4.1 Evolution Produces Species Diversity
Natural selection acting on spontaneous mutations results in evolution
All species have environmental tolerance limits
Taxonomy describes relationships between species
Natural Selection leads to evolution
 Adaptation: the acquisition of traits that allow a species to survive in its
environment
o Most important concept in biology
 Adapt is used it 2 ways:
o 1. An individual organism can respond immediately to a changing
environment in a process called acclimation
 Ex.
o 2. Another type of adaptation affects populations consisting of many
individuals
 Ex. Genetic traits are passed from generation to generation
and allow a species to live more successfully in its environment
 Evolution: species change over generations because individuals compete
for scarce resources
 Natural Selection: the passing on of the better selected individuals traits to
their offspring or next generation
o The new traits are encoded in the species DNA
 Every organism has an array of genetic diversity in its DNA
 Mutations: changes to the DNA coding sequence of individuals
o The changed sequences are often inherited by offspring
o Main causes for mutations:
 Exposure to ionizing radiation & toxic materials
 Random recombination & mistakes in replication of DNA
during reproduction
 Evolutionary change: mostly brought about many mutations accumulating
over time
 Selection Pressures: the result in a species population that differs from
those of numerous preceding generations
All species live within limits
 Environmental factors: exert selection pressure & influence the fitness of
individuals & their offspring
o Because of this species are limited in where they can live
 Limiting factors:
o 1. Physiological stress due to inappropriate levels of some critical
environmental factor, such as moisture, light, temperature, pH or
specific nutrients
o 2. Competition with other species
o 3. Predation, parasitism & disease
o 4. And LUCK
 For example when an individual organism find their way to a
new habitat and start a new population is simply luck rather
than they are more fit
 An organisms physiology and behavior allow it to survive only in CERTAIN
environments
 There must be certain factors at certain levels in order for the organism to
survive
 Critical factor: (the single factor in shortest supply relative to demand)
Chemist Justus von Liebig found this out
o Ex. The giant saguaro cactus
 Later ecologist Victor Shelford expanded Liebig by stating that each
environmental factor has both minimum & maximum levels called
TOLERANCE LIMITS beyond which an a particular species cannot survive or
is unable to reproduce
 The single factor closest to survival limits is the critical factor that limits
where a particular organism can live
 Indicators: the requirements and tolerances of specific environmental
characteristics
o The presence or absence of species indicates something about the
community & the ecosystem as a whole
The ecological niche is a species’ role and environment
 Habitat: place or set of environmental conditions in which a particular
organism lives
 Ecological niche: the role played by a species in a biological community &
the set of environmental factors that determine its distribution
o Niche first defined by ecologist Charles Elton
 To Elton each species has a role in a community of species &
the niche defined its way of getting food, the relationship it
had with other species, and the services it provided to its
community
o 30 years later G.E Hutchinson proposed a more physical and
biological definition of the word niche
 Every species exists within a range of physical and chemical
conditions, (temperature, light levels, acidity, humidity, &
salinity
 Also exists within a set of biological interactions such as the
presence of predators or prey, or the availability of nutritional
resources
 Generalists: species who tolerate a wide range of conditions or exploit a
wide range of resources
o They have large geographic ranges
 Specialists: species who have a narrow ecological niche (do not tolerate
environmental change well)
o Ex. Panda
 Endemic species: (most often specialists) they occur only in one area or
one type of environment
 In most organisms their genetic traits and instinctive behaviors restrict their
ecological niche
 The principle of competitive exclusion: no 2 species can occupy the same
ecological niche for long
o The species that is more efficient in using available resources will
exclude the other
 Resource partitioning: when species disappear or develop a new niche,
exploiting resources differently
o Partitioning can also allow several species to utilize different parts of
the same resource and coexist within a single habitat
o Resources can be partitioned in time as well as space
 Ex.
Speciation maintains species diversity
 As population becomes more adapted to its ecological niche it may develop
specialized or distinctive traits that eventually differentiate it entirely from
its biological cousins
 Speciation: development of a new species
 Geographic isolation:
 Allopatric speciation: speciation that occurs when populations are
geographically separated
 Behavioral isolation:
 Sympatric speciation: speciation that occurs within one geographic area
o Ex.
