Chapter 11 – Evolution of Organisms and Biodiversity of Freshwaters

Comprehensive practice flashcards covering measures of freshwater biodiversity, evolutionary dynamics, spatial ecology, island biogeography, population genetics, species invasions, and conservation economics from Chapter 11.

What is the difference between species richness and evenness?

Species richness is the total number of species found in an area, whereas evenness describes how equally represented the numbers of each species are.

What does the Shannon index ($H'$) measure, and under what conditions does it increase?

The Shannon index ($H'$) is a measure of diversity that includes both evenness and richness. It increases with higher numbers of species and with greater evenness.

In the formula for the Shannon diversity index ($H' = -\sum_{j=1}^{S} p_j \ln(p_j)$), how is the proportion of species $j$ ($p_j$) defined?

$p_j$ is the number of individuals of species $j$ divided by the total number of organisms in the assemblage.

Based on this Shannon diversity table comparing Pool and Riffle samples, what are the total richness ($S$), Shannon index ($H'$), and evenness ($E$) values for each sample?

For the Pool sample: $S = 4$, $H' = 1.08$, and $E = 0.77$. For the Riffle sample: $S = 6$, $H' = 1.73$, and $E = 0.97$.

What are the definitions of $\alpha$-diversity and $\beta$-diversity?

$\alpha$-diversity refers to within-habitat diversity, whereas $\beta$-diversity refers to between-habitat diversity. Together, they link spatial scale and diversity.

Comparing community groups (A)–(D) and (E)–(H), which set has lower $\alpha$-diversity but higher $\beta$-diversity?

Communities (A)–(D) have lower $\alpha$-diversity but higher $\beta$-diversity than communities (E)–(H), despite having the same total diversity and evenness.

What is the Ecoregion concept, and how many freshwater ecoregions are recognized in North America?

The Ecoregion concept uses $\beta$-diversity and abiotic conditions to classify habitats based on the diversity of fish, amphibians, crayfish, unionid mussels, and aquatic reptiles. There are $76$ ecoregions in $8$ major regions of freshwater habitats in North America.

Which $8$ of the $76$ North American freshwater ecoregions are found in Texas?

The 8 ecoregions are: U.S. Southern Plains, Ouachita Highlands, Sabine - Galveston, East Texas Gulf, West Texas Gulf, Pecos, Upper Rio Grande, and Lower Rio Grande.

What two main temporal and spatial factors influence the evolution of new freshwater species?

1. Time available for evolution
2. Reproductive isolation

What is the distinction between an endemic species and adaptive radiation?

An endemic species is one with a restricted geographical distribution, whereas adaptive radiation is the evolution of many species from a single or few founder species.

According to this comparative graph of ancient lakes, which lake is characterized by the highest number of endemic crustacean taxa?

Lake Baikal, which possesses roughly $600$ endemic crustacean taxa.

What short-term factors contribute to how many and what types of species occur in a specific environment?

Short-term factors include species interactions, productivity, species introductions, habitat type, and colonization.

What three characteristics are typical of cosmopolitan species?

1. Life history stages that can survive transport
2. Production of large numbers of individuals in the transportable life stage form
3. The ability to survive (including competing successfully and avoiding predation) in new habitats

What is the mathematical equation relating habitat area to species richness, and what do its parameters represent?

$S = c A^z$ (or $\log(S) = \log(c) + z \log(A)$), where $S$ is species richness, $A$ is the area of the habitat island, $c$ is a constant measuring species per unit area, and $z$ is the slope of the line plotting $\log(\text{area})$ versus $\log(\text{number of species})$.

How does species diversity change across the different stages of ecological succession?

Diversity is low in early succession (dominated by rapidly reproducing and widely dispersing species) and low in later succession (dominated by superior competitors that displace early colonists), reaching its maximum in the middle stages.

What is the difference between the Dynamic Equilibrium Model and the Intermediate Disturbance Hypothesis?

The Dynamic Equilibrium Model posits that disturbance decreases diversity if it exceeds recovery ability, but increases diversity if it removes dominant competitors. The Intermediate Disturbance Hypothesis relates diversity directly to disturbance frequency and intensity, predicting maximum diversity at intermediate levels of natural disturbance.

What metrics are included in genetic diversity, and why is it essential for long-term population viability?

Genetic diversity includes gene diversity (proportion of polymorphic loci across the genome), heterozygosity (number of individuals with polymorphic loci), and the number of alleles per locus. It is essential for surviving adverse periods (such as prolonged drought or climate change), disease outbreaks, and mass mortality events.

What is the ultimate source of genetic diversity, and by what mechanisms is it maintained?

Mutation is the ultimate source of genetic diversity. It is maintained by continued mutation, emigration and immigration (gene flow), and environmental variability.

What is the Minimum - Viable Population?

The lowest number of individuals required for a population to survive in the wild; below this threshold, a population cannot survive stochastic (random or chance) environmental or demographic events.

How is Effective Population Size defined?

The members of a population that actually contribute genes to succeeding generations, which can often be a small fraction of the actual total population size.

What does the concept of an Extinction Vortex describe?

It suggests that as populations become smaller, their susceptibility to extinction accelerates exponentially.

What is a metapopulation, and how does it function?

A metapopulation exists where multiple subpopulations with limited gene flow exchange individuals through dispersal, thereby enhancing and maintaining genetic diversity.

How do source populations differ from sink populations in metapopulation dynamics?

Source populations reside in prime locations where individuals survive and multiply, serving as donors that feed into other areas. Sink populations are those where individuals are going extinct but can be replenished by colonists from source subpopulations.

According to the invasive species model, what proportion of introduced species typically succeeds in establishing?

Most invaders fail to establish, with only approximately $1$ in $10$ successfully establishing (most failed invasions are never documented).

Under what community diversity conditions and trophic positions do invasive species exert the strongest ecological effects?

Major community effects occur most frequently in low-diversity systems and when the successful invader is a top predator rather than an organism occupying lower trophic levels.

What factors increase the likelihood that an invasive species will become successfully established?

Establishment is favored when native assemblages are disturbed, when species possess suitable physiological/morphological traits or a history of being invasive, and when larger numbers of invading individuals are introduced across multiple introduction events.

What is the difference between extinction and extirpation?

Extinction is a condition where no living individuals of a species exist anywhere on Earth. Extirpation is a condition where no living individuals of a species exist in the wild/natural habitat, but some may still be found in captivity.

What extent of species extinction are humans projected to cause in the next $50$ to $100\text{ years}$?

Humans will likely cause the extinction of at least half ($50\%$) of all the approximately $10\text{ million}$ species on Earth.

What is the estimated economic value of the processing of human wastes by aquatic microbes?

It is valued at more than $\$700\text{ billion}$ per year.