Final Stuff
Community Ecology
A biological community consists of interacting species, usually living within a defined area
Niche
The way an organism "uses" resources or the environment
- Space it uses
- Food it eats
- Environmental conditions
- Temperature, moisture, etc.
- Best mating conditions
Resource partitioning
Some lizards live on the ground, others in the crown of the tree, and others on the trunk of the same tree
Fundamental Niche
The niche an organism can survive in.
Full range of conditions & resources than an organism could theoretically use in the absence of competition with other species
Realized Niche
The actual niche an organism occupies.
Actual range of conditions and resources that an organism uses
Niche overlap between species leads to competition
Ecological Niche
Considers all abiotic factors such as pH, sunlight, moisture, salinity, and temperature
Selection plays a role in species interactions
Species Interactions
The realized niche will depend on these species interactions
Interactions affect the distribution & abundance of a particular species
Species act as agents of natural selection when they interact
Effects on fitness
(+) = positive effect
(-) = negative effect
0 = no net effect for individual
Species 1/Species 2
Predation
One organism eats another one
Parasitism
Benefits one species at the cost of the other
Competition
Lowers the fitness of all individuals involved either:
- Uses energy resources needed for survival & reproduction
- Death/injury
Interspecfic & Intraspecific
Mutualism
-/-
Competitive Exclusion Hypothesis
"competitors cannot co-exist"
Symmetric Competition
Same fitness
Asymmetric Competition
Varying fitness
Fitness trade-offs
No one organism is superior in all aspects of living. Could be good at competing for space, but less good at enduring droughts, disease, etc.
+/-
Herbivory
The consumption of plant tissues by herbivores
Predation
The killing & consumption of most or all of the prey individual by a predator
Natural selection favors traits that allow an individual to avoid being eaten
Safety in numbers
Fight back
Hide, run, fly or swim away
Mimicry
Müllerian
Looks dangerous, is dangerous
Batesian
Looks dangerous, isn't dangerous
+/-
Biologists use 2 hypotheses to help answer the question of why herbivores don't eat more of the food available
Bottom-up limitation hypothesis
Plants provide poor nutrition or are well-defended against herbivory
Competitive exclusion occurs when competition is asymmetric
Cryptic coloration
+/+
+/-
Parasite exerts selection in 2 ways:
- Appearance
- Behavior
Commensalism
One species benefits but the other is unaffected
- Flowering plants & pollinators
- Mycorrhizal fungi & plant roots
- Farmer ants & fungi
- Crematogaster ants & acacia trees
- Cleaner shrimp & fish
Top-down control hypothesis
Herbivore is limited by disease/predators
+/0
Co-evolution
Two species evolve in response to the pressure exerted by the other
The outcome of interactions among species is dynamic & conditional
Population Ecology
Group of individuals (of the same species) that live in the same place at the same time
Geographic distribution: Range
Ranges can undergo contractions and expansion
- Global
- Regional
- Local
Patchy distribution at regional & local scales
Distribution of organisms at the local scale:
Random, Uniform, Clumped
Uniform
Clumping
Sociality
Random
Competition will create a more uniform distribution
Territoriality (establishing & defending a territory) will create a more uniform distribution
Resource distribution
Resource distribution is usually not uniform, so neither is organism distribution
Predation
(safety in numbers; group avoidance)
Random distributions are rare
Demography
The study of the number of individuals in a population. It depends on:
- Birth
- Increase
- Immigration
- Increase
- Death
- Decrease
- Emigration
- Decrease
Population Growth
Growth = Change in N/Change in Time
= dN/dt
N is population size
r
r = per capita rate of increase
r = difference between birth & death
+r = more births than deaths
-r = more deaths than births
If r is positive, then the population is: increasing
If r is negative, then the population is: decreasing
Changes in population size result from 2 factors:
Density dependent
Depends on density
Logistic Growth
The population growth rate gets smaller & smaller as population reaches maximum & is limited by resources in the environment (carrying capacity)
Carrying Capacity
Maximum number of individuals that can be supported by the place
Density independent
Does not depend on density
Population size increases until it reaches a carrying capacity
Growth is often density dependent
When there is NO more space, the death rate > birth rate, r will decline
Exponential Growth
If r is positive and constant, the population will grow exponentially (no limit to how big a population can get)
Doesn't depend on the # of individuals in the population
Depends on the # of individuals in the population
If there are too many individuals, then death rate will increase faster than new individuals are born
Observed naturally in 2 circumstances:
- A few individuals found a new population in a new habitat
- A population has been devastated by a storm or some other type of catastrophe & then begins to recover, starting with a few surviving individuals
Ecologists use 3 ways to predict if a population will grow or shrink
Survivorship Curves
Graphs that show what fraction of a population survives from one age to the next
Age-sex pyramid
"Snapshot" of a population in time showing how its members are distributed among age and sex categories
Life Tables
Summarize birth and death rates for organisms at different stages of their lives
Fecundity
The # of female offspring produced by each female in the population
Age-specific Fecundity
The average # of female offspring produced by a female in a given age class (group of individuals of a specific age)
Human populations
Growth rates differ among regions of the world
Growth depends on the number of reproductive individuals
Every individual has a restricted amount of time & energy at its disposal (its resources are limited)
A female can maximize fecundity, maximize survival, or strike a balance between the 2
Experimental Manipulation of Trade-offs
- Presence of egg yolk (supplies nutrition)
- Number of competing eggs (more eggs = more competition)
Control - result: 'typical' medium size
1. yolk removed from egg - result: smaller offspring
2. eggs removed - result: larger offspring because there were more resources when siblings were removed
