Ecological Conditions

Summary of the effects of conditions on species distributions

• Lethal conditions may limit distributions but they only need to occur occasionally in order to do so.

Saguaro cactus in snow

Summary of the effects of conditions on species distributions

• Distributions are more often limited by conditions that are regularly suboptimal (rather than lethal) leading to a reduction in growth or reproduction or increased chance of mortality.

Click beetle on snow

Summary of the effects of conditions on species distributions

• Suboptimal conditions often act by altering the outcome of a biological interaction between the species of interest and other species.

St. John’sWort – aka Klamath weed

Distribution of St. John’s Wort in North America

Key: dark blue – present in state; light blue – present in county;pink – noxious weed

Chrysolina Beetles on St. John’s Wort

Summary of the effects of conditions on species distributions

• Suboptimal conditions often interact with other conditions so that it is often impossible to locate a single condition as the most important factor.

Mediterranean fruit fly

Summary of the effects of conditions on species distributions

• Suboptimal conditions are often moderated by the evolutionary, physiological and behavioral responses of the organisms.

Kangaroo Rat

Summary of the effects of conditions on species distributions

• Towards the edge of a species range, it occupies patches in which conditions are closest to those found in the center of its range.

Rufous grasshopper

Rufous grasshopper habitat

• The rufous grasshopper is usually found in open land, particularly terrain such as meadows, pastures, and forest edges that feature tall grass. More specifically, it can often be found in chalk grassland. It has been found on southern slopes of the Alps up to approximately 8100 feet. It prefers warm environments of moisture levels ranging from dry to moist.[3] Very common locations include regions of Europe, including Germany, Sweden, France, and the United Kingdom. In fact, it can be found across almost all of Europe and Asia, ranging from France to parts of Siberia and from Scandinavia to northern Germany.

• http://en.wikipedia.org/wiki/Rufous_Grasshopper

Relative Humidity

• Relative humidity - is a measure of the amount of moisture in the air

• all terrestrial organisms must conserve water and prevent water loss to surrounding environment - in general the higher the relative humidity (the amount of water contained in the air) the less energy an organism has to expend to conserve water

Transpiration

Joshua Tree – Xerophyte – grow in dry habitats

Water lily – Hydrophyte – grow in wet habitats

Hepatica – Mesophyte – grow in moist habitats

True Xerophyte leaf - Oleander

Barrel cactusSucculent

Desert Ephemerals – South Africa

Desert soil profile – Phreatophytes with deep root systems

Soil pH

• plants suffer direct toxic effects when soil pH is below 3 or above 9 - there are naturally occurring soils which have these pH's

• However at more moderate pH there can be indirect effects

Salinity

• For aquatic organisms the concentration of salt in the water presents a condition that limits distributions

salinity gradient in an estuary

Pollution

Pollution - unfortunately this is becoming a condition which species must respond to

1.Toxic effects - heavy metals in soils, often from mine tailings, are deposited onto soil in high concentrations

2. Acid precipitation

Bent grass –Agrostistenuis

Acid precipitation

• Acid precipitation acts by:• 1) directly by upsetting osmoregulation - water

balance, enzyme activity or gas exchange, • 2) indirectly by increasing toxic heavy metal

pollution concentrations by leaching them from the soil - especially Aluminium,

• 3) indirectly by reducing the quality and range of food resources available to animals - plants grow less well

Trees Burnt by Acid Precipitation – Northeastern U.S.

Resources

• Resources are parts of the physical environment that are consumed (used up) by living organisms – There are many different resources –

• For plants – solar radiation, soil nutrients, water, carbon dioxide, space

 • For animals – primarily food sources, oxygen, space

 • For decomposers – a supply of dead organic matter,

oxygen (for some), space

The Niche

• ecological niche - the way in which an organism interacts with all of the biotic and abiotic factors in its environment - often described as how the organism makes its living, its functional role, but includes the habitat it occupies

Niches in European seed-eating birds

Common redpoll Linnet

Greenfinch Hawfinch

Precursors to theory of the niche:Liebig’s law of the minimum 1840

Precursors to theory of the niche:Shelford’s law of tolerance

• The distribution of a species is controlled by the environmental factor for which the species has the narrowest tolerance.

G. Evelyn Hutchinson age 18

Hutchinson’s Niche Definitions

• The fundamental niche - the set of resources and conditions that permits the survival and reproduction of an organism - many resources and conditions interact to form the niche.

• The realized niche - the portion of the fundamental niche actually occupied by the species when restricted by other organisms - restricted by competition, predation, parasites, disease.

- Hutchinson 1958

Fundamental vs. Realized Niche

N-dimensional niche

Key point – two species cannot have identical niche