ecology exam 1

ecology

the scientific study of the biotic and abiotic factors that determine the distribution and abundance of organisms

individual organism

the organismal level of study, which focuses on the behavior, physiological, and morphological adaptations an individual uses to deal with its environment

population

a group of individuals of a single species at a particular place and time and have the potential to interbreed and interact

community

a group of species at a particular time and place and the interactions that bind them

ecosystem

a set of interacting species plus the physical space they occupy

landscape

a large area composed of a interacting ecosystems

biosphere

the whole earth ecosystem

biological evolution

a genetic change in a population over generations or a change in gene frequency through time

cause

• mutation

• natural selection

• genetic drift

• migration (immigration and emigration)

genetic change

a change in the genetic makeup of a population over time

adaptive evolution

a genetic change in a population over time that leads to higher fitness

fitness

a success of a phenotype relative to other phenotypes; in terms of reproduction or survival

natural selection

differential survivorship or reproduction phenotypes

requirements

• phenotypic variation

• differential survival/reproduction

genetic drift

random fluctuations in allele frequencies across generations

phenotypic variation

differences in physical physiological or behavioral traits among individuals within a population

differential survivorship/reproduction

the unequal survival and reproductive success of different phenotypes in population which directly determines relative fitness differences

phenotypic plasticity

the ability of a single genotype to produce different phenotypes under different environmental conditions

directional selection

a mode of natural selection that acts against phenotypes at one extreme of the distribution, shifting the population’s average trait value toward the opposite extreme over time

stabilizing selection

A mode of natural selection that acts against extreme phenotypes on both ends of the distribution, favoring the intermediate (average) phenotype and reducing trait variance without shifting the mean

diversifying selection

A mode of natural selection that acts against the average (intermediate) phenotype, favoring individuals at both phenotypic extremes

evolutionary constraints

facts that prevent evolution of optimal design

• changing environment

• laws of physics

• genetic limitations

• genetic drift

founder effects

an evolutionary phenomenon (associated with genetic drift) that occurs when a new population is established by a very small number of colonizing individuals ("founders")

migration

change in gene frequency within a population due to the influx (immigration) and/or outflux (emigration) of individuals

coevolution

reciprocal evolutionary change occurring in two interacting populations or species

deme

(subpopulation) spatially or physically isolated subdivisions of a larger population where members are highly likely to interact and interbreed with one another

metapopulation

a collection of subdivided populations linked together by migration and dispersal

unitary forms

organisms that exist as highly predictable, single individuals with distinct physiological boundaries

modular forms

organisms that grow by the repeated addition of genetically identical modules (clones) often sharing interconnected root systems

density

number of individuals of a single species per unit area or volume (N)

spatial structure

The spatial distribution pattern of individuals within a population's geographic range

age structure

proportion of individuals in each age class within a population

population ecology

the study of population characteristics (size, density, spatial structure, age structure), their inter-relationships, and how they change in time and space

emigration rate (e)

The per-capita rate measuring the number of outgoing individuals leaving a population per individual in the population over a given unit of time (E_t/ N_t). In population models, it is used to calculate the overall decrease in density due to emigration (N_te)

immigration rate (i)

The per-capita rate measuring the number of incoming individuals entering a population per individual already in the population over a given unit of time (l_t / N_t). In population models, it is used to calculate the overall increase in density due to immigration (N_ti)

mortality

The loss of individuals from a population due to death (D)

birth rate (b)

The per-capita rate of reproduction in a population, calculated as the total number of births (B_t) divided by the population size (N_t) at a given time (b_t = B_t/ N_t)

death rate (d)

The per-capita rate of mortality in a population

cohort

an even-aged group of individuals followed from birth to death

demography

the study of the effect of age structure and other population parameters—such as births (B), deaths (D), immigration (I), and emigration (E)—on population growth (r)

age-specific survivorship (l_x)

The proportion of individuals surviving from birth (x=0) to the start of age class x, calculated as l_x= n_x / n₀

age-specific fecundity (b_x)

The average number of female offspring produced per female during the age interval x

vital rates

The combination of survival schedule (l_x) and reproductive schedule (b_x) that determines population dynamics

survivorship curves

Graphs plotting the number of survivors (n_x) or proportion surviving (l_x) on a log scale against age (x).

