besc 201, introduction to bioenvironmental sciencepeople.tamu.edu/~tdewitt/wfsc304/8. wfsc 304...

Introduction to Wildlife & Fisheries ConservationWFSC 304

Lecture 4: Ways to measure biodiversity

Upshot from last time: Understanding the new view of speciation, termed “ecological speciation”, we also understand how adaptive radiations take place:

I told you about African rift lake cichlids: Book example (Hawaiian honey-creepers):

Adaptive radiation: rapid evolution of form to fit newly open niche space, either following a key trait innovation or formation of new niches per se.

Good figure on VT = VG + VE concept: The first is called a “common garden” experiment

Measures of diversity• Richness (R = number of “types”; e.g. genotypes, phenotypes, species)• Evenness• Diversity indices

Wikipedia: A diversity index is a quantitative measure that reflects how many different types (such as species) there are in a dataset and simultaneously takes into account how evenly the basic entities (such as individuals) are distributed among those types. The value of a diversity index increases both when the number of types increases and when evenness increases. For a given number of types, the value of a diversity index is maximized when all types are equally abundant.

Those are useful metrics, but should all species be counted equally? Is a community not more diverse if it contains otherwise rare species, like endemics or endangered species?

• Endemism (proportion of species endemic)

• Rare/Threatened/Endangered species

• Functional diversity Locally endangered: Navasota ladies’ tresses

• Phylogenetic diversity Spiranthes parksii• Taxonomic • Deep lineages (branch lengths)

• Alpha/Beta/Gamma diversity:

• Genetic diversity

• Commonly characterized by FST using molecular genetic variation.• FST is the proportion of genetic variance among subpopulations, VS,

relative to total variation, VT.• This is entirely analogous to h², genetic variance among families relative

to total.• Like h², FST values range from 0 to 1.• High FST indicates strong differentiation among populations• A related concept is FIS, the inbreeding coefficient, in which variation

within individuals (i.e. heterozygosity) is expressed as a proportion of that at the subpopulation level. High FIS implies a lot of inbreeding.

• You should see a strong theme in all these measures—nested levels of genetic variation: within individuals, within families, within subpopulations, within the full population—like Russian nesting dolls.

FST = how different are subpopulations?

Scenario 1

2

3

In the bottom case, all variance is among subpopulations (no variance among individuals). So FST = VS/ VT = 1

Patterns on the landscape• Latitude, longitude, altitude

(e.g. Bergmann’s Rule)

• Landform• Vicariance (population separation or

reduced geneflow due to physical or environmental barriers—mountain ranges, major rivers, hypoxia)

• Insular effects—e.g. endemism, dwarfism (Florida panther), or gigantism (island chuckwalla)

• Area (cumulative species/area curve)• Can use this to find hotspots • Energy• Regional richness • Taxonomic

covariance

Biodiversity at alternative scales

(you do not need to know these distinctions—take the lesson conceptually that major habitat patterns change globally, often roughly latitudinally, though the species present on different continents will differ)

EcoregionsA relatively large area containing a distinct assemblage of natural communities and ecological conditions, characterized by a dominant and widespread assemblage of species

Post oak savannah Pineywoods Hill country

When you see a map, find the patterns and reflect.

What is causing changes in major plant communities moving east-west, north-south, etc.?

What other influences are evident?

Biodiversity is unevenly distributed globally

Conservation Biology is a spatial science. In deciding where we should work, it is important to note that biodiversity is not evenly distributed across the planet. It is heavily concentrated in the tropics, with decreasing species richness as one moves towards the poles. In this map, which represents a combined species richness map for all mammals, all amphibians, and all threatened birds, regions of dark red correspond to areas of higher richness; dark blue to regions of lower richness. Source: Modified from Baillie et al. (2004) Global Species Assessment. IUCN

Common reasons given why the tropics should be so speciose:

1. More energy in2. Long history of environmental

stability (e.g. lack of glaciation)3. Warm temperature and

high humidity conducive to growth of producers

4. Predictable environment leading initially to greater competition

among lineages but ultimately niche differentiation

S= speciesG=generaF= families

Note the pattern for mollusks—how do these data fit the ideas enumerated above?

“Population reconstructions for humans and megafauna suggest mixed causes for North American Pleistocene extinctions”

Jack M. Broughton  & Elic M. Weitzel 

Nature Communications volume 9, Article number: 5441 (2018) 

Abstract

Dozens of large mammals such as mammoth and mastodon disappeared in North America at the end of the Pleistocene with climate change and “overkill” by human hunters the most widely-argued causes. However, the population dynamics of humans and megafauna preceding extinctions have received little attention even though such information may be telling as we expect increasing human populations to be correlated with megafaunal declines if hunting caused extinctions. No such trends are expected if climate change was the primary cause. We present tests of these hypotheses here by using summed calibrated radiocarbon date distributions to reconstruct population levels of megafauna and humans. The results suggest that the causes for extinctions varied across taxa and by region. In three cases, extinctions appear linked to hunting, while in five others they are consistent with the ecological effects of climate change and in a final case, both hunting and climate change appear responsible.