Organisms and Populations

Ecology is study of organisms and their environment. Environment has abiotic non-living and biotic living factors.

Abiotic = Temperature, Water, Light, Soil.

Temperature: Most important. Stenothermal narrow range tolerance like arctic moss, coral. Eurythermal wide range like humans, carp, cockroach. Temperature affects metabolism, enzyme activity.

Water: Second most important. Desert needs adaptations to conserve water. Productivity limited by water.

Light: Sun is energy source. Light zonation - photic bright, twilight dim, aphotic no light. Photoperiod affects flowering, migration.

Soil: pH, minerals NPK Ca Mg, texture, water holding determines plants. Edaphic factors.

How organisms handle stressful abiotic? Four ways:

Regulate: Maintain constant body temp/osmolarity like birds mammals 37C, sweat shiver. Most constant homeostasis.

Conform: Body temp changes with environment - 99% animals and all plants conformers. They cannot regulate, so they conform.

Migrate: Move away temporarily - birds migrate Siberia to Keoladeo, Arctic tern longest migration.

Suspend: Stop metabolism - hibernation winter sleep bear, aestivation summer sleep snails fish, diapause zooplankton in lakes, spores seeds bacteria form thick wall to survive.

Adaptation is morphological physiological behavioural feature to survive.

Kangaroo rat desert: Never drinks water, makes water from internal fat oxidation, concentrated urine, nocturnal.

Desert plants: Thick cuticle, sunken stomata, CAM photosynthesis, leaves reduced to spines in cactus.

Altitude sickness: High altitude low oxygen, body makes more RBC, haemoglobin, breathing rate increases. At 3500m you feel nausea, heart racing. Adaptation over time in Ladakh.

Allen's rule cold: Mammals in cold have shorter ears limbs to reduce heat loss - polar bear small ears. Blubber thick fat in seals for insulation.

Population = group of same species in area. Attributes:

Birth rate natality: Number of births per 1000 per year.

Death rate mortality: Number of deaths per 1000 per year.

Sex ratio: Males per 100 females, e.g. 105 males 100 females typical.

Age distribution pyramid: Young 0-14, Adults 15-64, Elderly 65+. Expanding pyramid broad base many children rapid growth, Stable bell shaped even distribution, Declining urn narrow base low birth rate aging population.

Growth depends on resources.

Exponential J curve: Unlimited resources food space infinite, growth equation Nt = N0 e^rt where N0 initial, r intrinsic rate, t time, e base. J shaped, fast growth like bacteria.

Logistic S curve: Limited resources, carrying capacity K maximum population environment can support. Equation dN/dt = rN (K-N)/K Verhulst-Pearl logistic. S shaped with lag, log, stationary. As N approaches K, growth slows. Human growth logistic.

r-selected fast reproduce small many offspring like insects, K-selected slow few offspring care like elephants humans.

Species interact in community.

Mutualism ++ both benefit: Lichen algae fungus, Mycorrhiza fungi + plant roots, Fig + wasp, Pollination.

Competition -- both harmed: Flamingo vs fish same food, Abingdon tortoise extinction due to goat competition, competitive exclusion Gause - two species competing same resource cannot coexist, resource partitioning.

Predation +- one benefits one harmed: Predator eats prey. Keeps prey population control, energy transfer. Adaptations: camouflage, chemical poison monarch butterfly cardiac glycosides.

Parasitism +- parasite benefits host harmed: Cuscuta dodder plant parasite, human lice, brood parasitism cuckoo lays eggs in crow nest.

Commensalism +0 one benefit other no effect: Orchid growing on mango, barnacles on whale, cattle egret and grazing cattle.

Amensalism -0 one harmed other no effect: Penicillium fungus kills bacteria by penicillin, black walnut tree toxic to other plants.