BIOL 104 Vocab Pt. 2

Ecology

the scientific study of the relationships between organisms and their environment (i - study of the relationship between organisms themselves, ii - between organisms and their environment)

Individual

a single living organism; the fundamental unit of study in ecology

Population

a group of individuals of a single species, living together and interacting with each other

Community

a group of individuals of more than one species, living together and interacting with each other

Ecosystem

the complement of biotic and abiotic factors that interact in a system

Species richness

the number of species in a community

Rarefaction curve

Quantifying Diversity - more effort

Ways to apply more effort in quantifying diversity: more time, greater efficiency, more space, greater diversity of methods

Control for Effort

When comparing the diversity of different ecological communities, it is important to control for effort

Species evenness

Measures how equally abundant different species are in an ecosystem (similar number of individuals between species)

Shannon-Wiener Diversity Index

Used to take into account species richness and evenness into a single measure

p i - proportion of the i-th species in the community

S - number of species

H’ - weighs species richness by relative abundance

Rank-Abundance (Whittaker) Plots

Rank species according to absolute or relative abundance; plot rank vs. log(abundance) or log(relative abundance)

The length of the curve shows richness, rate of decline shows evenness

Community Patterns

Most communities exhibit a common pattern of a few species with high/intermediate abundance and many rare species

Scale

the extent (size) of the area we study - defining the scale that is relevant to a community is difficult, natural boundaries are a good measure

Species (Richness)-Area relationships

Power law: S = cA^Z

Take log of both sides: Log(S) = Log(C) + Z * Log(A)

The slope Z varies across different taxonomic groups, but generally is a value that is consistent with a doubling of the number of species for every 10-fold increase in island area

Species richness change

Through the processes of extinction (-1) and colonization (+1)

Low richness

greater rates of colonization relative to extinction leads to increase in richness towards equilibrium

High richness

Greater rates of extinction relative to colonization, richness will decrease towards equilibrium

Equilibrium Theory of Island Biogeography

The number of species present on an island is determined by a balance between immigration and extinction

Global species distribution

More species richness in the tropics than closer to poles

Hypotheses for Latitudinal Species Gradient

1 - Species diversify faster in the tropics

2 - Species have diversified longer in the tropics

3 - Primary productivity (the amount of energy fixed by autotrophs) is greater in the tropics

4 - Mid-domain effect (statistical null-model)

Known Species #

We’ve cataloged 2.2-2.5 million species

Methods of Estimating Total # of Species

1 - extrapolate temperate species abundance to tropical species

2 - extrapolations from detailed study of a particular group

3 - extrapolations using species characteristics

4 - extrapolating via rarefaction curves

4 Factors that regulate abundance of population

Birth, death, immigration, emigration

Population Ecology Master Equation

Delta(N) = B - D + I - E

Population Master Equation (Net gain/loss of individuals)

N_t+1 = N_t + B_t - D_t + I_t - E_t

Population Master Equation (per-capita)

N_t+1 = N_t( 1 + b_t - d_t + i_t - e_t)

Discrete geometric (exponential ) growth

N - number of individuals; abundance or density (which is abundance/area)

t - index variable, counts number of generations

gamma (or R) - per-generation factor of increase, dimensionless (has no units)

Population grows if gamma > 1, population declines if gamma < 1. Used for populations with synchronous reproduction.

Semelparity (d=1)

One reproduction event per lifetime of an individual (female). Death usually occurs very soon after reproduction because parent invests all their resources into reproduction. Often have many, poorly provisioned progeny with low chance of survival.

Iteroparity (d<1)

Multiple reproductive events per lifetime of an individual (female). Often coincident some form of paternal investment (animals) or extra provisioning (plants) that increases the survival of progeny.

