Eco/Evo Exam 3

Population Size

measure the number of individuals in a population at a given time

Population density

The number of individuals of a population in a certain space at a given time

Population dispersion

the spatial pattern in which the members of a population are found in their habitat.

Clumped Dispersal

(MOST COMMON) Resources are usually patchy in nature. Additionally, some animal species form grazing herds, schools of fish, flocks of birds, and troops of primates to protect against predators, during migration, during mating season, or because they are social animals

Uniform Dispersal

(RARE) occurs mostly when individuals of the same species compete for resources that are scarce or when a species defends its territory by physical or chemical means. Example, Creosote bush in the desert biome. It competes for water (limiting factor) by excreting toxic chemicals that prevent seedlings of other creosote bushes from growing near it

Random Dispersal

(RARE) occurs when resources or conditions in the environment are fairly uniform and competition is limited. This condition is rare because environments are rarely uniform. Random dispersion is most common in weedy species that have a broad tolerance range for environmental conditions (‘generalists”)

Pre-reproductive age range

0-14

Reproductive age range

15-44

post-reproductive age

45-80+

Population momentum

pre-reproductive category has a high potential for growth

Environmental resistance

limits the growth of a population when all of the limiting factors in the environment work synergistically

Carrying capacity

limit of sustainability that an environment has in relation to the size of a species population.

Overshoot

population exceeds the carrying capacityof the environment.

Dieback (population crash)

growth becomes negative, and the population decreases suddenly.

What determines carrying capacity

biotic potential AND environmental resistance

Lag phase

slow growth period because the population is small.

What Happens When the Population exceeds “K”?

Population crash

Density-independent population controls

factors that will affect the size of a population regardless of its density.

Stable population curve

population fluctuates slightly above/below “k”. (undisturbed tropical rain forest)

Irruptive population curve

normally have fairly stable population that may occasionally “explode” or “irrupt” to a high peak and then crash to a lower, more stable level. Can occur due to more predators/less food in habitat. (racoon)

Cyclic “boom-bust cycles”

rhythmic fluctuations where populations experience rapid growth followed by significant declines.

Irregular population cycle

unpredictable

6 key features of living systems

Interdependence, Diversity, Resilience, Adaptability, Unpredictability, Limits

External factors

habitat quality, food availability, and interactions with other organisms.

Internal Factors

physiological stress due to overcrowding, maturity, body size, and hormonal status.

Natality

production of new individuals

Fecundity

physical ability to reproduce

Fertility

measure of the actual number of offspring produced

Immigration

organisms introduced into new ecosystems

Mortality

Death rate

Survivorship

percentage of a cohort surviving to a certain age

Life Expectancy

probable number of years of survival for an individual of a given age

Emigration

the movement of members out of a population.

Demographic bottleneck

just a few members of a species survive a catastrophic event such as a natural disaster

What reduces genetic diversity

Founder effects and demographic bottlenecks

Minimum Viable Population (MVP)

is the minimum population size required for long-term survival of a species.

Cohort

group of individuals born at the same time

Type I survivorship curve

most individuals survive until old age

Type II- survivorship curve

decreases consistently over time

Type III survivorship curve

most individuals die early

Opportunistic pattern

Small size, mature early, short life span. Offspring are small, many

produced with little parental care

Equilibrium pattern

Size of population remains around carrying capacity.

Interspecific interactions play a central role in population dynamics by

affecting the processes of birth and death.

Interspecific interactions can function as agents of natural selection because

These interactions influence survival and reproduction.

Commensalism

+/0

Mutualism

+/+

competition

-/-

parasitism

+/-

predation

+/-

Darwin based his idea of natural selection on

competition, the “struggle for existence”.

Competition

It is regarded as a major force behind species divergence and specialization.

Interspecific competition

is a relationship that affects the populations of two or more species adversely.

Intraspecific competition

is the same relationship but occurs among individuals of the same species.

How many types of interspecific competition

6

Consumption

inhibits another by consuming a shared resource

Preemption

competition occurs when the occupation by one individual precludes establishment by others

Overgrowth

competition occurs when one organism grows over another and inhibits access to an essential resource

Chemical Interaction

It involves the production of chemical growth inhibitors or toxins released by an individual

Territorial competiton

the behavioral exclusion of others from a defended territory

Encounter competiton

results during non-territorial meetings (fighting over carcass)

Niche

the total range of environmental variables where an organism can survive, grow, and reproduce

who came up with the idea of a Niche

Bronmark and Lars-Hansson 2005

Fundamental Niche

ideal range of conditions (temperature, food, space, etc.) a species could potentially survive and reproduce in, without any limiting factors like competition or predation.

