Lecture 2: Global Biodiversity: How Natural Patterns Inform Conservation

Gonzalez

Estimates for the number of eukaryotic species on Earth

• 3-100 million

• ~8.7 million ( ± 1.3 million) eukaryotic species

• ~2.2 million are marine

Estimates for percentage of species still awaiting descriptions (Earth and Ocean)

• 86% on land

• 91% in the ocean

Why are there fewer described ocean species?

• There is lower relative diversity in marine habitats (excluding coastlines).

Percentage of life in soil

• 59%

• Most biodiverse habitat on Earth

Species Richness

• Number of Species

Evenness

• Distribution of species and their balance

Species discovery/ accumulation curve

• Number of species discovered depends on effort invested

Rank - abundance curve (and changes in RAC)

• Changes can indicate how evenness is changing, loss of species, introduced species, reordering of species dominance

• These changes require effort to detect, which most countries simply do not have the resources for.

Log RACs - how to interpret them

• Slope indicates evenness

• Steep gradient= low evenness

• Shallow gradient= high evenness

Species Abundance Distributions (SADs)

• Plot of the frequency relative to their abundance

GBIF - Global Biodiversity Information Facility

• From 1900, SAD has become more lognormal because of citizen science/ research

• There may be universality in the shape of the SAD (though some groups have more or less of the SAD discovered)

Biodiversity hotspots

• Geographically defined areas that have an extraordinary concentration of endemic species

• More than half of Earth’s species contained in 1.4% of its land area

• Currently 36 recognized hotspots

Percentage of vascular plant species found in biodiversity hotspots

• 44%

Percentage of vertebrate species found in biodiversity hotspots

• 35%

Criteria for biodiversity hotspots

High endemism: 

• Must contain at least 1,500 species of vascular plants that are found nowhere else on Earth

Significant threat:

• It must have lost at least 70% of its original habitat

How hotspots emerged

• Topographical and microclimate diversity

• Macroclimate stability

Proportion of hotspot species at high extinction risk 

• 2/5

• 1/3 because of increasing climate change in previously stable microclimate

• Species can’t adapt fast enough

The Latitudinal Diversity Gradient

• High number of mammals in tropical latitudes (and most other groups)

• There are some exceptions (salamanders)

• This pattern holds true for elevation gradients as well

• Has flattened during “greenhouse” periods (higher global temperatures)

Groups for which the Latitudinal Diversity Gradient holds true

• Vascular plants

• Birds

• Mammals

• Amphibians

• Mosses

Three hypothesis groups for LDG

1. Climate and energy hypotheses  

2. Historical/ Evolutionary hypotheses

3. Spatial hypotheses

Climate and energy hypotheses for LDG

• Species - Energy: More solar energy and water in the tropics leads to higher productivity

• Climatic Stability: Less seasonality allows for greater specialization and narrower niches

Historical/ Evolutionary hypotheses for LDG

• Evolutionary time: never scoured by glaciers, so “more time” to develop

Spatial Hypotheses for LDG

• Mid-domain effect

• Ranges overlap at the equator