Ecology: Study Guide



Ecology: Study Guide

An organism is an individual.

A population is a group of individuals that live in the same area, can interbreed, and share the same gene pool.

A community is composed of all the different populations of species that live in a given area.

An ecosystem is a collection of all the organisms that live in a particular area along with their nonliving, physical environment.

• Abiotic— An ecosystem has a set of environmental or non-living factors that define what will live there. These are called abiotic factors. For example: water, temperature, light, air, soil type, topography.

• Biotic- anything that is living. For example, all plants and animals of an ecosystem.

A biome is a group of ecosystems that have similar climates and dominant communities.

A biosphere is a portion of Earth that contains all ecosystems.

Niche

This is the role an organism plays in its habitat, not just where it lives, but how it functions in that community. Many similar species may share a habitat but no two species can occupy the same niche. When niches overlap competition will result. For example, rabbit and a deer may compete because they both are herbivores.

Species interactions

Symbiosis – a relationship between 2 species that live in close association.

Parasitism – One organism feeds on another (the host). The host is usually harmed but not killed.

Ex. Dogs and fleas.

Mutualism – Symbiotic relationship when both species benefit.

Ex. Cleaner fish removing parasites from large predator fish.

Commensalism – Two organisms live in close association with each other.

One organism is helped by the association while the other is neither helped nor harmed.

Ex. orchids and trees, birds nesting in trees.

Predation

A predator feeds off other organisms but doesn’t live on or in them, unlike parasites. Many predator/prey adaptations arose by co-evolution.

Predator/Prey Dynamics

Predators affect the population size of their prey, but as the number of prey decreases so does the number of predators. The relationship is called a predator-prey cycle, and it shows how each regulates the population of the other in a natural setting. Problems can occur when populations are not controlled. This may be due to introducing a new species that has no natural predator. Some populations may also die off due to a lack of resources. Understanding population growth is important as each population impacts others within an ecosystem.

Community stability

▪ The way a community comes into being is called ecological succession.

▪ It begins in a barren area (volcanic island, glacier retreat) where a pioneer species colonizes the region. These species reproduce and disperse well.

▪ Lichens are the main pioneer species. They can break down the minerals in rocks to begin to form soil. This process is called primary succession.

▪ As soil forms from decomposition of earlier plants, small plants can grow. They die and their organic matter enriches the soil for larger plants to grow. Eventually larger and larger species can inhabit that area.

▪ Secondary succession—occurs in a disturbed area where soil is already in place (e.g. after forest fire).

All ecosystems change over time. As they change the type of organisms that live there also changes. Often one community is replaced by another and this is known as succession.

Ecosystems are sometimes destroyed by natural catastrophes such as volcanoes, earthquakes, fires, floods. If this leaves behind barren land the process that follows is known as Primary Succession.

After the volcano erupts, the surrounding land is barren, lifeless and rocky. The first organisms to colonize the area are called pioneer species. These are usually small fast growing plants that reproduce quickly. The pioneer organisms include lichens and mosses, which help form the soil layer so that other species may also live there. Grasses and weeds can then grow and they often replace the lichens and mosses. Trees and shrubs colonize next and outcompete and replace the grasses, eventually leading to a stable forest community made up of oaks and maples. This is called a climax community. At this point equilibrium in the ecosystem is restored.

Succession also occurs when a tree falls down in a forest or in areas that have natural rainy and drought cycles. During the rains one type of grass may dominate, but during the drought other types may dominate. This type of succession is known as secondary succession.

Ecosystems

An Ecosystem is a collection of organisms and their physical environment all interconnected by the energy flow between them. Despite the visible differences between ecosystems, they all possess some common features:

1. Primary producers—aka autotrophs or self-feeders. They capture energy from sunlight or inorganic compounds and turn it into organic compounds (e.g. plants, algae).

2. Consumers—aka heterotrophs. Feed on tissues of other organisms (e.g. herbivores, carnivores, scavengers).

3. Decomposers—heterotrophic bacteria and fungi. They secrete enzymes that breakdown organic compounds & then absorb them (extracellular digestion). They return nutrients to the environment. Detritivores are heterotrophs that eat decomposing organic matter (intracellular digestion). They include earthworms and they play a vital role in nutrient cycling.

Feeding Relationships

All organisms in an ecosystem can be grouped in a hierarchy of feeding relationships called trophic levels.

▪ Producers are at the first trophic level. When a herbivore eats them, producers give up their energy to the consumer.

▪ Carnivores eat other animals.

▪ Omnivores eat both plants and animals.

Food chains show what eats what within a community. They all start with a producer, such as a plant or algae that can use the energy from the sun in the process of photosynthesis. Next come the herbivores, followed by omnivores or carnivores

Food webs are made up of many food chains. They are a more complete picture of the feeding relationships within a community, because most organisms eat more than one kind of food.

Food webs show how organisms feed and help us understand each organism’s niche or role in the community.

For example, in the food web to the right if you follow one of the chains you will see that oak leaves represent primary producer, vole is the primary consumer, weasel is the secondary consumer and the fox is the tertiary consumer.

Energy flow

As energy flows through an ecosystem only 10% of energy available in one trophic level is passed to the next. 90% of it is lost as heat. When an organism eats food it does not gain all the mass of the food. For example if a zebra eats 10kg of grass it does not increase in mass by 10kg. This is because a lot of the energy stored in the grass is lost. As the zebra eats the grass it uses some of the energy to run and to grow. Some is stored as fat and muscle in the zebra’s body. Some is lost as heat. From producer to consumer the amount of energy within each trophic level decreases.

