Bio 2 Test #2

Population

A group of individuals of the same species living in the same geographic area at the same time

metapopulations

populations of the same species linked together through dispersal 

Population size at time (t)

= N (t-1) + birth + immigration – death – emigration

Closed population

no exchange of individuals with other populations, i.e. assume no immigration/emigration

transect

sampling method - a path along which one counts and records occurrences of the species of study

quadrat

sampling method - a small plot to isolate a standard unit of area for study of the distribution of immobile or slow-moving organisms over a large area. 

Crude density

number of individuals per unit space 

Ecological density

number of individuals per unit area of habitable habitat

Peterson-Lincoln estimator of population size

N = total pop. estimate

M = Number of individuals captured in first sample and marked

n = number of individuals recaptured in second sample

m = number of marked individuals in second sample

m/n = M/N

N = nM/m

Errors of Peterson-Lincoln estimator of population size

• Learn to avoid capture in the second round

• same animals may preferentially be re-trapped—especially if a food reward is offered

• may be harmed by the marking technique, reducing their survival

• The approach also assumes that animals don’t die, get born, leave, or enter the population during the period of the study

cohort

a group of same-aged individuals that grow and survive at similar rates

Life Table equations

Age class: x

number alive: nx

number dying: dx = (nx + (nx+1))

Pop. surviving: lx = nx/n0

mortality rate: qx = dx/nx

Avg # alive in age class: Lx = (nx + (nx+1))/2

Total years lived: Tx = summation Lx

Life expectancy: ex = Tx/nx

fecundity: mx (average # of offspring produced at that age)

reproductive rate: R0 = summation (lx)(mx) + …

Survivorship Curve

Graph

Population growth rate

r = lnR0/g

g = generation time

Recall R₀ =1, the population is stable

• Given ln (1) = 0 

r = 0 (stable population) 

r> 0 population is growing 

r<  0 population is shrinking

unit for r = year -1

Population growth curve - exponential

dN/dt = rN

• resources not limited

• instantaneous population growth (dN/dt) increases as the population increases (density independent growth)

• r remains constant throughout the process

• j shape

Factors that limit population growth

• Density independent factors

  • Often abiotic in nature 

• Density dependent factors 

  • Often biotic in nature 

Carrying capacity (k)

max. pop. size of a biological species that can be sustained by that specific envioronment

Population growth curves - logistic

• resources limited (carrying capacity)

• instantaneous population growth (dN/dt) decreases as the population increases (density independent growth)

• S shape

dN/dt = rN(1 - N/k)

Life History

lifetime pattern of growth, development and reproduction

Fitness

number of viable offspring that is produced

Three key components of life history

• Survival

• Reproduction

• Maturity

Semelparity

Reproduce only once before dying, e.g. squid and cicadas.

Iteroparity

Reproductive effort spread over more than one episode over its lifetime, e.g. elephants and humans

Community

a group of different species living close enough together for potential interaction

Species interactions

• competition

• Consumption

• Commensalism

• Mutualism

Competition

Individuals use the same resources (overlapping niches) – resulting in lower fitness 

Species 1 -

Species 2 -

Consumption

One organism eats or absorbs nutrients from another. The consumer’s fitness increases but the victim's decreases

Species 1 +

Species 2 -

Commonsalism

One species benefits but another species is unaffected

Species 1 +

Species 2 0

Mutualism

Fitness benefits conferred to both species involved

Species 1 +

Species 2 +

Niche concept

The range of resources that a species can use and the range of conditions that it can tolerate. More broadly, the role that a species plays in its ecosystem

Realized niche

• The portion of the fundamental niche that a species occupies given limiting factors, such as 

  • Constraints with other abiotic or biotic variable 

  • Competition with other species 

Types of competitions

• Intra-specific : within a species

• Inter-specific : between species

Mechanism of competition

• Consumptive or exploitation competition: Compete through resource depression or depletion

• Interference competition: Compete through direct interactions (chemical or behavorial)

Types of consumptive interactions

• Predation

• herbivory

• Parasitism

Predation

A predator kills and consumes all or most of its prey

Herbivory

plant eater

Parasitism

organism that lives in or on a host taking resources from it

Endoparasite

consumes a relatively small amount of tissue or nutrients from inside the host

Ectoparasite

consumes a relatively small amount of tissue or nutrients from outside the host

Parasitoid

free living as an adult but endo or ecto when larva (young)

Constitutive defense

traits that are present even in the absence of predator

Mimicry

Phenomenon characterized by the superficial resemblance of two or more organisms that are not closely related taxonomically

Inducible defense

• Physical, chemical, or behavioral defensive traits that are induced in the prey in response to the presence of a consumer. 

  • Plants are famous for inducible chemical toxics e.g., cyanide, nicotine, caffeine, morphine.

Co-evolution

A repeating cycle of reciprocal adaptation often happens when predator and prey, herbivores and plants, or parasites and hosts interact over time.

Functional response of predator

• Type I : Linear increase in consumption rate until satiation, then no change in consumption rate above satiation. 

• Type II: Consumption rate increases at a decelerating rate, gradually leveling off at maximum rate. 

  • Common 

• Type III: Sigmoid increase in consumption rate as prey density increases. 

Mechanisms behind type III functional responses

• Prey switching 

• Learning 

• Limitation of prey refuge

Trophic cascade

• Predators can shape their community through indirect interactions. 

