Ecology Exam 2

What are population range dynamics and what causes them?

It describes how species ranges are not fixed, they shift, contract and expand due to changing environmental factors and colonization.

• It often accompanies exponential growth

Describe what the following equations means: N_t+1 = N_t + (B + I) – (D+E)

It shows the size of the population at a future time is equal to

the current population, plus those added, minus those removed

what does a per capita value give us

It shows a change per unit of population to proportion different population sizes

Why do we use life tables?

To extract more information about a population and how/why it grows or doesn’t grow through time. It is a method to study demography

• it show age specific birth and death rates

Survivorship curves and types

shows how different classes of ages survive through time due to differences in mortality.

Type I - higher young survivorship and mortality in older ages

Type II - constant survivorship across ages; equal chance that organism dies throughout their entire life cycle

Type III - High mortality of young but have lower rates or mortality at older ages

R₀

The net reproductive rate per individual

=Sum of (l_xm_x)

for non-overlapping generations, it is the amount of female offspring produced per female during their lifetime

l_x = proportion surviving to day x

m_x = Average number females offspring produced per female

• value over 1 means population is growing

• value under 1 means population is declining

geometric rate of increase

N_t+1/N₁

_{the ration of the population size at two time points; how many times bigger the population gets at distinct times}

• same value as R₀ for non-overlapping generations

Steps for overlapping generations

• first calculate generation time

• then calculate r (per capita rate of increase)

T = (∑xl_xm_x)/ R₀

r = [ln(R₀)]/T

• if r is negative, population is declining; if positive population is growing

Population Growth

refers to the change in population size or density over time. growth can be positive or negative

population changes are determined by both the organism’s growth potential and the environment

Types of population growth

Geometric growth - often describes non-overlapping generations; no constraints, rapid growth

Exponential Growth - often describes overlapping generations; no constraints, rapid growth

Logistic growth - environmental constraints, limited growth

Characteristics of populations without limiting factors

• introduced to a new environment

• populations rebounding from a catastrophe

• low population densities and favorable environments

cannot be sustained indefinitely

Limits to population growth

• density-dependent factors - proportional effects depend on population size; proportion of population dying because some factor increases with population size

  • ex. disease, competition for resources (mostly biotic)

• Density independent factors - proportional effects do not depend on population size; probability of individual dying is not related to population

Carrying Capacity

(K) the maximum number of individuals of a population the environment can support

• at K, birth rates must equal death rates and population growth is 0

Logistic Population Growth

dN/dt = r_maxN(1-N/K)

• when population density is low, growth rate is nearly exponential

• when population density is high, growth rate gets smaller

• when population reaches carrying capacity, growth rate is 0

r vs k selection

r-selection favors rapid population growth and colonizing ability; favors presence is disturbed habitats; far below carrying capacity

k-selection favors efficient use of resources and competitive ability; favors presence in stable habitats

reproductive strategies for k and r selection

k-selected: late reproduction, few offspring, invest a lot in raising offspring

r-selected: early reproduction, many offspring, little parental care

characteristics of k and r selected species

r: high r_max , rapid development, early reproduction, small body size, many offspring, one reproduction event

k: low r_max , high competitive ability, slow development, late reproduction, large body size, repeated reproduction events, fewer offspring

phenology

the timing of life history events or ecological events

• often in relation to climate or weather

• long term records are often used

community ecology

includes interactions between just two species, interactions among all species present and everything in between

competition

negative interaction between organisms resulting from a shared requirement for a resource that is in limited supply

• reduces the fitness of both but one may have more reduced fitness than the other

• competition for water, nutrients, food, light, space

• usually between individuals but can have population level consequences

• can occur between individuals of same or different species

effects of competition

• decreased contribution to the next generation

• decreased survival or fecundity

• individuals involved obtain fewer resources, growly slower, have fewer offspring and have lower chances of survival

• effects of competition are density dependent

Types of competition (who)

intraspecific competition: competition among individuals of the same species

interspecific competition: competition among individuals of different species

mechanisms of competition

exploitative competition: competing individuals do not interact directly with each other, but instead depress abundance of a resource

interference competition: direct interaction between individuals

• both types can occur between intra and inter specific competition

Niche

all factors that influence growth, survival and reproduction of a species

fundamental niche: defined only by abiotic factors

realized niche: defined by abiotic plus biotic factors

Principle of competitive Exclusion

two species with identical niches cannot coexist indefinitely, one species will be a better competitor and exclude the other.

• species with similar niches will compete more with each other than species with very different niches

Fecundity definition

the biological capacity or potential reproductive rate of an organism to produce an offspring

types of exploitative interactions

predators-prey, herbivory, parasitism, parasitoids

parasites vs parasitoids

parasites- consume live tissue of other organisms but usually don’t kill the host

parasitoids- insects whose larvae consume their hosts and kills it, functionally equivalent to predation, not parasitism

predatory adaptions

• keen hearing

• larger eyes to see in the dark

• jaws/teeth/beaks for ripping and tearing

• camouflage and other stealth methods

Anti-predatory defenses

• morphological: spines, armor, camouflage, coloration, large size

• behavioral differences: aggressive behavior, increasing apparent size

• chemical defenses: toxins, digestion-reducing compounds, warning coloration

• safety in numbers (predator satiation - synchronous reproducing)

Parasitism

a parasite refers to an animal or protist while pathogens are viruses, bacteria or fungi

infected hosts may exhibit altered behavior which may increase the likelihood of infecting another host or being eaten

Host-parasitoid interactions

• parasitoid are insects that parasitize other insects

• adult female parasitoids lay eggs on their insect host; parasitoid larvae hatch and slowly consume the host

• parasitoids often specialize on a narrow range of host species

Predator prey interactions

predator removal studies reveal that prey populations depend on predator populations; if predator populations go down, prey populations go up

Time series analysis of predator prey cycles

• population cycles of predator-prey species occur about every 10 years in hares and lynx

• similar cycles occur in other small mammal populations

• food and predator numbers are main factors on prey populations

• predator dynamics lags slightly behind prey dynamics

functional response (curves)

relationship between availability vs. consumption rate

type 1: linear increase then levels off; food intake proportional to prey abundance then levels off

type 2: slope of line continually decreasing then levels off;

type 3: s-shaped curve

Mutralism

individuals of both species benefit from the association but still involve some costs; interactions between individuals of different species which results in increased fitness of both partners

• benefits must outweigh costs for association to continue

Types of mutralism

facultative mutualism- species benefit from a mutualistic partner but can survive and reproduce without them

obligate mutualism- species cannot survive or reproduce without partner

important examples of mutualism

• mycorrhizae and nutrient uptake by plants

• plants and bacteria

• coral reefs and zooxanthellae

• pollination

• seed dispersal by animals

• ants and plants