Big ecology questions:

1. What factors determine distribution and abundance of organisms ?

2. What limits and regulates populations ?

3. How will organisms, ecosystems or the planet respond to changes in climate, land use, or other biota (extinctions, invasions, changes in traits) ?

Niches (a la Hutchinson’s 1957 “hypervolume”)

• Niche: the limits, for all important environmental factors (conditions and resources), within which individuals of a species can survive, grow, and reproduce

– Fundamental Niche: : The largest ecological niche an organism or species can occupy in the absence of adverse biotic interactions

– Realized Niche: The portion of the Fundamental Niche occupied by a species subject to adverse biotic interactions

Resources, conditions, and the fundamental niche

• What determines the distribution and abundance of species?– In part, their tolerance of conditions,

and their need for certain resources *condition: abiotic environmental factor that varies in space and time and affects the performance of organism

**resource: all things consumed (used up) by organisms (space, nutrients, water, prey, holes for refuge, etc)

Performance is generally nonlinear across a range of intensities of an abiotic condition: more is good, even more is bad…

Condition (e.g., temperature)cold hot

Performance of species

Reproduction

Growth

Survival

s sg gr r

Homeostasis harder to maintain when organism is further outside of its favorable range.

A resource can become a condition at high or low levels, e.g., light, oxygen, water.

Distributions of organisms determined by co-occurrence of a number of critical (potentially limiting) resources and conditions:

Soil moisture

Light grows

dies

Nitrogen

Light grows

dies

Phase diagramsBTH Fig 2.2b

Temperature

Salinity

Fresh 0 ppt

Salt, 30 ppt

Withoutparasite

Stickleback Fundamental Niche

Tolerates more salinity at colder temperatures

Tolerates warmer temperatures at lower salinity osmoregulatory

“stress”—fish spends metabolic energy to avoid water loss through gills, so has less energy to spend on other life functions (e.g. reproduction)

cold warm

Sticklebacksurvives, grows

Temperature

Salinity

Fresh 0 ppt

Salt, 30 ppt

Realized Nichewith gill parasite, tolerates narrower range of conditions

Withoutparasite

Realized stickleback niche if gill parasite is present.

H1. Gills damaged so can’t osmoregulate as efficientlyH2. Parasites more abundant under warmer or more saline conditions

Degree days for ectotherms (BTH p. 33)

• For each 10oC rise in temperature, rate of biological enzymatic processes often roughly doubles, until enzymes denature (Q10 = 2)

• When growth or development increases nearly linearly with temperature, “degree-days” rather than days predict phenology (seasonal progression of biological events—bud burst, insect emergence, etc.)– With a physiological threshold = 10oC, mite takes 24 days to

develop at 15oC, and 8 days at 25oC. Development requires 120 degree-days above threshold at both temperatures.

% development completed day-1

0

0.1

0.2

10 20 30

Wessels 1997: “For the southern boundary, I have traced a line where the proportions of eastern red cedar to common juniper in old pastures is roughly equal….the change in species is due to decreasing winter temperatures, to which the upright red cedar is less tolerant.”

Time dependencies

• Acclimatization (“acclimation in the lab): shifts in the response of an organism to a condition caused by the regime it has experienced in the past.– E.g. trees can tolerate lower temperatures in

October than they can if surprised in mid-summer, because they’ve induced new types of proteins and restructured cell membrane phospholipids.

• Are organisms limited by the maximum level of a condition, or by whether it lasts a certain period of time?– Crayfish or starfish displaced by short bursts of

fast flow, but if current increases gradually, may hunker down and hold on

– Saguaro cacti can tolerate freezing if there is a daily thaw, but can’t take it if freezing temperatures last more than 30 hours.

Velocity (cm s-1)

Depth (cm)

Boundary layer

Free-Streamvelocity

Surface dragsurfaceSize dependencies

bed

Reynolds Number:

(Flow velocity x Object diameter)/ kinematic viscosity of fluid

High values—turbulence and form drag matterLow values---viscosity and friction drag matter

Vogel (1981) Life in moving fluids

Biomechanics at Berkeley: Mimi Koehl, Bob Full

Neritic: nearshore subtidal

Benthos: life on substrate or bed of sea, lake, spring, or rivers and streams

Plankton: passive driftersNekton: active swimmers

zooplankton

phytoplankton

Stoichiometry(Sterner and Elser 2002)

• Study of balance of energy and multiple chemical elements in living systems

• Redfield Ratio (atoms): C (106): N (16): P(1)

• Plants: C:N and C:P generally higher than in animals (varies among taxa, tissues, age groups)

• Detritus even worseRedfield Ratio

Plant C:N:P Ani

mal

C:N

:P

Sterner and Elser 2002

Animals show more strict stoichiometric homeostasis than plants

Problem for herbivores anddetritivores: to get enough N and P

Supplemental reading Chapin, F. S., III, and G. R. Shaver. 1985. Individualistic growth response of tundra plant species to environmental manipulations in the field. Ecology 66:564-576. Chapin, F.S., III. l980. The mineral nutrition of wild plants. Annu. Rev. Ecol. Syst. ll:233-260 Sterner, R. W., and J. J. Elser. 2002. Ecological Stoichiometry: The biology of elements from molecules to the biosphere. Princeton University Press, Princeton NJ. Thompson, D. A. 1942 (1917). On Growth and Form. Cambridge Univ. Press, Cambridge, UK. Vogel, S. 1981. Life in moving fluids. Princeton Univ. Press, Princeton, N.J. Web sites: http://cbc.berkeley.edu/thisweek.html (seminar postings) http://bie.berkeley.edu/index.htm (Berkeley Institute of the Environment)