Unit 10 - Species, Adaptations, and Niches

“The growth or distribution of a species is dependent on the one environmental factor most critically in demand” 

• justus von liebig

The law of the minimum

Each plant species is able to exist and reproduce only within a definite range of environmental conditions

Theory of tolerance

A ___ consists of groups of genetically, morphologically, and ecologically similar natural populations that may or may not be interbreeding but that are reproductively isolated from other such groups.

species

An ___ is a portion of the overall species that is adapted to a specific habitat or environment

Ecotype

An ____ is a continuum in the variation of a species associated with an environmental gradient

Ecocline

A ____ is the n-dimensional hypervolume in defining the environmental limits within which an organism is able to survive and reproduce

Niche

No two species can coexist permanently in the same niche

I.e. if two competing species coexist in a stable environment, they do so as a result of niche differentiation

In the absence of niche differentiation, coexistence is not possible

Gause’s Principle of Competitive Exclusion

Niche concept was originally developed by zoologists (Elton and Grinnell) for animals

habitat and food defines the niche of a species

E.g., differences in diet, foraging patterns, etc

All plants require the same (or similar) resources

Water

Light

CO2

N, P, K, and small and common set of micronutrients

And plants are (mostly) immobile

But there only ___ biochemical pathways for carbon acquisition (two of which have evolved repeatedly)

three

_____ occurs in only 10 families (out of 380 families and perhaps over 420,000 species)!

And these 10 families are closely related

N fixation by symbiotic bacteria

Therefore, there must be ____ on the evolutionary scope for diversification in plant resource acquisition

severe constraints

Different species are adapted to ____

different conditions

Environments are ___ in space and time.

heterogeneous

Rooting depth for temperate grasses

Rooting depth for shrubs and herbs in deserts

Hydrological gradients for meadow plants

Nitrogen source for arctic herbs

Topography in tropical forests

Belowground:

Light environment

Canopy height

Light intensity

Exploitation of gaps

Carbon acquisition

Temperature tolerance

Herbivory tolerance

Aboveground:

There are over 420,000 seed plants...

And > 30,000 defensive compounds have been discovered in plants...

biochemistry