• Presence of predators can affect herbivores, which in turn indirectly affects primary producers. 

  • The indirect interactions can either be density-mediated (i.e. primary consumer got eaten) or trait-mediated (i.e. primary consumer goes into hiding). 

“Keystone species”

• A species which has a disproportionately large effect on its natural environment relative to its abundance. 

  • Lay science description is MISLEADING 

Keystone is CONTEXT-dependent.

The 10% rule

• Energy transfer between trophic levels is inefficient. Only about 10% of the net productivity of one level ends up as net productivity at the next level.

• Why? 

  • Partial consumption: not all the organisms at a lower trophic level get eaten by those at a higher trophic level. 

  • Incomplete digestion and assimilation: Some parts of the lower trophic level do get eaten but are not digestible by predators and are lost in the predators' feces. 

  • The dead bodies and feces are remineralized by decomposers. 

  • Energy is loss in the process of cellular respiration, as heat 

Homeostasis

The array of relatively stable chemical and physical conditions in an organism’s cells, tissues, and organs.

conformational homeostasis

achieved by passively matching the conditions of a stable external environment

regulatory homeostasis

active physiological processes triggered by variations in external of internal environment

Why keep conditions within a tolerate range?

• Homeostasis

• Structure and function of enzymes is influenced by temperature, pH, and other physical and chemical conditions 

  • Extreme high temperatures can denature proteins 

• Temperature affects membrane permeability

  • Thermal expansion of water  at extreme cold can rip cells and damage tissues 

• Temperature affects diffusivity (how fast solute diffuse in a medium) 

Negative feedback

• restoring feedback

• feedback serves to reduce an excessive response and keep a variable within the normal range.

Positive feedback

• reinforcing feedback

• feedback serves to intensify a response

Heat exchange with the environment

• Radiation 

• Convection 

• Conduction 

• Evaporation

Bergmann’s rule

• Within a broadly distributed taxonomic clade, populations and species of larger size are found in colder environments, while populations and species of smaller size are found in warmer regions

• Rationale is that larger body size reduce radiative heat loss

Allen’s rule

• Animals adapted to cold climates have shorter limbs and bodily appendages than animals adapted to warm climates

• Once again to reduce surface area to volume ratio to limit heat loss.

Thermoregulation in ectotherms 

• Behavioral means are often used to regulate body temperature 

  • Exploiting microclimates

  • Seeking shade to cool down 

  • Locating sunny place to warm up

  • Raising the body from the ground to decrease conductance 

  • Underground burrows 

Temperature and performance in endotherm

Thermal neutral zone refers to the range of temperature which endotherm does not need to alter metabolic rate to maintain constant body temperature (T_b)

Countercurrent heat exchange

• Given water has a high specific heat capacity, it is a good conductor 

• Aquatic animals often have special adaptation to reduce heat loss

Heterothermy 

• Hummingbirds reduce their activities at night, bats during the day, such that endothermic organisms become poikilothermic. 

• Mammal hibernation is an example of homeothermic animals that undergo controlled hypothermia

Electrolyte

Solutes that dissociates into ions in water (NaCl 🡪 Na⁺ + Cl^-)

Osmolarity

osmotic concentration

Osmoregulation is important for

• Maintaining Protein conformation and function is affected by the presents of ions 

• Maintaining cell volume 

• Maintaining electron gradient inside and outside a cell

Difusion

solute molecules move from high to low concentration

Osmosis

Solvent molecules move from low concentration to high concentration

the net diffusion of water molecules that is caused by a difference in osmolarity between the two compartments

Net diffusion

when the flow of solute particle moving in one direction is bigger than the flow of solute particles moving in the opposite direction

Osmotic potential

• Water moves from a region where its potential energy is greater to a region where its potential energy is lower

  • Regardless of the reason for the water potential energy difference

  • Water will move until the same water potential energy is reached in all regions.

• The differences in potential energy of water between two regions can be caused by several factors 

  • Differences in entropy, osmolarity, pressure, temperature, etc.....

Osmoconformers

remain isosmotic with their surroundings and do not regulate their osmolarity

Osmoregulators

expend energy to control water uptake and loss in a hyperosmotic or hyposmotic environment

Fick’s Law of Diffusion

Q = D A ((P1-P2)/L)

• D is the diffusion coefficient (dependent on the diffusing substance, the medium, the temperature)

• A: area across which the gas is diffusing 

• L is the distance between the two locations 

• (P1-P2)/L  partial pressure gradient 

  • Partial pressure is the pressure of that constituent gas if it alone occupied the entire volume of the original mixture at the same temperature.

 

Obtaining oxygen for aerobic respiration through diffusion

Pro:
Does not require additional energy 

Con:
There is a size limit (as L ￪, Q ￬)

Henry’s Law

Cg = k * Pa

• C_g is the concentration of dissolved gas (mol l^-1)

• K is the solubility constant (temperature, salinity, and gas dependent) 

• P_a is the partial pressure of the gas in the overhead space

Ideal gas law

PV = nRT

• P is the pressure (atm)

• V is the volume of the gas (L)

• n is the number of gas particle (mol) 

• R is the ideal gas constant  (0.0821 atm•L/mol•K)

• T is temperature in Kelvin (K)