bats, and large and sturdy
Interactions among species Species compete for resources One feeds on another (predator-prey) Both species can benefit Competition between species Two species compete for limited resources Avoiding competition Each species occupies a position in the community Lives in a particular area or habitat Plays a role: photosynthesizer, predator, prey, decomposer Interacts with other species Food Water Space Generally has a negative effect on the abundance of both species ( / ) Lion and hyena Predation (+/ ) One species (the predator) kills and eats the other (the prey) Predation is a key factor in evolution Eating and avoiding being eaten are prerequisites to reproductive success Black necked stilt Defenses against predation Mimicry Adaptations to avoid predators Fleeing Mechanical defenses Porcupine quills shells of clams and oysters Warning coloration A copycat adaptation in which one species looks like another characteristic of animals that use poisons Cryptic coloration color that blends in with surroundings = camouflage Scarlet king snake NOT venomous Eastern coral snake Venomous
Plants also have defenses against predation (+/ ) Spines and thorns Chemicals that make them toxic to herbivores Nicotine produced by tobacco plants Tannins in oaks Parasitism (+/ ) One organism benefits, the other is harmed The parasite obtains its nutrients by living on or in its host organism External parasites Mosquitoes, fleas suck blood from animals Aphids suck the sap of plants Internal parasites Tapeworms the protozoa that causes malaria Mutualism (+/+) Do humans form mutualistic relationships with other organisms? Both species benefit Pollination is a classic example of mutualism Ants eat the honeydew that aphids excrete and protect the aphids from predators. The bacteria E. coli live in our large intestine The majority of E. coli in our guts are beneficial. They produce vitamin K and breakdown fiber into glucose What is an ecosystem? Ecology of Ecosystems Includes interactions of organisms with the physical environment All the organisms in an area plus the physical environment Plants, animals, fungi, microorganisms Soil, water, air Includes both living and non-living things
Major ecosystem processes: Energy flow in ecosystems Energy flow and chemical cycling Heat Sun = source of energy Plants and algae convert the solar energy into food energy Energy is used for life functions Food chains: feeding relationships Herbivores Carnivores Decomposers The food chain continues Consumers Herbivores Carnivores Omnivores eat plants & animals Plants and algae The leaf is the primary site of photosynthesis Living organisms lose energy as heat Producers: The beginning of the food chain The species of a community are divided into different trophic levels based on their main sources of nutrition Producers Consumers growth, movement, reproduction Energy is lost as it passes through an ecosystem Solar-powered chemical factories Produce food for themselves and other organisms Capture solar energy and use it to build carbohydrates from CO2 and water Last step in the food chain Decomposers derive their energy from the dead material Decomposers break down organic substances, making them available to other organisms bacteria and fungi Increase nutrients in the soil Fungi decomposing a dead log
What limits the length of food chains? Most of the energy captured by plants is lost as energy passes through the food chain Only 10-15% of the calories an herbivore eats become stored as body mass available to the next link in the food chain. Energy loss in ecosystems Only a small % of nutrients consumed by lower-level consumers (herbivores) is available to higherlevel consumers An energy pyramid is a diagram that shows the cumulative loss of energy from a food chain. Energy flow applies to the human population Example of an ecosystem Estuary Where fresh water meets the ocean One of the most productive ecosystems in the world Home to more than 2/3 of the fish and shellfish consumed by humans. Rich in decomposers Fragile ecosystem Eating producers instead of consumers reduces our impact on the environment Figure 19.27 Tropical rain forest Layers of plants Found near the equator Warm temp Lots of rain thru/out the year Rainforest layers Leafy canopy >80 inches (200 cm) per year High humidity Figure 19.34a Most tall trees Home to about half of all plant species Poor penetration of sunlight to ground not many plants in understory or on forest floor
Value of biodiversity Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Biodiversity Sources of many medicines. Wild species, like many marine species, provide us with food. Food We are seeing a precipitous drop in Earth s great variety of life Wild species, like the nine-banded armadillo, play a role in medical research. Medicine Many drugs are derived from living organisms Value of biodiversity Yet every day we re losing species Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Agriculture Wild species, like rubber trees, can provide a product indefinitely if the forest is not destroyed. Pollination Wild species, like ladybugs, play a role in biological control of agricultural pests. Pest control Loss of the rainforest Rainforests should cover about 12% of the globe. However, as of 2007, they only cover around 5%. Many rainforest species are disappearing Due to deforestation, habitat loss and pollution Commercial logging Renewable resources (bat): Merlin D. Tuttle/BatConservation International; (rubber): BrynCampbell/Stone/Getty Images; (lady bug): Anthony Mercieca/Photo Researchers, Inc. Does biodiversity matter? Large scale changes in the environment could have catastrophic consequences Protecting Biodiversity How can we reduce human impact? Stabilize the human population Reduce consumption Reduce pollution Develop alternative energy Preserve non-replaceable resources 42