I.
Chapter 5: Biodiversity, Species Interactions, and Population Control
a. 5-1: How Do Species Interact?
i. Five basic interactions among species:
1. Interspecific Competition – most common interaction, occurs when members
of two or more species interact to use the same limited resources such as
food, water, light, and space
a. Most interspecific competition involves the ability of one species to
become more efficient than another species in obtaining the resources
it needs.
i. When two species compete with one another for the same
resource their niche overlaps. The greater the overlap, the
more intense their competition for key resources is.
1. Humans compete with many other species for space,
food, and other resources
b. Resource Partitioning – populations of some species develop
adaptations that allow them to reduce or avoid competition with
other species for resources.
i. Competing for similar scarce resources evolve specialized
traits that allow them to share resources by using parts of
them, using them at different times, or using them in different
ways.
2. Predation – a member of one species (the predator) feeds directly on all or
part of a living organism (the prey) as part of a food web.
a. Predator-Prey relationship
b. Predator’s have a variety of methods that help them to capture prey.
i. Pursuit and Ambush
ii. Camouflage
iii. Chemical Warfare
iv. Prey Species – adaptations include protective shells, thick bark,
thorns, spines
v. Mimicry – gain protection by looking and acting like other,
more dangerous species, a protective device
vi. Echolocation – navigate and locate their prey
c. Population level – predation plays a role in evolution by natural
selection
i. Predator and prey can exert intense natural selection
pressures on one another
d. Coevolution – two different species interact in such a way over a long
period of time, changes in the gene pool of one species can lead to
changes in the gene pool of the other
3. Parasitism – Occurs when one species (the parasite) feeds on another
organisms (the host), usually by living on or inside the host
a. Host point of view, parasites are harmful
b. Population perspective, parasites can promote biodiversity by helping
to keep the populations of their host in check
4. Mutualism – Two species behave in ways that benefit both by providing each
with food, shelter, or some other resource
a. In reality, the species in a mutualistic interaction benefit one another
unintentionally and are in it for themselves
5. Commensalism – an interaction that benefits one species but has little, if any,
beneficial or harmful effect on the other.
b. 5-2: How do Communities and Ecosystems Respond to Changing Environmental
Conditions?
i. Ecological Succession – types and numbers of species in biological communities and
ecosystems change in response to changing environmental conditions such as fires,
volcanic eruptions, climate change, and the clearing of forests to plant crops.
1. Primary Ecological Succession – involves gradual establishment of
communities of different species in lifeless areas where there is no soil in a
terrestrial ecosystem or no bottom sediment in an aquatic ecosystem.
2. Secondary Ecological Succession – which a series of communities or
ecosystems with different species develop in places containing soil or bottom
sediment.
3. Ecological Succession is an important ecosystem service that tends to
increase the biodiversity of communities and ecosystems by increasing
species richness and interactions among species.
a. Both primary and secondary ecological succession are example of
natural ecological restoration
i. Three factors that affect how and at what rate succession
occurs:
1. Facilitation – which one set of species makes an area
suitable for species with different niche requirements,
and often less suitable for itself.
2. Inhibition – which some species hinder the
establishment and growth of other species
3. Tolerance – which plants in the late stages of succession
succeed because they are not in direct competition with
other plants for key resources.
b. Traditional view – ecological succession proceeds in an orderly
sequence along an expected path until a certain stable type of climax
community occupies an area
c. Ecological succession reflects the ongoing struggle by different
species for enough light, water, nutrients, food, space, and other key
resources.
ii. Stability or capacity to withstand external stress and disturbance, is maintained
only by constant change in response to changing environmental conditions.
1. Two aspects of stability or sustainability in living systems:
a. Inertia (Persistence) – the ability of a living system such as a
grassland or a forest to survive moderate disturbances
b. Resilience – the ability of a living terrestrials system to be restored
through secondary ecological succession after a more severe
disturbance
i. Evidence suggest that some ecosystems have one of these
properties but not the other
c. 5-3: What Limits the Growth of Populations?
i. Population – a group of interbreeding individuals of the same species.
1. Three ways in which the members of a population are typically distributed or
dispersed.
ii.
iii.
iv.
v.
vi.
vii.
a. Clumps (most populations live like this)
i. The resources a species needs vary greatly in availability from
place to place
ii. Individuals moving in groups have a better chance of
encountering patches or clumps of resources
iii. Living in groups provides some protection from predators
iv. Living in packs gives some predator species a better change of
getting a meal
2. Births, deaths, immigration, and emigration govern changes in population
size
a. Population Change = (Births + Immigration) – (Deaths + Emigration)
Age Structure – the distribution of individuals among various age groups
1. Usually described in terms of organisms not mature enough to reproduce
(the prereproductive stage), those capable or reproduction (the reproduction
stage), and those too old to reproduce (the postreproductive stage).
Range of Tolerance – Variations in its physical and chemical environment
Limiting Factors – more important than other factors in regular population growth
1. Limiting Factor Principal – too much or too little of any physical or chemical
factor can limit or prevent the growth of a population, even if all other factors
are at or near the optimal range or tolerance
a. On land, precipitation often is the limiting factor
b. Aquatic life zones – includes temperature, sunlight, nutrient
availability, acidity, and the low levels of oxygen gas in the water
i. Salinity – the amounts of various inorganic minerals or salts
dissolved in a given volume of water.
Population Density – The number of individuals in a population found within a
defined area or volume
Different reproductive patterns help to ensure the long-term survival of species
1. No population of a species can grow indefinitely because of limitations on
resources and competition with populations of other species for those
resources
a. There are always limits to population growth in nature
Environmental Resistance – the combination of all factors that act to limit the
growth of a population.
1. Carrying Capacity – the maximum population of a given species that a
particular habitat can sustain indefinitely
a. A population with few, in any, limitations on its resource supplies can
grow exponentially at a fixed rate or percentage per year.
b. Plotting the number of individuals against time yields a J-shapes
growth curve
c. Exponential Growth – occurs when a population has essentially
unlimited resources to support its growth
i. Eventually converted to logistic growth, which the growth rate
decreases as the population becomes larger and faces
environmental resistance
d. Population size typically stabilizes on or near the carrying capacity
which results in a sigmond (S-shaped) population growth curve
e. The carrying capacity can vary over time due to changing conditions
viii. Population Crash (Dieback)– when a population overshoots or exceeds the carrying
capacity of their environment.
ix. The carrying capacity of any given area is not fixed
1. It can rise or decline seasonally and from year to year
2. Humans are not exempt from population crashes
a. Bubonic Plague
b. Global Epidemic of AIDS
i. So far, technological, social, and other cultural changes have
expanded the earth’s carrying capacity for the human species.