CHAPTER 2. EVOLUTIONARY ECOLOGY
Evolutionary ecology studies the evolution in populations of organisms. It is questioned if different phenotypes lead
to differences in biological efficacy and how that affects the distribution of phenotypes in the following generations.
1) CONCEPT OF ADAPTATION AND ACCLIMATION
Adaptation: the process of change by which an organism or species becomes better suited to its environment. This is
an evolutionary process so it is permanent and takes long time.
Acclimation: is a form of adaptation that an organism undergoes when transferred to a different habitat. It doesn’t
take as long as evolutionary adaptation and it doesn’t affect the body composition of the entire species. Adjustment
is made by modifying physical reactions to environmental changes, like shivering when exposed to cold weather. This
process is temporary.
High altitude plants are better adapted to frost days than tropical plants. Correct
High altitude plants reduce their adaptation to cold during summer and re adapt again over winter. It’s
incorrect because and adaption can not be changed in a short period of time
After treating corn plants with heavy shade for 1 month, these adapted to the lack of light increasing their
chlorophyll concentration. Incorrect, it isn’t an adaptation, it’s an acclimation.
Since antibiotics are used in medicine, a number of bacteria have antibiotics that have acclimated, gaining
resistances. Incorrect
Humans are adapted to summer’s high UV-B radiation. They acclimate by increasing the melanine
concentration in the epidermis after exposition to UV-B. Correct.
2) CONCEPT OF FITNESS
The fitness of an individual animal is a measure of its ability, relative to others, to leave viable offspring. The fittest
individual is not necessarily the strongest, fastest, or biggest. A genotype's fitness includes its ability to survive, find a
mate, produce offspring and ultimately leave its genes in the next generation.
Biologists have long worked in evolutionary processes and they
have been able to demostrate the adaptation of a big poblation.
In 1976, before the drought the birds had small beaks, some had
medium sized beaks, and others had large beaks
In 1978, after the extremely drought, smaller and larger beaks
being more common.
The ecological explanation for this outcome was that the drought
resulted in a less food for the finches, which led to a large
proportion of the population dying of starvation. However,
proportionally more large hard seeds were produced than small
soft seeds, and birds with larger beaks were better able to crack
these open than birds with smaller beaks. Thus, birds with larger
beaks had a selective advantage, even if a large proportion of
these still died. So, the size of the beaks got bigger, there was a
increase in the average size of the trait.
Evolution can act on behaviour traits, morphological traits, physiological traits, anatomical traits, etc.
3) WHAT IS BIOLOGICAL EVOLUTION?
Evolution is the change on the genetic composition of populations (proportion of genotypes). The evolution of a
population entails the diversification of organisms with time.
Microevolution: Change of populations of a given species throughout time (shorter time scales)
Macroevolution: Change of species throughout time (longer time scales).
Don’t confuse with speciation! Speciation is the fact that two isolated populations of a same species transform to two
different species. Microevolution is all about how it does people differs from each others. The speciation can be
considered as the link between microevolution and macroevolution.
4) DRIVERS OF EVOLUTION
If we exclude dispersion and mutation, the main drivers of population evolution are:
Natural selection: some genotypes get selected over others due to differences in survival, growth and
reproduction (the phenotypes expressed are selected) (individuals show differences in FITNESS in any given
environment).
Sexual selection: some genotypes get selected over others due to differences in ACCESS to reproduction (the
phenotypes expressed are selected).
The consequences of the two processes is that individuals in a population vary in the number of viable offspring they
produce from one population to the next.
Both types of selection (natural and sexual) affect the phenotype of individuals but the consequences affect the
proportion of genotypes in the population.
Genetic drift: is a mechanism of evolution in which allele frequencies of a population change over generations
due to chance (randomly).
The three drivers of evolution can act at the same time.
5) REQUIREMENTS FOR EVOLUTION BY NATURAL SELECTION
There must be genetic variation in the population for that trait
Can you have evolution in clonal populations?