Balance between the number of offspring & the investment per offspring
Life History
Key components of life (reproduction & survival) are shaped by natural selection
How to produce the highest number of (surviving) offspring & survive
r & k selected species
- r-selected: mature in one season produces many young
- Mice, rabbits, bacteria
- k-selected: matures over several decades produces few young
- Birds, elephants, large mammals, coconut trees
Life History Adaptations
Adaptation --> r-selected --> k-selected
Age at first reproduction --> early --> late
Life span --> short --> long
Maturation time --> short --> long
Mortality rate --> often high --> usually low
Number of offspring produced per year --> many --> few
Number of reproductions per lifetime --> few --> many
Parental care --> none --> often extensive
Size of offspring or eggs --> small --> large
Survivorship Curves
Populations cycle in number (up, down, up, down)
Type I
Survivorship throughout life is high, and most individuals approach the maximum life span of the species
Humans have Type I curve
Type II
Most individuals experience relatively constant survivorship over time
Songbirds have Type II curve
Type III
High death rates early in life, with high survivorship after maturity
Many plants have this curve
Behavioral Ecology
Proximate Causation
Ultimate Causation
Mechanism
Mechanisms that are the reason for behavior
- Nervous system
- Hormones
- Genetics
Behavioral Ecology
Determines how behavior influences reproductive success or survival
- Reproductive strategies
- Altruism
- Group living & animal societies
Physiology
How behaviors are influenced by hormones, nerve cells & other internal factors
Phylogeny
Origin of a behavior in groups of related species
Adaptive Significance
Behavior's role in survival & fitness
Behavior and decision making
Innate Behavior
- Instinctive, doesn't require learning
- Preset paths in nervous system
- Genetic (fixed action pattern)
- Fixed Action Patterns: highly inflexible, stereotyped, behavior
- Ex: Goose rolling egg back to the nest
- Ex: Goose rolling egg back to the nest
- Fixed Action Patterns: highly inflexible, stereotyped, behavior
Ex: goose replacing an egg from her nest
Behavioral Genetics
Contribution that heredity makes to behavior
Nature: genes guide development of nervous system and potentially the behavioral responses
Nurture: animals may also develop into a rich social environment and have experiences that guide behavior
Artificial selection data has shown that behavioral differences among individuals result from genetic differences
Condition-dependent Behavior
- Innate behavior is relatively rare
- Usually, behavior changes in response to learning & shows flexibility, depending on the context
- In many cases, there is a range of actions (behavior) in response to a stimuli
"Cost-Benefit"
The link between condition-dependent behavior and fitness
- Animals weigh the cost & benefit of an action with respect to fitness
- What action will maximize the ability to produce offspring
5 questions in behavioral ecology
- What to eat
- Who to mate with
- Where to live
- How to communicate
- When to cooperate
Eating
Optimal foraging: animals maximize their feeding efficiency
- Risk of attack while eating
- How much energy is gained by eating
- How much energy it takes to eat & forage
Communicating
Signals must be received
Optimal foraging evolves through natural selection
Natural selection will favor behavior that maximizes energy acquisition if the increased energy reserves lead to increases in reproductive success
- Avoid predators while finding food
- Avoid predators while finding food
Optimal behavior has evolved by natural selection
- Female zebra finches that were successful foraging had successful offspring
- Removed offspring to ensure learning was not a part of the foraging success
Pheromones
Chemical messengers used for communication between individuals of the same species
- Sex attractant
- Males have sensory receptors
- Some insect pheromones can be detected as far as 7km away
Acoustic Signals
Vocal calls of amphibians/birds
Females are the choosy sex, and females prefer the complex call
Balance between signals that evolve under natural & sexual selection
Mating
How does sexual activity occur (hormonal occur)
Sex hormones increase during the breeding season
- Testosterone (males)
- Estradiol (females)
Deceitful signals are used in predation & mating
2 stimuli needed for hormonal changes to induce sexual behavior in females
- Breeding males
- Spring time
Cooperation
Altruism is flexible, condition-dependent behavior
Altruism: There is a fitness cost to the individual exhibiting the behavior, but a fitness gain to the recipient
Kin Selection
Evolutionary strategy that favors the reproductive success of an organism's relatives, even at a cost to the organism's own survival & reproduction
- Direct genetic advantage to altruism
- Natural selection will favor any behavior that increases the propagation of an individual's alleles
- Inclusive fitness (considers gene propagation through direct and indirect reproduction)
Alleles for altruistic behavior should rise in frequency when:
rB > c
Ex: Surrogate mothers would adopt related orphaned squirrel pups, but not unrelated organs in squirrels
r = coefficient of relatedness
B = reproductive benefit to recipient
c = reproductive cost to actor
Reciprocal Altruism: altruistic behavior among non-related individuals
Example
Surrogate mothers would adopt related orphaned squirrel pups, but not unrelated organs in squirrels
B = measured as the increased chance of survival of the orphan
c = calculated by measuring a decrease in the survival probability of the entire litter after increasing the litter by 1 pup
rB was greater than C - Females always adopted orphans
when rB was less than C - Females never adopted
Living
Habitat Selection
- Juveniles disperse from natal ground
- How large a territory should be defended?
- How do habitat density & quality affect fitness?
Territorial behavior secures resources
- Home range: where the animal lives & forages; defends territory
- Defense against intrusion by other individuals
- Birds sing/display to signal their territory; energetically costly
- Benefit: increased food intake, access to mates, or access to refugees from predators
Migration & Navigation
Orientation: follow a bearing (route from one place to another)
Navigation: adjust or set a bearing using stars, sun, magnetic field
Homing experiments show that birds can find their nest after being displaced
True for other animals
Zero Growth
Negative Growth
Rapid Growth
