All organisms living together in a place are called a

Planet Earth is inhabited by millions of species—at least! Because different species often inhabit the same spaces and share—or compete for—the same resources, they interact in a variety of ways, known collectively as symbiosis. There are four main symbiotic relationships: mutualism, commensalism, parasitism, and competition.

To explore these relationships, let’s consider a natural ecosystem such as the ocean. Oceanic environments are known for their species diversity. Imagine you are on a diving expedition to explore the worlds beneath the waves. If we were in the warm waters of the Pacific or Indian Oceans, we’d likely spot an excellent example of mutualism: the relationship between clownfish and sea anemones. In a mutualistic relationship, both species benefit. Sea anemones live attached to the surface of coral reefs. They trap their prey with stinging cells called nematocysts, which are located on their tentacles. Nematocysts release toxins when a small animal contacts an anemone’s tentacle. This paralyzes the stung animal, allowing the anemone to easily bring the animal into its mouth for ingestion.

While other fish succumb to these toxic stings, clownfish secrete a substance in the mucus covering their bodies that suppresses the firing of nematocysts. This allows the clownfish to swim comfortably between the tentacles of anemones, creating a protected environment in which potential predators are killed off by anemone stings. This clearly benefits the clownfish, but how about the sea anemones? The brightly-colored clownfish attract other fish looking for a meal. These unsuspecting would-be predators are then caught and eaten by the anemones.

As we continue in our imaginary deep-sea voyage, we may observe the commensalistic relationship that exists between barnacles and humpback whales. Commensalism happens when one species lives with, on, or in another species, known as the host. The host species neither benefits nor is harmed from the relationship. In our imagined example, various species of barnacles attach themselves to the skin of whales. Scientists have not discovered the exact mechanism by which barnacles are able to do this, but it does not appear to bother the whales. How do the barnacles benefit from this unlikely relationship? The huge whales transport the tiny barnacles to plankton-rich waters, where both species feast upon the abundant microorganisms that live there.

Of course, some symbiotic relationships do cause harm. In parasitism, one species (the parasite) lives with, on, or in a host species, at the expense of the host species. Unlike in predation, the host is not immediately killed by the parasite, though it may sicken and die over time. Examples of common parasites found in the ocean include nematodes, leeches, and barnacles. That’s right—though barnacles exist commensally with whales, they are parasites for swimming crabs. A barnacle may root itself within a crab’s reproductive system. While the crab does not die from this interaction, its reproductive capabilities are greatly diminished.

The last example of symbiosis we will explore on our imaginary dive is competition—the struggle among organisms for the same limited resources in an ecosystem. Competition can happen between members of the same species (intraspecific competition) and between different species (interspecific competition). An example of interspecific competition in the ocean is the relationship between corals and sponges. Sponges are very abundant in coral reefs. If they become too successful, however, they take needed food and other resources from the corals that make up the reef. Sponges may outcompete corals for resources in the short term, but if too many corals die, the reef itself becomes damaged. This is bad for the sponges, which may themselves begin to die off until the reef is balanced again.

Symbiotic relationships can be useful measures of an ecosystem’s health. For example, large tracts of coral reefs are severely damaged or dead because of recent increases in ocean temperature due to climate change. The temperature increase induces coral to expel the algae that live mutualistically within them. Without their algae, the coral turn white and die. This loss of symbiosis is an early sign of declining coral health and speaks to the importance not only of studying symbiosis within marine environments, but also of examining the negative impacts that humans can have on these interactions. In the words of National Geographic Explorer Sylvia Earle: “We need to respect the oceans and take care of them as if our lives depend on it. Because they do.”

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ECOSYSTEMS AND BIOMES

Definition of Concepts

Ecology: The study of the interrelationships between living organisms and the living and non-living components and processes in an environment

Biome: A major ecological region within which plant and animal communities are similar in general characteristics and in their relationships to the physical environment. Eg. vegetation zones such as the Tundra, Desert & Rainforests.

Ecosystem: The collection of all living organisms in a geographic area, together with all the living and non-living things with which they interact.

·    Acquatic Ecosystems (water-based) ecosystems

·    Terrestral Ecosystems (land-based) ecosystems.

Population: A group of organisms of the same kind living in a given area

Natural Community: Populations of different plant and animal species interacting among themselves in an area.

Habitat: The specific physical location where a particular organism lives or is adapted to live in a community.

Ecological Niche: An organism’s role or occupation within a community.

Bio-geography: A study of the distribution of plants and animals, the diverse spatial patterns they create, and the physical and biological processes (past & present) that produce this distribution.

STRUCTURE OF ECOSYSTEMS

1. Boitic and Abiotic

Every ecosystem is composed of two basic units:

a)         Biota: the living organisms - all plant & animal species

b)        Abiotic: the non-living physical and chemical component consisting of wind, temperature, water, soil, precipitation etc.