Variation is a precondition to selection: without genetic variation there can be neither selection nor evolution.
The population must produce more descendents that can survive (leads to competition) (Difficult to see
evolution by natural selection in a decreasing population)
The best adapted individuals (a given trait value) leave proportionally more offspring alive and with
reproductive capacity than the rest (we say that the “selected individuals” have “higher fitness”)
Genetic variation for a given trait must be heritable: How do we measure heritability?
Traits with high heritability: body size, cream content in milk, egg weight, start date egg laying
Traits with low heritability: fecundity: nº offspring
6) UNITS OVER WHICH NATURAL SELECTION ACTS (DIFFERENT TO INDIVIDUAL)
Gametes: Gametic selection
Ej: sperm, pollen grain
Family groups: altruistic behaviour is driven by kin selection (suggested to explain altruistic behaviours in
family groups)
It’s contradictory with theory evolution because it was not focusing on an individual competing with others
to have more offspring.
The actor (giver) increases its fitness significatively
The actor (giver) incurs low costs
The actor (giver) and receptor (benefited) are kin: I will help who can help me in the future
Fitness = direct fitness + indirect fitness (The organism's genetic success is believed to be derived from
cooperation and altruistic behaviour)
Group selection: no close family ties
The population “uncountiously” maintains a consesus not to reach maximum reproductive potential and
hence avoid competition for resources.
7) SEXUAL SELECTION
Selective process (deterministic), responsable for the evolution of some traits, given the advantage of some individuals
exclusively in relation to their access to reproduction (mating).
- In dioecious species females tend to invest more in reproduction than males.
- Thus, female reproductive success (offspring alive for the next generation) is limited by their capacity to
produce eggs (and care for the offspring)
- Male reproductive success is determined by the total number of eggs they can fertilize, given that male
gametes are much cheaper to produce: CONFLICT OF INTERESTS, sexes have different strategies (priorities) to
maximize their reproductive success.
Consequence: females tend to be more selective when mating to get the maximum quality possible for their offspring
mating with and “adequate” male, whilst males compete for mating with as many females as possible.
Sometimes the roles are inverted and it is the males the ones that are selective, and the females the ones that compete
for males: IT ALL DEPENDS ON WHO MAKES THE HIGHEST REPRODUCTIVE EFFORT.
Intersexual: males compete selection to attract the female’s attention: she actively chooses her mate
Intrasexual selection: the female allows the winner of a combat or contest mate with her or the male that is
a better resource provider.
In some species, intrasexual selection happens not just before copulation: SPERM (competitive process
between spermatozoa of two or more different males to fertilize the same egg during sexual reproduction)
and INFANTICIDE (killing of young offspring by a mature animal of the same species so that the female can be
able to reproduce faster with the winner)
There can be conflicts between sexual and natural selection… However, often sexual selection entails selection for
individuals of higher genetic quality / higher overall fitness.
8) CONCEPT OF GENETIC DRIFT OR SAMPLING ERROR AND THE FOUNDER EFFECT
Topics to prepare for the scientific poster in the seminar session
o What is genetic drift?
o When does it happen and when is relevant for populations?
o What is the founder effect?
o Consequences for conservation and population viability
9) CONCEPT OF ECOTYPE
Population within a species which is genotypically adapted to specific environmental conditions.
10) APPLICATIONS OF EVOLUTIONARY ECOLOGY
Manage populations for increased reproductive success
Manage populations for desired sex ratios
Manage populations for desired trophy sizes
To understand the consequences of invasive species
RESUMEN:
What are the requirements for a population to evolve?
- Genetic variation: we need mutations, without mutation there wouldn’t be genetic variation, and without
variation there would be no evolution. Natural selection acts directly only on phenotypes, more genetic
variation within a population usually enables more phenotypic variation, and environment can act on this.
- Selection: after genetic variation, selection can act on this population. It’s a competition between
individuals leading to a better performance of some groups and worst performance from others.
- Migration or gene flow is a very important source of genetic variation because gene comes to a population
where those gene previously didn’t exist.