They fall into three classic archetypes

• Type I: Low mortality in early life, with high mortality concentrated among older individuals.

• Type II: Approximately constant rate of mortality throughout the entire lifespan.

• Type III: Extremely high mortality among juveniles, followed by high survival rates for the remaining life stages

potential fecundity

The total number of female offspring a female would produce if she survived to the end of the final age class

net replacement rate (R₀),

The expected number of female offspring produced per female per generation, calculated as R₀ = ∑ l_x b_x

generation time (T)

The mean period of time elapsing between the birth of parents and the birth of all their offspring, calculated as T = ∑ xl_x b_x/R₀

geometric growth

a population growth model characterized by non-overlapping generations, where population size increases by a constant ratio at discrete intervals

stable population

a population with constant age-specific birth and death rates over time, resulting in a constant age structure and a stable per-capita rate of population growth.

exponential growth

A model of unrestricted population growth in continuous time, represented by the differential equation dN/dt = rN or the integrated form N_t = N₀e^rt It assumes overlapping generations, constant vital rates, and no limiting resources

overlapping generations

a population structure where multiple generations co-exist in time and breed simultaneously

non-overlapping generations

a population structure where older generations die off before subsequent generations mature and reproduce.

intrinsic rate of increase (r)

The maximum per-capita rate of population growth in a closed system, calculated as r = b - d

• If r > 0, the population increases exponentially

• if r = 0, the population size is stable

• if r < 0, it declines exponentially

realized per capita growth rate (dN/Ndt; realized growth rate per individual)

The actual growth rate per individual at any given moment in time.

• Under exponential growth, it remains maximal and constant (dN/Ndt = r).

• Under logistic growth, it is density-dependent and decreases linearly as density (N) increases (dN/Ndt = r[(K-N)/K])

limiting resource

an essential resource (such as food, space, light, water, minerals, or pollinators) that is in short supply and limits population growth

competition

an interaction that occurs when organisms share a limiting resource, reducing the fitness, survival, or growth of the competitors

exploitative (scramble) competition

indirect competition where whoever accesses the limiting resource first consumes it, leaving less for others

interference competition

direct competition where organisms actively harm or physically block each other from accessing resources

intraspecific competition

competition between members of the same species

interspecific competition

competition between members of different species

carrying capacity (k)

the maximum population size at which a limiting resource is fully utilized (where resource consumption equals availability), serving as a stable equilibrium point where population growth is zero

equilibrium

a state of a population where the growth rate is zero (dN/dt = 0) and population size remains constant over time

stable equilibrium

an equilibrium point (like carrying capacity K) to which a population converges; if the population is disturbed above or below this point, it naturally returns to it

logistic population growth

A sigmoidal growth model where the rate of population increase declines linearly as density (N) approaches carrying capacity (K), represented as dN/dt = rN [(K-N)/K]

intraspecific competition function (ICF)

The term [(K-N)/K] in the logistic growth model, which measures the proportion of resources remaining unused or the proportion of population growth capacity remaining

density dependent growth

a pattern of population growth where vital rates and the realized per-capita growth rate are directly influenced by population density (predicted by the logistic model)

density independent growth

a pattern of population growth where vital rates and the realized per-capita growth rate remain constant regardless of population density (predicted by the exponential model)

life history

an organism’s lifetime pattern of growth, maturation, reproduction, and death, consisting of demographic parameters (l_x, b_x, R₀, r, K)

life-history trait

Any phenotypic trait (such as lifespan, age of maturity, body size, or clutch size) that directly affects demographic parameters

life history strategy

the suite of co-adapted life history traits possessed by an organism that determines its overall pattern of growth, reproduction, and survival in its environment

