Unit 1: Sustainability of Ecosystems
1.1 Biotic and Abiotic Factors in Ecosystems: (sec 2.1 pg 21-24)
 The study of how organisms interact with each other and with their physical environment is
called ecology.
The environment is divided into different levels.
Level 1:organism = single living thing.
Level 2:population = all of the organisms of the same species that share a habitat.
Level 3:community = all of the different populations in a particular area that interact.
Level 4:ecosystem = includes the living community as well as the physical environment in
which the organisms live
Level 5:Biosphere = is the total area of Earth where living things are found.
 Each environment has two kinds of factors:
o Abiotic = nonliving factors
o Biotic = living factors
 A limiting factor is the most critical factor in determining the types of organisms that exist
in an ecosystem. Many organisms compete for the same limiting factor(s).
 Many ecosystems are in a state of dynamic equilibrium, where there is a balance between
the abiotic and biotic factors and their connection to each other, but there is also continuous
change. Most ecosystems experience continuous change, but the overall system is still
stable.
1.2 Ecological Roles and Relationships/Symbiosis: (sec 2.2 and 2.3 pg 25-32)
 The organisms in each ecosystem have different roles.
 Producers or autotrophs = are organisms that make their own food (usually through
photosynthesis).
o plants are producers on land (trees, shrubs, grasses, flowers, etc.)
o algae are producers in aquatic environments (including seaweeds, and also
phytoplankton - which are microscopic algae)
 Consumers or heterotrophs = organisms that consume other organisms or biotic waste in
order to survive. (Note different groups of consumers listed below and in Fig.2 pg.26)
o Herbivores or primary consumers = consumers that eat producers.
o Carnivores = consumers that eat other consumers (primary and secondary).
o Omnivores = consumers that eat both producers and other consumers.
o Detrivores= consumer organisms that feeds on the waste material in an ecosystem,
including dead organisms, plant debris and animal feces (Fig.5 pg.27)
o Decomposers = consumer that breaks down the complex molecules found in dead
organisms into simpler molecules by process of biodegredation. VERY important in
ecosystem – lots of invertebrates (e.g. worms and insects), bacteria and fungi. They
make the nutrients available to producers by putting it in the soil (Fig 6 pg.27)
o Predator = an organism that actively hunts another organism and kills it for food.
o Prey = an organism hunted by another organism.
o Predator – Prey cycle = the population cycles that predators and preys go through
(constantly fluctuating). Cycle begins when prey population decreases as preds eat
prey; then predator population decreases because of reduced food available; then prey
population bounces back because of fewer predators. Lynx-snowshoe hare
relationship in Northern Canada well-studied (see. Figs 8&9 pg.28).
o In natural populations, there can be many other environmental factors that affect
abundance of organisms (e.g. drought affects plants affects herbivores affects.....)
 There are different types of relationships between organisms. Symbiosisrefers to any close
relationship between different species(often called a symbiotic relationship), including:
 Mutualism = a relationship in which both species obtain some benefit from the interaction
(e.g. lichen Fig 1 pg.30).
 Commensalism = an interaction in which one organism benefits while the other is
unaffected. (e.g. whale/barnacle Fig.2 pg. 30; some biologists argue this doesn’t exist...)
 Parasitism = when one organism lives and feeds on, or in, the body of another organism
called the host.Parasite benefits, host is harmed. Parasites can have a positive role in
ecosystem, as they can control species’ population growth and over-abundance (may ensure
strongest and healthiest members survive).
 Biologists estimate up to 25% of all animal species may be parasites!
 Plant parasites exist too (Fig 4 pg.31) – they steal nutrients from the host instead of through
photosynthesis
1.3 Trophic Levels and Energy Flow (Sec 2.4 pg 33-37)
 As one organism eats another, nutrients and energy move through the ecosystem, passing
from producers to consumers (see Fig.1 pg 33).
 The nutrients are recycled through the process of biodegradation but the energy only moves
in one direction through the community.
 A trophic level describes the position of the organism in relation to what it eats and what
eats it, in the ecosystem:
1st level = this is all producers
2nd level = this is all herbivores
3rd level = this is carnivores and omnivores.
 note decomposers play a unique role – they consume material from ALL other
levels, so they could be shown in all trophic levels.
Food Web
 A food chain is the pathway that energy
and nutrients take through the trophic
levels. The organism that is eaten is
connected by an arrow to the organism that
eats it. Note the terms we use in a food
chain, including producer, primary
consumer, secondary consumer, tertiary
consumer, and decomposer. Food chains
highlight individual interactions between
consumer levels.
 Check out detritus food chain Fig.4 p.35
 A food web is a collection of the different
food chains in an ecosystem, and represents
a more realistic (and complicated) model of
how energy and nutrients pass through
ecosystems.
1.4 Ecological Pyramids (Sec 2.5 pg 39-41)
 We can represent the pathways that energy takes through an ecosystem with an ecological
pyramid (a.k.a. food pyramid). There are three types; all have producers on the bottom,
then primary consumers, then secondary& tertiary consumers.
o Pyramid of Energy = each level represent the amount of energy available to the nest
level. Only about 10% of the energy of each level is passed on to the next!
o most energy at any level used for basic life processes (movement, reproduction, etc.)
o Pyramid of numbers = each level represents the actual number of individuals in that
trophic level.
o Shapes vary widely depending on the physical
size of producers (e.g. grasslands have LOTS
of individual grasses; mature forests have
much fewer large trees)
o Pyramid of mass = each level
represents the total mass of the
organisms in that trophic level.
o Most communities have the standard
shape shown here (there is a consistent
pattern to the biomass at each level
across most communities)