 Directional slection:
o Ex. can be observed in the emergence of antibiotic- resistant bacteria
 Stabilizing selection: reduce variation in a trait
 Disruptive selection: can cause traits to diverge to the extremes
 New environmental conditions lead to speciation as new opportunities
become available
 Geological time is marked by periods of tremendous diversification that
have followed the sudden extinctions of species
Taxonomy describes relationships among species
 Taxonomy: the study of types of organisms and their relationships
o With it you can trace how organisms have descended from common
ancestors
 Taxonomic relationships among species are displayed like a family tree
 Binomials: they identify and describe species using Latin nouns and
adjectives or names of peoples or places
o Scientists communicate about species using these scientific names
rather than their common names
 Taxonomy also helps describe specimens and subjects in museum
collections & research
 Scientists recognize six kingdoms:
o Animals
o Plants
o Fungi
o Protists
o Bacteria
o And archaebacteria
 Within these kingdoms are millions of different species
4.2 Species Interactions shape biological communities
Competition leads to resource allocation
Predation is an important type of selective pressure
Symbiosis benefits both species involved
Competition leads to resource allocation
 Intraspecific competition: competition among members of the same
species
 Interspecific competition: competition between members of different
species for resources
 Competition shapes species population and biological communities by
causing individuals and species to shift their focus from one segment of a
resource type of another
 Ways to reduce competition in a species population
o The young of the year disperse
 Seeds being carried elsewhere by the wind
o Exhibiting strong territoriality
 Ex. Many animals force their offspring and competing adults
from their vicinity
 This minimizes competition between individuals and
generations
o Resource partitioning between generations
 Ex. Adults and juveniles of this region occupy different
ecological niches
 Many animals try to avoid fighting for resources and instead confront each
other with noise and movements
 Each species has its tolerance limits for abiotic (non-living) factors
 Studies show that when two species compete 2 species compete the 1
living in the middle of its tolerance limits has the advantage and usually
prevails in competition with other species living outside its environmental
conditions
Predation affects species relationships
 Predator: any organism that feeds directly on another living organism
o Whether or not it kills the prey (carnivores, herbivores, and
omnivores)
 Predation:
 Predation affects:
o All stages in the life cycle of predator and prey species
o Many specialized food-obtaining mechanism
o The evolutionary adjustments in behavior and body characteristics
that help prey avoid being eaten and help predators find food more
easily
 Predator-mediated competition: in this a superior competitor in a habit
builds up a larger population than the competing species
o Allows weaker competitors to increase their numbers
 Predatory relationships may change as the life stage of an organism
changes
o Ex. (page 84)
Some adaptations help avoid predation
 Coevolution: the response of predator to prey and vice versa over
thousands of years produces physical and behavioral changes in this
process
o Can be mutually beneficial
 Batesian mimicry: certain species that are harmless resemble poisonous or
harmful ones to keep predators away
 Mullerian mimicry: involves 2 unpalatable or dangerous species who look
alike
o When predators learn to stay away from that species they both
benefit
Symbiosis involves intimate relations among species
 Symbiosis: two or more species live intimately together with their fates
linked
o These types of relationships often enhance the survival of one or
both partners
 Mutualism: when organisms combine to mutually benefit
 Commensalism: a type of symbiosis in which one member clearly benefits
and the other is neither benefited or harmed
 Paratism: a form of predation
o Can also be considered symbiosis because dependency of parasite on
host
 Mutualistic relationships often entail some degree of coevolution where
partners change together
o Ex. Moths
Keystone species have disproportionate influence
 Keystone species: plays critical role in a biological community that is out of
proportion to its abundance
o Keystone species tend to be more common in aquatic habits than in
terrestrial ones
4.3 Community Properties Affect Species and Populations
 Productivity is a measure of biological activity
 Abundance and diversity measure the number and variety of organisms
 Resilience and stability make communities resistant to disturbance
Productivity is a measure of biological activity
 Primary productivity: a communities rate of biomass production
o An indication of the rate of solar energy conversion to chemical
energy
 Net primary production: the energy left after respiration
 Light levels, temperature, moisture, and nutrient availability help regulate
PHOTOSYNTHETIC RATES
 Only a small percentage of the available sunlight is captured and used to
make energy-rich compounds
o Only 0.1 to 0.2% of the absorbed energy is used by chloroplasts to
synthesize carbohydrates
Abundance and diversity measure the number and variety of organisms
 Abundance: an expression of the total number of organism in a biological
community
 Diversity: a measure of the number of DIFFERENT species, ecological
niches, or genetic variation present
 The abundance of a particular species is often inversely related to the total
diversity of the community
o General rule- diversity decreases but abundance within species
increases as we go from the equator toward the poles
 Productivity is related to abundance and diversity because they are both
dependent on the total resource availability in an ecosystem as well as the
reliability of resources, the adaptations of the member species and the
interaction between species
 Ways a community may not be perfectly adapted to their environment:
o A new community who hasn’t had time for niche specialization
o A disturbed community where roles such as top predator are missing
Community structure is the spatial distribution of organisms
 Ecological structure: refers to patterns of spatial distribution of individuals
and populations within a community as well as the relation of a particular
community to its surroundings
 At local level, even in homogenous environments, individuals in a single
population can be distributed randomly or in highly regular patterns, or
clumped together
o In randomly arranged populations individuals live wherever
resources are available
o Ordered patterns may be determined by the physical environment
but are more often the result of biological competition
 Ex.
