2.1.II - Keystone Species & Biodiversity

Ecosystem Diversity

" A self-contained community of microorganisms, animals and plants, that interact with each other and with their physical environment."

2 Components that determine the Species Richness in an ecosystem...

1. The abundance of potential ecological niches More complex communities (i.e. greater biodiversity) provide more niches and vice versa for different organisms to exist in 2. Proximity to the margins of adjacent ecosystems Transitional zones where multiple ecosystems meet (ecotones) will contain most of the niches Species can take advantage of more than one habitat in a short distance Leads to increase in # of species present in an area

Simpson's diversity index (D) is a measure of biodiversity that takes into account richness and evenness.

A high value for D (closer to 1) is 'good' and means the habitat is diverse, many niches, complex food web, species rich, and able to withstand some environmental impact. A low value for D (closer to 0) is 'poor' and means the habitat is low in species, minimal niches, simple food web, so a small change to the environment (eg. pollution) would have a serious impact.

What Are Keystone Species?

A keystone species holds a community together, when it disappears, so does the biological community. Elimination of a keystone species dramatically alters the structure and function of a community.

Nonnative species

Also called Invasive or Alien species, these can often compete with or reduce the native species.

D = 1 - [ ∑ ( n / N)2 ]

n = number of individuals N = total number of individuals

Native species

Species that normally live and thrive in the ecosystem

Indicator species

Species where a sharp decline in their population numbers often means that some factor in the ecosystem is problematic.

Keystone species

Species whose extinction or reduction can result in loss of ecosystem services for the whole community, and ultimately cause ecosystem collapse.

So, Why Should We Protect Keystone Species?

They play critical roles in their particular ecosystems. Top predator keystone species help regulate the population numbers of other species. The loss of keystone species can lead to population crashes and extinctions of other species that depend on it for ecological services. They help increase and maintain biodiversity!

Species evenness

This is a qualitative measurement It is a measurement of how close in numbers each species in an environment is.

Species richness

This is a quantitative measurement Eg "how many different species can I see?" More species does not always mean more biodiversity...why not?

Species Diversity

Variation in # of species

Genetic Diversity

Variation within population