Ecology Unit 2 Updated

How is population density defined?

The number of individuals per unit area.

What are the recorded population densities for diatoms and soil arthropods?

Diatoms have a density of $5,000,000\,\text{m}^{-3}$, and soil arthropods have a density of $500,000\,\text{m}^{-2}$.

What are the population densities given for field mice and trees?

Field mice have a density of $200\,\text{ha}^{-1}$, and trees have a density of $100\,\text{ha}^{-1}$.

What are the human population densities listed for India, the USA, and Canada?

India has $371\,\text{km}^{-2}$, the USA has $34\,\text{km}^{-2}$, and Canada has $2\,\text{km}^{-2}$.

What general relationship between body mass and population density in herbivorous mammals is depicted in this graph?

There is a negative relationship; as log(body mass) increases, log(density per $\text{km}^2$) decreases.

Which songbird species is referenced when examining individuals per census route across its geographic range?

Spiza americana.

According to this model, how does dispersal influence the boundary of a population's distribution across environmental conditions?

Individuals disperse from areas of population increase (positive growth rate) to areas of population decrease (negative growth rate), which extends the limit of population distribution into poorer environmental conditions compared to the limit in the absence of dispersal.

Identify the three spatial population models shown in this diagram.

(a) Metapopulation model, (b) Source-sink model, and (c) Landscape model.

What types of patches are distinguished in the source-sink population model?

Source patches (high-quality) and sink patches (low-quality).

In the landscape model of populations, what governs the movement of individuals between patches?

Movement depends on the surrounding landscape matrix and habitats.

How is population size estimated for sessile organisms?

By counting the number of individuals per unit area and multiplying that value by the total area.

In the mark-recapture method, what ratio of marked individuals is expected in a subsequent sample assuming complete mixing?

A ratio equal to $M$ to $N$ (the ratio of marked individuals released to the total population size).

What is the formula to calculate the estimated population size ($N$) using the mark-recapture method with second sample size $n$, marked individuals released $M$, and recaptured marked individuals $x$?

$$N = \frac{n \times M}{x}$$

What insect species in Illinois varied temporally and spatially in density from a few to $1,000\,\text{per m}^2$ between the 1840s and 1930s?

The chinch bug.

What is the difference between dispersion and dispersal in ecology?

Dispersion is the spatial distribution of organisms within an area, whereas dispersal refers to the movement of individuals.

What are the three main types of spatial dispersion patterns observed in ecological populations?

Clumped, random, and even (also referred to as regular or spaced).

What defines clumped dispersion, and what typically causes it in nature?

Clumped dispersion consists of aggregated spatial patterns. It often reflects irregularities in the environment, causing organisms to concentrate in favorable spots to enhance fitness.

How is random dispersion defined in ecology?

Random dispersion is a pattern where an individual has an equal chance of occupying any point within an area, and the presence of one individual is not influenced by the position of others.

What defines even (regular) dispersion, and what is its primary ecological driver?

Even dispersion is a pattern where the spacing between organisms is approximately equal. It is typically driven by competition.

What dispersion pattern is shown among these nesting birds, and what behavioral interaction causes it?

Even (regular) dispersion, caused by competition as birds defend small nesting sites.

What chemical interaction contributes to the even dispersion pattern seen in creosote bushes?

Allelopathy.

What type of dispersion pattern is shown in this desert habitat, and what resource competition drives it?

Evenly-spaced dispersion, driven by competition for water.

What dispersion pattern is exhibited by the stands of trees shown here, and what reproductive mechanism produces it?

Clumped dispersion, produced by vegetative reproduction.

How do the seed dispersal mechanisms of Baccaurea racemosa, Shorea leprosula, and Croton argyratus affect their spatial dispersion patterns?

Baccaurea racemosa (animal dispersed) has a widespread distribution; Shorea leprosula (gyration dispersed) has moderate clustering; Croton argyratus (ballistically dispersed) shows tight clumped dispersion due to short-distance dispersal.

In a quadrat frequency distribution, why does a clumped population exhibit high frequencies at zero as well as at higher counts?

Because organisms aggregate into specific patches, leaving many sampling quadrats completely empty ($0$ individuals) while quadrats overlapping clumps contain high counts of individuals.

Which dispersion pattern generates a sharp, narrow peak centered closely on the mean value across sampling quadrats?

Even (regular) dispersion, because organisms are uniformly spaced and nearly every quadrat captures the same number of individuals.