r-k selection

a general life-history theory developed by MacArthur & Wilson (1967) using predictions from the logistic model to explain trait suites

r-selection

favored in low-density, unpredictable, or frequently disturbed environments; selection favors traits that maximize reproductive output and rate of population increase (r), such as early maturity, short lifespan, small size, and many small offspring

k-selection

favored in high-density, crowded, stable environments; selection favors traits that maximize competitive ability and resource efficiency near carrying capacity (K), such as late maturity, long lifespan, large size, few large offspring, and extensive parental care

ecological equivalents

species with highly similar life-history traits and ecological niches that occur in geographically separated but structurally similar environments

opportunistic/weedy species

organisms characterized by r-selected life-history traits that exist well below carrying capacity and colonize disturbed environments

equilibrium species

organisms characterized by K-selected life-history traits that stably maintain population sizes at or near carrying capacity in stable environments

r-k dichotomy

the classic categorization of species strictly into either r-selected or K-selected traits, which only fits about 50% of real-world species

r-k continuum

he realistic spectrum of life-history strategies, ranging continuously from extreme r-selection to extreme K-selection, along which real species are distributed

the evolution of horses

concept: adaptive evolution

the study: over 55 million years, researchers mapped a simplified family tree of the genus Equus and tracing its lineage back to its ancient dog-sized ancestors hyracotherium

found: this is an example of body size increasing over generations that led to higher relative survival and reproductive success (higher fitness) in their changing environments

**natural selection does not produce a perfect organism, only a better fit one (laws of physics)**

directional selection in the peppered moth

concept: directional selection

the study: light colored morph and dark colored morph of the peppered moth

found: prior to the industrial revolution, the dark morph was extremely rare but after the industrial revolution, the head coal soot covered trees, killing light colored moths which resulted in a directional selection and dark colored moths became common.

study of the evolution of spot number in guppies

concept: directional and stabilizng selection

the study: how spot number shifted under different selective pressures

found:

• in predator free streams: female guppies preferred mating with males that have more spots, so sexual selection acts as directional, pushing the average male spot count higher.

• in predator dense streams: these bright spotted guppies are easily hunted, so natural selection via predations acts as a directional selection against spotted males

• in streams where mating and predation is present, natural selection acts against both extremes, so guppies have an intermediate number of spots representing stabilizing selection

study of puberty and body size in English men and women

concept: directional and stabilizing

the study: natural selection acting on age at puberty and adult body height

found:

• age of puberty: exhibits directional selection in human females, natural selection favors later or older age in puberty, shifting the population mean over time

• body size: exhibits stabilizing selection because it acts against extreme height phenotypes in both males and females, maximizing relative fitness at intermediate heights

study of clutch size in birds (see wood duck example)

concept: stabilizing selection

the study: clutch size

found: natural selection acts against extreme clutch sizes. if a parent lays too little eggs, their overall reproductive output is too low. if they lay too many eggs, they cannot successfully feed or protect the massive brood, maximizing in offspring mortality. so, parental fitness is maximized at an intermediate, optimal clutch size

study of African Swallowtails

concept: diversifying selection

the study: wing color

found: 2 extremes mimic either a toxic or unpalatable species and intermediate that doesn’t mimic any species. natural selection favors both phenotypic extremes and selects against the intermediate individuals

study of genetic drift in fruit flies

concept: genetic drift

found: By generation 1, the allele frequencies in individual populations already began to randomly deviate from 0.511. Over successive generations, random sampling error caused allele frequencies to wildly fluctuate. By generation 19, the vast majority of the 107 jars had either completely fixed the brown eye allele (frequency = 1.0) or completely lost it (frequency = 0.0). This provided direct experimental proof that genetic drift occurs rapidly and can drive alleles to fixation or loss when population size (N) is small

study of founder effects in island populations

concept: founder effect and genetic drift

found: island populations often begin with only a few founders and stay relatively small. Because the founding individuals carry only a portion of the original population’s genetic variation, some alleles may be missing from the new population from the very beginning. Small population size then makes genetic drift even stronger, increasing the chance that alleles are lost or become fixed. This is why island populations often have less genetic variation than mainland populations

study of founder effects in silvereyes

concept: founder effect

found: With each successive colonization event moving further from the mainland, the new island population’s allelic diversity dropped in a clean, stepwise fashion. Because each island was colonized by a tiny subset of individuals from the previous island, each step created a genetic bottleneck, illustrating a literal geographic chain of founder effects.