Life-History Tradeoff

Synchronous Reproduction

Common in seasonally driven systems, aligning periods of resource abundance with reproduction and resource scarcity with the resilience stages

Asynchronous Reproduction

Births and deaths can happen any time, leading to a more ‘disorganized’ pattern of population growth

Demographic Stochasticity

The changes in population abundance can be variable depending on the timing of demographic events

As population grows, time between events like birth and death that change population size get smaller, so demographic stochasticity becomes less important as a population gets larger

Continuous-Time Exponential Growth

N: number (density) of individuals

t: time

r: ‘intrinsic rate of increase’ r = b - d

Population grows when r>0, population declines when r<0

Continuous: population changes continuously through time

Environmental Stochasticity

Weather; years with poor weather can cause direct mortality or generate food shortages, leading to population decline

Density Dependence

When demographic rates such as birth or death change with population density

Periods of high population abundance can lead to food shortages, which can lead to decline

Carrying Capacity

Occurs at the density where birth and death rate are equal

Logistic Growth

When the effect of density on gamma is linear

Continuous growth populations will approach their carrying capacity smoothly

Discrete growth populations can approach smoothly or overshoot above and below

Exploitative Competition

Individuals reduce the availability of resources such as food, water, light, and space

Interference Competition

Individuals physically prevent access to resource or opportunities such as territiories, mates, and nesting sites

Negative Density-Dependence

Effect of competition, declines in birth rate or increases in death rate

Abiotic Drivers

The non-living environment, including climate, chemical nutrients, habitat, etc. Characteristics impact where a species can grow and where it cannot

Biotic Drivers

The impact of heterospecifics (other species) have on a population via competition, predation, mutualism, or as their food resource can impact where a species can grow and where it cannot

Dispersal Barriers

Physical barriers can impede species from moving into areas that are otherwise suitable for them

Hutchinsonian Niche

The set of environmental conditions that permit a population to grow (environmental conditions for which gamma>1)

Metapopulation

A set of local populations (patches) coupled by the movement of individuals (ie immigration and emigration) among patches

Spatial Insurance

Having many patches can provide spatial insurance if extinction risk is uncorrelated across the landscape (but smaller patches can increase extinction risk at the same time)

Exploitative Interactions

Form the backbone of food chains/webs; characterized among pairs of species.

Adding more of the ‘resource’ species would increase the growth rate of the ‘consumer’; adding more ‘consumer would decrease growth rate of ‘resource’

Heterospecifics

individuals belonging to different species that interact with one another

Trophic Level

The number of links between a species and the base of the food web plus one

Bottom-Up Regulation

Herbivore carrying capacity is regulated by the supply of food (plants)

Top-Down Regulation

Plant carrying capacity is regulated by herbivory

Competitive Exclusion Principle

Two species competing for the same limiting resource in the same habitat cannot coexist indefinitely

Character Displacement

Differences among species characteristics are accentuated in regions where they overlap, leading to niche partitioning

Niche Partitioning

Allows for the coexistence of competing species, even when there is some overlap; there are many forms of niche partitioning

Resource Partitioning

competing species partition their use of resources such that each species’ growth is limited by a different resource

Predator Partitioning

Competing species are impacted by different predators or pathogens so that no one competitor can competitively exclude others

Temporal Partitioning

Competing species partition variation in the environment through time

Species need to have different sensitivities to the environment and be able to survive through unfavorable periods

Spatial Partitioning

competing species partition fine scale variation in the spatial environment; each species has some part of the environment where it is the best competitor

Interference Competition

Species can negatively impact each other by impeding their competitors access to a resource

Preemptive Competition

‘First-come, first serve’; occurs when a species utilizes a non-replenishing resource

Rule for Outcome of Competition

For a pair of competing species to coexist, each must have a greater negative impact on the growth rate of its own population (conspecifics) than on the growth of its competitor

If this is not true, one species will always exclude the other

Niche Complementarity

Coexisting species that partition niches make more complete use of available resources

There is a limit to the amount of niche space that a community can ultimately fill

Selection Effects

More species means a greater chance of including those that are more productive

Mutualism

Mutually-beneficial (positive) interaction between a pair of species

Differs from symbiosis, in which species interact and at least one benefits and none experience harm

Resource-Based Mutualism

Species engage in resource sharing; can be particularly prevalent when acquiring certain types of resources is difficult (ex: lichen = algae+fungi)

Primary Macronutrients

N, P, and K

Secondary Macronutrients

Ca, Mg, and S

Micronutrients

B, Cu, Fe, Mn, Mo, Zn, and Cl

Nitrogen Fixation

N₂ gas is unusable by plants, broken (or ‘fixed’) into a usable form (NH₃). Occurs through bacteria/archea living in root nodules, lightning, and industrial processes.