Realized Niche

often a subset of the fundamental niche, as biotic interactions can limit a species' ability to utilize the full range of its fundamental niche (always smaller)

G.E. Hutchinson proposed

A niche is a multidimensional response called a hypervolume

Competitive Exclusion Principle (Gause 1930)

organisms cannot coexist at equilibrium conditions

Geospiza fortis

large beaks

Geospiza fuliginosa

large size

Ecological Release

The process in which a species will undergo niche expansion under conditions of reduced interspecific competition (usually on islands)

Balanus balanoides vs. Cthamalus stellatus

Balanus is a superior competitor. – Chthamalus is more resistant to desiccation.

r-strategists

typically short-lived and inhabit unstable/unpredictable environments (high reproductive rates)

K-strategists

competitive species with stable populations of long-lived individuals (mortality related to density)

J.N. Chatworthy (Oxford University)

examined the growth of white clover plant(Trifolium repens) at different population densities.

– Results show an inverse relationship between growth rate (mean weight/plant) and population density.

M. Dash and A. Hota (Sambalpur University, Orissa, India)

studied the effect of population density on growth and development of tadpoles of Indian bullfrog (Rana tigrina).

Self-thinning (originally described in forest trees)

The progressive decline in density and increase in growth (biomass) of remaining individuals caused by density-dependent mortality (mostly in plant populations and sessile animals)

Self thinning rule

relationship between av. size surviving plants (increases) and pop. density remaining (decreases)

harp seals

(Phoca groenlandica)

Agonistic Behavior

Encounters are rare, Gestures, postures, vocalization that threaten an animal are understood and the threatened animal backs off or display a submissive behavior

• Limits aggression leading to fatalities

• Tends to be ritualized

Territoriality Territory

area occupied by an animal which it defends against others

Methods of territory defense

Song and call

Spreading wings and tail (birds)

Baring fangs (mammals)

Attack and chase

Marking with scents

what is the number of territorial owners that a habitat can support

equal to the total area available divided by the average territory size.

LOKTA-VOLTERRA MODEL

Prey population (x):

dx/dt = ax - bxy

•a represents the prey's intrinsic growth rate.

•b represents the rate at which predators consume prey.

•xy represents the predation term,

where the rate of prey consumption is proportional to the product of

predator and prey populations.

•Predator population (y):

dy/dt = -cy + dxy

•c represents the predator's death rate.

•d represents the rate at which predators increase by consuming prey.

•dxy represents the predation term, where the rate of predator

increase is proportional to the product of predator and prey

populations

Lotka-Volterra equations predicts

staggered oscillations.

three (3) possible outcomes to predation

1. Predator exterminates prey (brown tree snake, sea lamprey). Usually in human-altered environments.

2. Predator barely puts a dent in prey population (lions preying on wildebeest).

3. Predator controls prey population. Sometimes get a trophic cascad (Trickle-down

effect on entire community).

Predator that helps structure entire community is

a keystone predator

Sea urchins graze on

kelp

Sea otters feed on

sea urchins reducing the intensity of grazing and allow kelp to develop dense populations

otter declines due to

killer whales

why did killer whales start eating otters

declines in the whale's primary food of sea lions had forced them to start consuming otters. – Decline in sea lions was due to decline in salmon due to dams and pollution

what type of predator are more likely to create behaviorally mediated cascades

ambush

Lotka–Volterra model is widely criticized for

overemphasizing the mutual regulation of predator and prey populations.

other factors that influence predator prey interactions

Cover or refuges for the prey

Difficulty of locating prey as it becomes scarcer

Choice among multiple prey species

Coevolution

functional response between prey and predator

is the relationship between the per capita predation rate (number of prey consumed per unit time per individual predator) and prey population size

type 1 functional response

predation is constant and is independent of prey density

type 2 functional response

Many predators devote time to both searching and handling prey

Prey mortality rate declines with increasing prey density.

– Most common for vertebrate predators

– Sometimes prey sync reproduction so as to “swamp out” predators (mayflies, cicadas).

type III functional response

is low at first, increasing in a sigmoid (S-shaped) fashion as the rate of predation reaches a maximum.

– Initial rate of prey mortality increases with prey density

can control prey population

why does type 3 have a sigmoidal response

-- Availability of cover: the susceptibility of prey individuals will increase as the population grows and hiding places become filled.

– Search image: the ability of a predator to recognize a prey species will increase as the prey population size increases.

Prey switching

the act of a predator turning to a more abundant (but maybe less preferred or palatable), alternate prey.

bulk feeding

Within 48 hours of feeding, Burmese pythons can undergo up to a 44-fold increase in metabolic rate and the mass of their major organs can increase by 40 to 100 percent.

– A few sets of genes influence the change of pythons' internal organ structure.

– Key proteins, produced and regulated by these important genes, activate a cascade of tissue-specific signals that lead to regenerative organ growth.

advantages of bulk feeding

Upon feeding, the size and function of these organs, along with their ability to generate energy, dramatically increase to accommodate digestion.