The single abiotic factor most lacking in a particular environment is termed a Limiting Factor. e.g. water – in a desert and temperature - Tundra.

The variation in physical factors that a population can withstand and continue to thrive in an environment is termed Range of Tolerance.

CATEGORIES OF ORGANISMS

1. PRODUCERS:

Green plants that carry on photosynthesis. Producers are termed auto-trophs because they are self-nourished – they do not depend on other species to feed.

During photosynthesis, plants capture light energy with their chlorophyll and use it to convert carbon dioxide and moisture (absorbed from air) into sugar (chemical energy). Oxygen is released as a by-product

Every major ecosystem has its particular green plants that carry on photosynthesis and release chemical energy (carbohydrates, protein etc.) on which non-producers feed. (algae & plankton in aquatic systems, plants in terrestrial systems)

2. CONSUMERS:

a) Consumers are heterotrophs (other-nourished) for they rely on chlorophyll-containing plants or the products of such plants for nourishment.

b) Consumers are subdivided into groups according to their food source.

Primary consumers: Species that feed directly on producers (plant-eating species). They are also called Herbivores. E.g. elephants, goats, cattle

Secondary Consumers: Species that feed on primary consumers. Secondary and higher order consumers are called Carnivores. E.g. fox, cat.

Tertiary and higher level Consumers: Species that obtain their nourishment by eating other meat-eating species. E.g. tiger

Multiple level Consumers: Species that obtain their nourishment from eating both plants and animal species. Also called Omnivores

3. DECOMPOSERS:

They are the final link in the food chain. Comprise of organisms that feed on dead matter and break it down to release chemical energy back into the soil for plants to re-use them. E.g. fungi, bacteria, insects, worms and others.

Detritivores: feed on detritus matter (dead plants and animals) e.g. crab, vulture, termites, wood beetle and crayfish. Also called scavengers.

FEEDING RELATIONSHIPS AMONG SPECIES

The Food Chain.

A food chain or food web comprises a sequence of organisms through which energy and nutrients are taken in and used up. A food chain in a wet meadow could be: Grass--> Grasshopper--> Snake--> Hyena.

Food chains begin from producers to consumers and the major feeding levels are called Trophic Levels.

Producers belong to the First Trophic Level. Primary consumers, whether feeding on living or dead producers feed from the Second Trophic Level. Organisms that feed on other consumers belong to the Third Tropic Level. Only about 10% of the calories in plant matter survive from First to the Second trophic level.

NON-FEEDING RELATIONSHIPS

1. Mutual relationships:

Relations between organisms can be

(a)     mutually beneficial to both species, For example, relationship between flowers and insects is a mutually supportive relationship, or …

(b)    Parasitic, in that such a relationship benefits only one party. Examples include ticks, fleas, mosquitoes, mistletoe plants and fungi.

Mutually beneficial relationships are also termed Symbiotic (sym = together, bio = living) and can be described as

a)        Commensalism is a mutual interaction between two different species in which one organism benefits but the other is neither harmed nor helped in any way, or…

b)        Mutualism is a type of species interaction in which both participating species benefit.

2. Competitive Relationships:

Plant and animal species compete over food, water, territorial space and mating with the opposite sex.

The Principle of Competitive Exclusion: explains that no two species can occupy the same niche (food or space) successfully in a stable community.

Closely related species therefore live far from one another. This is because plants and animals must compete for water, nutrients, light and space. The outcome of this competition determines the character of an ecosystem.

BIOGEOCHEMICAL CYCLES

Processes through which elements that sustain life (water, carbon, phosphorus and nitrogen) are continuously made available to living organisms.

Well known chemical cycles include:

a)         Nitrogen Cycle,

b)        Hydrological cycle,

c)         Carbon cycle, and …

d)        Phosphorus cycle

THE NATURAL BOIMES

1.         Equatorial and Tropical Rain Forest

a) evergreen broadleaf forest

2.         Tropical Seasonal Forest and Scrub

a) Tropical monsoon forest

b) Tropical deciduous forest

3.         Tropical Savanna

a) Tropical grassland b) Savanna woodland

4.         Mid-latitude Broadleaf and Mixed Forest

a) Temperate broadleaf

b) Midlatitude deciduous forest

5.         Needleleaf Forest & Montane Forest

a) Taiga, b) Boreal forest, Montane forest

6.         Temperate Rain Forest

a) West coast Forest, b) Coast redwoods

7.         Meditarranean Shrubland

a) Sclerophyllous shrubs

b) Australian eucalyptus forest

8.         Warm Desert and Semi-Desert

a) Subtropical desert and scrubland

9.         Cold Desert and Semi-Desert

a) Midlatitude desert, scrubland and steppe

10.  Arctic and Alpine a) Tundra