 Many aquatic communities are stratified into layers based on light
penetration in the water, temperature, salinity, pressure, and other factors
Complexity and Connectedness are important ecological indicators
 Community complexity and connectedness are related to diversity
o Important because they help us visualize and understand community
functions
 Complexity: refers to the number of species at each trophic level and the
number of trophic levels in a community
o A diverse community may not be very complex if all species are
clustered together in only a few trophic levels and form a relatively
simple food chain
o A complex, highly interconnected community might have many
trophic levels some of which can be compartmentalized into
subdivisions
Resilience and stability make communities resistant to disturbance
 Constancy: lack of fluctuations in compositions or functions
 Inertia: resistance to perturbations
 Renewal: ability to repair damage after disturbance
Edges and boundaries are the interfaces between adjacent communities
 The boundary between one habitat and its neighbors is an important
aspect of community structure…these relationships are called EDGE
EFFECTS
 Ecotones: the boundaries between adjacent communities
 Community that is sharply divided from its neighbors is called a closed
community
 Open communities: gradual or indistinct boundaries over which many
species cross
4.4 Communities are dynamic and change over time
 Some biological communities are dependent on periodic disturbance
 Introduced species can cause profound community change
The nature of communities is debated
 Communities develop in a series of stages
o Starting either from bare rock or after a severe disturbance
 Climax community: species replace each other in predictable groups and in
a fixed, regular order
o Maximum complexity and stability that was possible
Ecological succession is the history of community development
 Primary succession: land that is bare of soil is colonized by living organisms
where none lived before
 Secondary succession: when an existing community is disturbed a new one
develops from the biological legacy of the old
o In both successions organisms change the environment by modifying
soil, light levels, food supplies, and microclimate
 Ecological development or facilitation: This change permits new species to
colonize and eventually replace the previous species
 Pioneer species: (microbes, mosses, and lichens) that can withstand a harsh
environment with few resources
o When they die the bodies of pioneer species create patches of
organic matter
 As succession continues, the community now becomes more diverse and
interspecies competition arises
 Pioneer species disappear as the environment favors new colonizers that
have competitive abilities more suited to the new environment
 Secondary succession is all around us
o In abandoned farms
o Clear cut forests
o & in disturbed suburbs or lots
 Generalists figure prominently in early succession
 Long periods of community development lead to greater community
complexity, high nutrient conservation and recycling, stable productivity, &
great resistance to disturbance
Appropriate disturbances can benefit communities
 Disturbance: any force that disrupts the established patterns of species
diversity and abundance, community structure, or community properties
o Animals can causes disturbance
 Ex. Elephants
 Aboriginal populations have disturbed and continue to disturb communities
around the world
 Breaking the grip of a super-competitor is the helpful role disturbances
often play
 Disturbance-adapted species: landscapes that never reach a stable climax in
a traditional sense because they are characterized by periodic disturbances
and are made up of species DISTURBENCE ADAPTED SPECIES that survive
fires underground, or resist the flames, and then reseeds quickly
Introduces species can cause profound community change
 Succession requires the continual introduction of new community members
and the disappearance of previously existing species
o New species move in as conditions become suitable
o Other die or move out as the community changes
o New species can also be introduced after a stable community has
already become established
 If however an introduced species preys upon a or outcompetes one or
more of the populations living in that community the entire nature of the
community can be altered
 Prolific:
 Sometimes we introduce new species thinking it will make the problem we
are facing go away but in reality we are making it worse!!!!
o Ex. Mongoose on Hawaii