Interactions with the environment. AH Biology Environmental Biology

Interactions with the environment All organisms must be able to make internal adjustments in response to external changes in conditions External – constant flux Internal – range that must not be exceeded. Organisms responses Resist or tolerate Regulation (homeostasis) Avoidance / migration

Behavioural responses Changes in an organism’s behaviour which help them to survive changes in their environment. Examples Desert mammals Nocturnal Live in burrows during day Hibernation or migration to avoid low temperatures

Physiological responses Changes in a way an organism’s body functions to enable it to survive in changing circumstances. Organism can show a certain tolerance to its environment Homeostasis

What the specification says! Interactions with the environment AH Biology

Responses Two major types of responses of organisms to variation in environmental conditions Conformation regulation.

Conformation Conformation Tolerance and resistance. osmoconformers poikilotherms. Tolerance and resistance. Restricted habitat occupation of conformers.

Dormancy Dormancy as a means of resisting or tolerating environmental adversity. Predictive and consequential dormancy. Forms of dormancy: resting spores, diapause, hibernation, aestivation.

Regulation homeostatic control in regulators as illustrated by osmoregulators and homeotherms. The ability of regulators to occupy a wide range of habitats. Energy costs of homeostasis.

Variations in Life Histories Life history of an organism comprises its patterns of growth, development and reproduction.

Growth and development Rapid development Leads to early reproduction and high rates of population increase Periods of arrested development Extend life cycle through periods of adverse environmental conditions Longevity Species with multiple breeding seasons

Reproduction Alternation of generations “trade-off” reproduction and survival of parent Some organisms reproduce once in a lifetime Others have reproductive episodes through life Clutch size Large Organisms who are unlikely to survive until the next season Small Organisms with a high probability of survival

Life Histories K-strategists (K-selected) r-strategists (r-selected) Development Slow Rapid Adult Size Large Small Number of Offspring Few and large Many and small Generation time Long Short Extra information Limited by K Live in stable environments (Climax community) Opportunistic species, fluctuating environments (pioneers)

Survivorship Curves

Survivorship curves Type I Type II Type III flat during early and middle life and drops suddenly as death rate increases among the elderly. This type of survivorship curve is associated with species such as humans and other large mammals that produce few offspring that are well cared for. Type II intermediate, with mortality more constant over life spans. This type is seen in Hydra and the grey squirrels Type III very high death rates for the young, followed by lower death rates. This type is often associated with organisms, such as oysters, that produce very many offspring but provide little or no care.

Dormancy Dormancy is a life history stage Resting or tolerating periods of environmental adversity Predictive (P) Consequential (C) Physiological state of minimal metabolic activity allowing an organism to avoid poor conditions or food shortages Facultative obligate

Forms of dormancy Resting spores (C) Diapause (P) Hibernation (P or C) Survive harsh conditions Diapause (P) Suspended development in insects Hibernation (P or C) Inactivity in mammals associated with cold winter conditions or food shortages Aestivation (C) Inactivity in hot, dry periods State of torpor Reduction of body temp. to ambient temp

Homeostasis Negative Feedback

Homeostasis The process of maintaining stable internal environment When the external environment varies there are two basic patterns of response Conformation Internal variables fluctuate with external environment Limited environmental range Regulation Internal variables maintained at a constant level Requires considerable energy Less affected by environmental conditions

Osmoconformers Poikilotherms Conformation Osmoconformers Poikilotherms

Osmoconformers Isosmotic (body tissues are isotonic with sea water) Do not alter internal solute concentration No osmotic gradient

Poikilotherms Variable internal temperatures Animals obtain body heat from the environment (ectotherm)

Ectotherm

Endotherm and ectotherm

Osmoregulation Homeotherms

Osmoregulation Body fluids not isotonic with the environment. Use energy to regulate internal osmolarity Revise Higher Biology SW and FW fish in hypotonic or hypertonic environments Revise kangaroo rat, and adaptations of xerophytes

Homeotherms Relatively stable, raised internal temperatures Revise human temperature regulation from higher biology Endothermy carries an energy burden that opens up niches for foraging.

Essay Question Give an account of homeostasis, discussing the differences between regulators and conformers.