What major ecological principle governing the measurement and detection of dispersion patterns is illustrated by varying quadrat sizes?

Dispersion depends on scale.

As one zooms in to finer scales, what environmental factors progressively determine the distribution of Clematis fremonti?

Climate, topography, soil chemistry, and soil texture.

How is the fundamental niche of a species defined?

The range of physical conditions and resources over which a species can persist.

What is the realized niche of a species, and how does it relate to the fundamental niche?

It is smaller than the fundamental niche and represents the range of physical conditions and resources over which a species can persist in the presence of interspecific interactions, such as predators, pathogens, competitors, and mutualists.

In southern Florida, what invasive bee was documented pollinating the invasive orchid Cyrtopodium polyphyllum?

Centris nitida, an invasive oil-collecting bee.

What is a geographic range, and what factors determine it?

It is the actual spatial distribution of a population, determined by physical conditions and resources (fundamental niche), biotic interactions (realized niche), and dispersal.

How is dispersal defined in the context of species distributions?

The movement of individuals from one area to another.

What climatic extremes define the geographic distribution limits for the sugar maple in North America?

Cold winters ($<-18^\circ\text{C}$), hot summers ($>24^\circ\text{C}$), and summer drought.

What distinct soil characteristics differentiate the habitats of black maple, red maple, and silver maple?

Black maple prefers drier soils high in calcium; red maple thrives in moist, well-drained soils; and silver maple grows in wet, swampy soils or dry, poor soils.

How did the geographic range of the European Starling change in North America following its introduction?

Starting in the northeastern United States in $1918$, it spread westward and southward through $1926$ and $1949$, eventually occupying virtually the entire contiguous United States and southern Canada in the present day.

Based on this range expansion map, in what country and year did the spread of Africanized Honey Bees begin in the Americas?

Brazil in $1957$.

What invasive predator is shown here, and what was its impact on the native birds of Guam between 1963 and 1986?

The Brown Tree Snake, which expanded across the entire island of Guam and decimated the native Guam bird populations until they virtually vanished.

According to the diagram, what are the four sequential steps of ecological niche modeling?

1. Map the locations where the species has been recorded (known occurrences in native distribution). 2. Graph the physical conditions found in these locations to create an ecological envelope. 3. Map the locations where those conditions occur to predict the species' distribution in its native region. 4. Map the locations where those conditions occur in an introduced region to predict potential distribution.

What climate variables are captured in the 19 bioclim layers from WorldClim used in ecological niche modeling?

Mean temperature, hottest temperature, seasonality, and precipitation.

What are three primary applications of ecological niche modeling?

Predicting invasive ranges, projecting distributions under climate change, and locating rare species.

In the study by Lozier, Aniello, and Hickerson (2009), what did ecological niche modeling using Sasquatch sightings and footprints reveal?

The model produced a bioclimatic distribution nearly identical to that of the black bear, illustrating that without rigorous data validation, niche models can produce misleading predictions.

Which two invasive plant species had their potential distributions in North America predicted using ecological niche models based on their native Asian ranges?

Hydrilla verticillata and Lespedeza cuneata.

What is the ecological definition of a population?

All individuals of a species that live in a particular area and have the capability of interbreeding.

What are two key points regarding the genetic and organizational nature of a population?

A population has a gene pool and is often 'messy', meaning it can frequently be subdivided into subpopulations.

What major categories of questions are addressed at the population level in ecology?

Population distribution and range size; population size and density; and changes over time (for example, with human influence).

What does spatial structure refer to in the context of population structure?

The distributions, density, and spacing of individuals within their geographic range.

How is age structure defined in population ecology?

The proportion of individuals of each sex in each age class.

What four factors progressively determine the distribution of plants at finer geographical scales?

Climate, topography, soil chemistry, and soil texture.

What plant species, shown here, is used as an example to illustrate how environmental factors determine distribution across finer geographic scales?

Clematis fremonti

What does it mean for a species to be endemic?

It only occurs in a particular region and nowhere else.

According to the lecture, to what specific area is Clematis fremonti endemic?

Jefferson County, MO.

How is a native species defined?

A species that normally (historically) occurs in the region.

What is an introduced species?

A 'non-native' species occurring outside of its native range.

What defines an invasive species?

An introduced species that is spreading rapidly and negatively affecting the local ecosystem.

Why do females typically perform mate choice while males compete to mate with multiple females in sexual selection?