- Genetic drift: it’s the other main force. In each generation, some individuals, just by chance, leave
behind a few more descendents (and genes, of course) than other individuals. The genes of the next
generation will be the genes of the "lucky" individuals, not necessarily the healthier or "better"
individuals.
There is a lack of understanding of what evolution is.
People in general think that evolutionary time scales are long and ecological time scales are short. People thought that
if you look at species in the environment we can no see them change.
There was a dichotomy between genetics and ecologists that disappeared when they realized that evolution takes
place in short time scales as well.
The Breeder’s ecuation is a good way to see what evolution works but it’s not ideal for predicting evolutionary changes
in natural populations, it goes generation by generation which is very limiting because when we think about evolution,
we think about hundreds or thousands generations.
If we study evolution or we study cuantitative genetics we need to know what the ecological pressure is.
The R is the response to selection. It can refer a response in a morphological trait, in a physiological trait, etc.
When response is 0 (heritability or selection is 0) means that after many generations the trait does not change.
The breeders select two parents that have beneficial traits to reproduce (artificial selection). They can select:
- Morphological traits heavier individuals
- Physiological traits number of eggs, milk production
- Life-history traits the time they start to breed, when they die, when they stop growing…
- Behaviour traits loud call in birds
A physiological trait, like the total number of eggs or the total offspring of an individual, involve behavior because that
individual must found a mate.
h is heritability: the ability to transmit the information of your phenotype to your offspring. You need to have
heritability in that trait.
The proportion of the phenotypic variation in a quantitative trait in a population that is attributable to genetic variation
(differences in genotype).
If we have heritability for a trait there is a positive relationship between the value of the trait in the parents and the
value of the trait in the offspring.
S is selection, that can be measured in many ways but here it’s focus in the measure of the phenotype. Selection can
be the selection of the breeder, the natural selection (to survive) or the sexual selection (compete with others of the
same specie in order to reproduce).
Now we know how evolution works through natural selection. You know that natural selection in reality, at the end of
the day, is about the total number of copies that individuals leave. The number of copies that individuals leave must
be stronger related with survival, the time they live.
Evolution occurs in direction of response the trait when there is heritability and selection. If selection is positive, after
negative and so on we don’t have evolution.
Traits may be linked with treads-off.
A trade-off exists when one trait cannot increase without a decrease in another. One trait increase performance
(fitness) while decreasing performance in another.
For example, being big gives you some advantages in life but being big means you need more food and present a bigger
target to predators. Being small means that you don't need much food and can hide easily but it makes it easier for
another animal to eat you.
Genetic correlations can be either positive or negative, which reflects the direction of the relationship between the
two traits. A negative genetic correlation indicates that as one trait increases, the other trait tends to decrease. For
example, individuals that in general invest more in reproduction tends to invest less on somatic grotwh or immune
defense.
A trade-off occurs when an organism wants to do two different things, but has a limited amount of some important
resource. The resource could be time, calories, vital nutrients, or many other things. A simple example from everyday
life would be trying to buy both a television and a bike with a limited amount of money. You can’t afford an expensive
television AND an expensive bike. You would ideally want both an expensive bike and an expensive television, but you
are limited by a resource: money.
Trade-offs in biology work similarly, but often the mechanism or the
resource are not fully understood. To biologists, this often takes the
form of the observation that species rarely exhibit ‘perfect’
combinations of traits that are evolutionarily important, such as
lifespan and reproductive rate. Some species, such as elephants, are
very long lived, but reproduce very slowly. Other species, such as
mice, reproduce extremely rapidly, but are also short-lived. An ideal
combination from an evolutionary perspective would be to live a
very long time and also have lots of kids really fast. Nevertheless,
this is rarely seen in nature.
There are many examples of traits that are similar involved in trade-offs, such as brain size, muscle strength, and
growth rate. Essentially, any trait that is important in fitness but requires some limited resource will likely exhibit
trade-offs.
0