Ecological Pyramids

Trophic levels in an ecosystem can be described as pyramids. Primary producers are on the bottom & consumers on top.

▪ Biomass pyramids depict the dry weight of all the organisms at each tier. For terrestrial ecosystems the base is wide and narrows to the top. For marine ones it’s inverted because phytoplankton grow and reproduce so fast, they can support a vast biomass.

▪ Energy pyramids show the amount of energy available at each trophic level. Their shape is always wide at the bottom and narrow at the top.

Cycles:

Autotrophs in an ecosystem require energy, hydrogen, carbon, oxygen, nitrogen and phosphorous. There are cycles for each of these which describe how nutrients are shuffled between an environment and its organisms.

Water cycle

▪ Hydrologic cycle is the movement of water from its main reservoir (ocean) to the atmosphere (evaporation from bodies of water and transpiration from plants), forming clouds (condensation) and back down to the soil or ocean (precipitation) and back into the ocean (runoff).

Carbon cycle

▪ Most carbon is in the deep ocean and sediments and is slowly cycled. The rest is cycled more quickly between shallow ocean, atmosphere, soil and living things.

▪ Plants take in CO2 from atmosphere and turn it into glucose and other products.

▪ Animals take in the glucose and break it down and release CO2.

▪ Animals and plants die, decomposers return their carbon to the soil.

▪ Carbon in sediments can be burned as fossil fuels. Driving cars, burning of trees and forests, burning of coal will release the CO2 into the atmosphere.

Global warming

▪ Gases in our atmosphere trap the sun’s heat. Without this, Earth would be cold and uninhabitable. This is known as the greenhouse effect.

▪ Because we burn fossil fuels we have an excess build up of greenhouse gases, especially CO2 .

▪ A majority of scientists believe that this increase in CO2 and other gases like methane are causing the temperature on earth to increase. This phenomenon has come to be known as global warming.

Nitrogen cycle

Nitrogen is necessary for bacteria, plants, and animals. Plants and animals both obtain their nitrogen after it has been fixed by bacteria. Most nitrogen is in the form of N2 (atmospheric) which very few organisms can use. There are 4 basic mechanisms for cycling nitrogen:

1. Nitrogen fixation—some bacteria convert N2 to ammonia (NH3). This form can be used by other organisms.

2. Decomposition and ammonification—decomposers use the proteins from dead organisms. They turn the nitrogen into NH3 (ammonia) and NH4+ which plants can use.

3. Nitrification—other bacteria act on NH3 and NH4+ resulting in NO2- (nitrite) that is further converted to NO3- (nitrate) that plants can use.

4. Denitrification—other bacteria can take NO3- in soil and turn it into N2 which is released as a gas into the atmosphere.

Biomes – a group of ecosystems with similar conditions

|Biome |Abiotic Factors |Biotic Factors |Geographic Distribution |

| | |Plants & Animals | |

|Tundra |frozen top soil, snow, cold temperatures |Plants: short shrubs, grasses, lichens, and |northernmost regions of Asia, Europe, and |

| | |mosses |North America |

| | |Animals: insects, reindeer, caribou, wolves, | |

| | |brown bears | |

|Taiga |cold to moderate temperatures, warm summers, |Plants: coniferous trees (evergreens) |just south of the tundra |

| |fertile soil, precipitation |Animals: black bears, deer, squirrels, | |

| | |rabbits, moose, elk, insects | |

|Deciduous forest |distinct hot and cold seasons, high |Plants: Deciduous trees, conifers, flowering |Northeastern United States, Southeastern |

| |precipitation, fertile soil |shrubs, herbs, moss, and ferns |Canada, Europe, parts of Asia, China, and |

| | |Animals: Deer, black bears, bobcats, |Australia |

| | |squirrels, raccoons, skunks, birds, turkeys | |

|Grasslands |warm summers, cold winters, seasonal |Plants: low growing, lush plants and a few | |

| |precipitation, fertile soil, occasional |trees | |

| |wildfires | | |

| | |Animals: a variety of large herbivores like | |

| | |elephants, kangaroos, zebras, giraffes, | |

| | |antelope, insects | |

| | | | |

|Desert |dry (less than 30cm of rain/year), variable |Plants: cacti, sagebrush, and other succulent | |

| |temperatures, mineral rich soil that lacks |plants | |

| |organic nutrients needed to grow food | | |

| | |Animals: birds, small rodents, lizards, and | |

| | |snakes | |

|Tropical Rainforest |high rainfall, hot temperatures, acidic |Plants: Broad-leaf evergreens that form |South and Central America, Southeast Asia, |

| |nutrient-poor soil |canopies, ferns, climbing plants, and orchids |southern India, and northeastern Australia |

| | |Animals: insects, birds, monkeys, lizards, | |

| | |snakes, sloths anteaters, mostly in the canopy| |

Carrying capacity of a population is reached when no more organisms can be sustained by the resources of the environment.

Food web stability:

A food web has many connections among its producers, consumers, and decomposers. It displays these relationships in an intricate web. A food chain, on the other hand, only shows one set of relationships from a producer to a primary consumer to a secondary consumer. A food web is therefore more accurate and more stable than a food chain because it will handle changes in the community much easier. See the pictures below for clarification.

[pic] [pic]

FOOD WEB

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