Males are limited by mating opportunities and benefit by mating with many females, whereas females are limited by resources and benefit by mating with high-quality males that provide resources, parental care, or good genes.

What is sexual dimorphism?

Phenotypic differences between the sexes of a species.

What are the three ways sexual dimorphism can arise?

1) Differences resulting from reproductive function, 2) male-male competition, and 3) mate choice.

How do reproductive function differences drive sexual dimorphism in species such as the golden orb-weaver spider?

Females are larger than males because they produce eggs (the larger gamete) or carry offspring. Larger individuals produce more and larger gametes, creating a selective tendency toward increased female size.

How does male-male competition lead to sexual dimorphism?

Direct contests between males favor the evolution of larger body size or specialized weaponry such as antlers or horns to win access to mates.

In the Long-tailed Widowbird sexual selection experiment, how did manipulating tail length affect male reproductive success?

Males with artificially elongated tails attained the highest reproductive success (averaging nearly $2$ nests per male), control males averaged slightly below $1$ nest, and shortened-tail males had the lowest success (under $0.5$ nests per male).

What is population genetics?

The study of changes in the frequency of genes in a population across space and time.

What is a gene pool?

All of the alleles (of one or many genes) of every individual in a population.

What is the difference between a fixed gene and a polymorphic gene in a population?

A gene is fixed when all individuals carry the exact same allele, whereas it is polymorphic when there is more than one allele version in the gene pool.

In the 1960s protein electrophoresis studies on Drosophila metabolic enzymes, what proportion of genes were found to be polymorphic?

$30\%$ of metabolic enzyme genes were found to be polymorphic.

What are the primary sources of genetic variation within a species compared to within a population?

Within a species, genetic variation arises from mutation and hybridization; within a population, it comes from mutation, hybridization, and migration.

What is a mutation, and how does its occurrence compare to natural selection?

A mutation is an error in DNA replication that provides the raw material for evolution. Underlying mutations are random, whereas natural selection is non-random.

What four types of point mutations alter DNA sequences?

Substitution, deletion, insertion, and inversion.

What is the difference between a missense mutation and a silent (neutral) mutation?

A missense mutation alters the resulting protein and affects the phenotype, whereas a silent mutation does not change the amino acid sequence or phenotype (for example, both $GAG$ and $GAA$ code for glutamic acid).

What specific point mutation in the beta-globin gene causes sickle cell anemia?

A missense point mutation changes the DNA sequence from $GAG$ to $GTG$ (RNA $GAG \rightarrow GUG$), substituting glutamic acid ($Glu$) with valine ($Val$).

What are microsatellites?

Non-coding DNA regions containing tandem repeats of $2$, $3$, or $4$ nucleotides.

What did Bridgett M. vonHoldt et al. (2016) discover about the genetic origin of the Great Lakes wolf (Canis lycaon) and Red wolf (Canis rufus)?

Whole-genome sequence analysis showed that both are admixed hybrid lineages derived from hybridization between the coyote (Canis latrans) and the gray wolf (Canis lupus).

Which two species hybridized to give rise to cultivated chili and bell peppers, and how many wild pepper species exist?

Cultivated chili and bell peppers originated from hybridization between Capsicum annuum and Capsicum frutescens; only $5$ species of wild peppers exist.

What is an ecotype?

A genetically differentiated population within a species that exhibits geographic phenotypic variation adapted to local environmental conditions.

What three evolutionary mechanisms can reduce genetic variation within a population?

Genetic drift, the founder effect, and population bottlenecks.

What is genetic drift, and in what type of population is it most influential?

Changes in allele frequencies through random variation in birth and death rates due to chance events; it has a stronger effect and leads to faster allele fixation in small populations.

What is the founder effect?

The colonization of a new area (such as an island) by a small number of individuals, leading to low genetic diversity in the established population.

What is a population bottleneck, and what are its genetic consequences?

Continued existence as a small population following a catastrophic crash, which causes severe loss of genetic diversity through accelerated genetic drift and inbreeding.

What degree of genetic diversity is shared among cheetahs as a consequence of historical population bottlenecks?

Cheetahs share $99\%$ of their genetic diversity, creating extreme uniformity that presents significant conservation risks.

How did mitochondrial haplotype networks differ between Volcano Alcedo and Volcanoes Cerro Azul and Sierra Negra in Galapagos tortoises?