Root Nodules

Found in legumes, the most common nitrogen fixing plants; house bacteria and provide carbon, water, and other nutrients in exchange for nitrogen

Service Mutualism

One species provides a service (cleaning, pollination, seed dispersal) in exchange for resources (food, safety)

Mutualism/Parasitism Continuum

When costs exceed benefits, mutualism becomes parasitism

Parasitism

An exploitative interaction between a host (resource) and parasite (consumer)

Disease

A condition that impairs some structure or function of a living organism

Parasitism vs. Predation

Predators attack more than one victim in their lifetime while parasites attack only one victim in their lifetime

Virulence

The negative impact of a parasite on its host; diseases need to migrate to new hosts because of this

Transmission

Linked to virulence; the ability to infect new hosts is how parasite/disease fitness is measured

SIR Epidemic Model

Susceptible individuals in a population become Infected, transmission rate (beta) is the rate of change from S to I

Infected individuals Recover (or die) ar a constant per-capita rate v

R₀ (Basic Reproductive Number)

Derived from SIR model; the number of individuals that will become infected by the first infected individual in the population

If R₀ > 1, the infected population will grow

If R₀ < 1, the infected population will shrink

Contributions of Disease

Regulating the abundance of species (top-down) - viral shunt

Providing subsidies from one ecosystem to another

Vaccination

Vaccination makes a fraction (V) of the population no longer susceptible, so R₀ declines, meaning an epidemic becomes less likely

Fluxes

The processes that move energy and matter between different pools of an ecosystem

Primary production, respiration, nitrogen fixation, decomposition

Pools

The different states where energy and matter are stored

Biomass, atmospheric carbon (and other gases), soil nutrients

Primary Production

The foundation of all ecosystems since it is where energy (carbon) enters the living components of ecosystems

Gross Primary Production (GPP)

Measures the total rate of energy (carbon) fixed by photosynthesis

Net Primary Production

Measures the rate of energy fixed by photosynthesis that is stored as biomass, accounting for losses due to respiration

NPP = GPP - R (respiration)

Oceans and Terrestrial ecosystems each contribute ~half of global NPP

NPP of Land

Substantial variation in NPP across terrestrial environments, generally more variation in the tropics.

NPP of Oceans

Most of the ocean has very low NPP, the warmest parts of the ocean are not the most productive

Upwelling zones (where deep water returns to the surface) and coastal shelves (which have limited depth) have the greatest NPP

Liebig’s Law of the Minimum

Nutrients set the limit on how much carbon can be converted into biomass by photosynthesis

Only by increasing the amount of the nutrient that is most limiting, can a plant or crop achieve a greater yield

Nutrient Limitation

Nutrient addition (fertilization) weakens the strength of negative density dependence (resulting in an increased population density)

Residence Times

Tell us the amount of time a nutrient (or other agent) will spend within a particular ecosystem

Chronosequence of N

Over time total N increases in an ecosystem due to nitrogen fixation by organism

Chronosequence of P

Over time total P decreases through occlusion and leaching

Succession

The pattern of development of a typically terrestrial ecosystem

Primary Succession

Process of succession starting from bare rock (ex: the formation of a new volcanic island)

Secondary Succession

Succession following a disturbance in an already existing ecosystem (ex: fire, flood, drought)

Free Air CO₂ Enrichment (FACE) Experiments

Experiments model conditions with greater concentration of CO₂, use controls and replication and each consider the role of secondary treatment such as fertilization, herbivory, and ozone gas

Peat

An accumulation of partially decayed vegetation or organic matter, found in peatlands

Peatlands comprise app. 3% of Earth’s land but store 1/3 of Earth’s soil-based carbon; hold 2x as much carbon as forests