study of migration and genetic change in the Glanville fritillary

concept: metapopulation migration and gene flow

found: The Glanville fritillary exists in separate subpopulations that are connected by dispersal, forming a metapopulation. Haag et al. studied flight metabolic rate (FMR), which is related to dispersal ability and has a genetic basis linked to the pgilocus. They found that isolated populations were more likely to be founded by butterflies carrying the pgi-f allele, which is associated with greater dispersal ability. This means migration was non-random because butterflies with certain genetic traits were more likely to disperse and establish new populations. As a result, migration can change allele frequencies and influence the genetic structure of populations within a metapopulation.

study of coevolution in gastropods/bivalves and their predators

concept: predator-prey coevolutionary arms race

found: Over millions of years, the percentage of gastropod families possessing thickened shells steadily rose as an adaptation to reduce crushing predation. In response to these thicker defenses, crab and lobster lineages evolved significantly larger claws and greater claw crushing strength. This reciprocal evolutionary back-and-forth between interacting species serves as the classic demonstration of a coevolutionary arms race

study of the dispersion of stingless bees

concept: behavioral drivers of spatial structure

found:

• The four highly aggressive species exhibited a clean, uniform (regular) distribution. This is driven by aggressive behavior: rival colonies of these species battle daily (sometimes for weeks) for physical possession of potential nest trees, forcing colonies to remain evenly spaced out.

• The fifth, non-aggressive species (T. dorsalis) exhibited a random distribution because colonies do not interact antagonistically, leaving nest placement independent of other colonies

life table analysis of Darwin’s finches

concept: type 2 survivorship in birds

found: By constructing a complete life table from birth to death, the Grants plotted a survivorship curve showing that Darwin's ground finches follow a Type II survivorship curve. The finches died at a constant rate of approximately 25% mortality per year regardless of their age, representing a linear decline when plotted on a logarithmic scale

Loggerhead turtle life table analysis

concept: stage based demography applied to conservation

found: The model proved that sea turtle population growth is highly sensitive to the survival of juveniles and subadults, rather than eggs. Historically, conservation efforts focused entirely on protecting beach nests and eggs. Crouse's study directly resulted in federal laws mandating Turtle Excluder Devices (TEDs) in shrimp trawls (which NOAA found are 97% effective at letting turtles escape), triggering a historic population recovery

theory of r and k selection

concept: evolutionary life history strategies

found:

• r-Selection: Expected in unpredictable, low-density, or frequently disturbed environments where resources are temporarily abundant. Selection favors individuals that maximize the per-capita rate of population growth (r). Traits include: short lifespan, early maturation, small body size, producing many small offspring, and rare parental care (e.g., opportunistic/weedy species)

• K-Selection: Expected in stable, crowded, high-density environments near carrying capacity (K) where competition is intense29. Selection favors traits that maximize competitive ability and resource utilization efficiency. Traits include: long lifespan, late maturation, large body size, producing few large offspring, and common parental care (e.g., equilibrium species)

• The Continuum: While some species fit this dichotomy, many (like the long-lived, small-clutched Wilson's storm petrel) fall along an r-K continuum, showing that life history is a spectrum

uniform

evenly spaced individuals; driven by competitive interactions between individuals such as territory

random

spacing independent of other individuals; driven by neutral interactions between individuals and the environment

clumped

aggregation in groups; driven by cooperative social behavior, group benefits, or patchy resource distribution