Volcano Alcedo ($3{,}000\text{--}5{,}000$ tortoises) was dominated by a single widespread ancestral haplotype following a bottleneck, whereas Volcano Cerro Azul ($400\text{--}600$ tortoises) and Volcano Sierra Negra ($100\text{--}300$ tortoises) maintained diverse, branching haplotype networks.

What is the formula used to calculate the population genetic differentiation statistic $F_{ST}$?

$$F_{ST} = \frac{\text{variation between populations} - \text{variation within populations}}{\text{variation between populations}}$$

In the meta-analysis by Diana Gamba and Muchhala (2020), which five factors were examined to evaluate their impact on seed plant population genetic structure ($F_{ST}$)?

Mating system, growth form, pollination mode, seed dispersal mode, and latitudinal region ($N = 337$ seed plant species).

How does pollination mode affect genetic structure across distance in cloud forest plants according to Gamba and Muchhala?

Insect pollination restricts gene flow to shorter distances, resulting in a steeper decline in kinship with distance (higher genetic structure), whereas hummingbird pollination facilitates longer-distance pollen dispersal, sustaining higher gene flow and shallower kinship decline.

Which paired insect-pollinated and hummingbird-pollinated plant species were evaluated by Gamba and Muchhala in Ecuador?

Gesneriaceae: Drymonia brochidodroma (insect) vs. Drymonia tenuis (hummingbird); Melastomataceae: Ossaea micrantha (insect) vs. Meriania tomentosa (hummingbird); Rubiaceae: Notopleura longipedunculoides (insect) vs. Palicourea demissa (hummingbird).

What is the biological definition of sexual reproduction?

The fusion of male and female gametes to form a diploid zygote.

What is recombination via crossing over?

The process where pieces of DNA are broken and combined to produce new combinations of alleles.

What is vegetative reproduction?

A form of asexual reproduction involving the production of new individuals through growth.

Which plant species is pictured demonstrating vegetative reproduction by growing plantlets where its arching fronds touch the soil?

Walking fern (Asplenium rhizophyllum).

What is parthenogenesis, and what animal group was noted where some species are $100\%$ female?

The development of an embryo from an unfertilized egg; Whiptail Lizards.

What is selfing in plants?

A process where a plant's pollen fertilizes its own ovules.

What is the "cost of meiosis" in sexual reproduction?

Parents contribute only half the number of genes ($50\%$) when reproducing sexually compared to asexual cloning, which evolutionarily halves their fitness contribution to the next generation.

Besides the cost of meiosis, what other costs are associated with sexual reproduction?

The costs of finding and attracting mates, performing courtship displays, growing secondary sexual characteristics (such as a peacock's tail or floral displays), and producing specialized reproductive systems (such as gonads).

What are the two major evolutionary benefits of sexual reproduction?

1) The ability to purge deleterious mutations that accumulate across clonal generations, and 2) generating genetic diversity to cope with changing abiotic and biotic environments.

What does the Red Queen hypothesis propose about sexual reproduction?

Sexual reproduction aids organisms in an evolutionary arms race against pathogens because genetically variable offspring act as a "moving target" that is less susceptible to specialized parasites.

Why do resource limitations affect male and female reproductive success differently?

Female function produces larger gametes (fewer overall) and is limited by available resources to produce eggs and raise offspring. Male function produces smaller gametes (more overall) and is primarily limited by mating access to eggs.

How do simultaneous hermaphrodites differ from sequential hermaphrodites in animals?

Simultaneous hermaphrodites perform male and female functions at the same time (e.g., snails, worms), while sequential hermaphrodites change sex over time, either male first (molluscs, echinoderms) or female first (some fishes).

What is the difference between dioecious, monoecious, and perfect floral structures in plants?

Dioecious plants have separate male and female individuals; monoecious plants have separate male and female flowers on the same plant; and perfect flowers contain both male and female organs in the same flower (hermaphrodites, representing roughly $\frac{2}{3}$ of plants).

What are the primary reproductive roles of the stigma and anthers in a flower?

The stigma is the female receptive organ, while the anthers are the male pollen-bearing organs.

What three mechanisms allow plants with perfect flowers to prevent selfing?

Self-incompatibility, sequential hermaphroditism, and heterostyly.

Why does the rarer sex typically have a fitness advantage in a population?

Because members of the rarer sex have higher average mating success and transmit a greater number of gene sets per individual to the next generation compared to members of the common sex.