Eco - Diversity + Climate Change

Species Richness

The number of different species present in a community

A simple count …

Does not consider the abundance of differences in species richness

Species richness must be…

Different species, not number of individuals.

Species Richness Example

Forest with 10 species of tress has greater richness than one with 5 species.

Equitability (Evenness)

How individuals are distributed among the species present

If one species makes up 90% of individuals…

Evenness is low

If all species have roughly the same number…

Evenness is high

High diversity

Many species (high richness) and grow in roughly equal abundance (high evenness)

High Diversity Example

Coral reefs, tropical rainforest

Shannon Index (H’)

Ranges from 0 to infinity

Shannon Index Equation

H’ = −Σ (𝑝𝑖ln𝑝𝑖)

Pi =

proportions of individuals in X species

Higher H’ =

Higher diversity

Shannon Index Equation is sensitive to…

Both evenness and richness

Typical value of low diversity

~0.5, polluted stream

Typical value of moderate diversity

~1.5-2.5

Typical value of high diversity

>2.5, rainforest

Simpsons (D) Index Equation

𝐷 = Σ(𝑝2 𝑖)

D =

Dominance, higher D = lower diversity

P =

proportions each species makes up

Simpsons (D) Index

If one species dominates (90%), D will be close to 1 (low diversity). Ranges from 0 to 1.

Where diversity is the highest

Topics, mountains, offshore oceans

Where diversity is the lowest

polar regions, deserts

Diversity patterns are consistent across what taxa?

Plants, animal, microbes

Habitat diversity

More types of habitat, more niches

Habitat diversity example

Mountains have many different zones of temperature and moisture, which creates many micro habitats and niches

Habitat Diversity - History of Europe

Fewer tree species due to repeated glaciations. Mountain ranges run east to west, which can block migration patterns.

Habitat Diversity - History of North America

Mountains run north-south, allows easier migration

Why are over half of all species occurring in ~1% of Earth’s land (tropical regions)?

Time and area, tropical conservatism, productivity, spatial heterogeneity, evolutionary time, evolutionary speed, climatic stability, intermediate disturbance

Time and Area Hypothesis

Topics historically covered a large, stable area - allowed species to persist and diversify. Lower extinction.

Tropical Conservatism Hypothesis

Tropical species tend to stay in the tropics, temperature species evolved later and moved in. Increase Accumulation.

Productivity Hypothesis

High sunlight and rainfall - high primary productivity - more food and anergy. Increase Trophic levels.

Spatial Heterogeneity Hypothesis

Wide range of micro habitats (light, temp, moisture), especially in mountains. Increase Niches

Evolutionary Time Hypothesis

Tropics are ancient - specie shad longer to evolve and specialize. Increase Speciation

Evolutionary Speed Hypothesis

Warmer temperatures and stable climates - faster mutations and evolution rates. Increase speciation.

Climatic Stability

Stable climate - species can finely tune to niches, decrease extinction. Increase persistence.

Intermediate Disturbance Hypothesis

Moderate, periodic disturbance (e.g., droughts, floods, tree falls) present competitive exclusion, promote turnover. Increase diversity.

Time and Area - Long-term stability and large continuous areas

Promote speciation

Time and area - greater tropical areas in the past…

Allowed large species ranges and less extinction

Time and Area - larger areas =

More individuals and greater genetic variation

Conservatism - many species originated in..

The tropics and never left.

Conservatism - Adaptations…

To warm, west climates make it hard to colonize temperate regions

Conservatism - most lineages live near…

Their evolutionary origins

Productivity

More sunlight and more rainfall in tropical areas allow for more plant biomass

Productivity - increaseD photosynthesis

High primary productivity supports more complex food webs, abundant food means less extinction risk and allows more individuals to be able to coexist.

Spatial herterogeneity

Variation in habitat (light, temperature, moisture) provides many niches

Spatial Hetergeeity - Mountains and rainforests

On mountains when variation occurs as elevation increase. Rainforests allow different niches depending on location in canopy layer.

Spatial Heterogeneity - Variation prevents…

One species from dominating