ecology exam 1

Energy and Nutrient Relations

• Autotrophs use energy from inorganic sources to synthesize organic compounds, enabling them to grow and reproduce.
• Heterotrophs rely on energy from organic sources, mainly consuming other organisms for growth and reproduction.

Chemoautotrophs

• Chemoautotrophs obtain energy from the oxidation of electron donors like H2, H2S, and CH4.
• Nitrifying bacteria are key chemosynthetic organisms in terrestrial ecosystems.
• These bacteria use CO2 as a carbon source and get energy by oxidizing ammonium (NH4).
• They are critical in the biosphere's nitrogen cycle.
• Some chemosynthetic bacteria symbiotically live with animals near volcanic activity on the sea floor.
• Discovered in the 1970s, this type of energy is not dependent on solar energy.

Photoautotrophs

• Photoautotrophs use energy from sunlight through photosynthesis.
• Light can be defined as a wave or a particle (photon).
• Infrared (IR) light has long wavelengths and low energy, interacting with matter to increase motion.
• Ultraviolet (UV) light has short wavelengths and high energy, which can destroy biological structures.
• Photosynthetically Active Radiation (PAR) falls between IR and UV and is used for photosynthesis.
• PAR is quantified as photon flux density, measuring the number of photons striking a square meter each second.
• Chlorophyll absorbs light as photons.

Photosynthesis

• Light reactions use light energy and occur in chloroplast thylakoid membranes, producing ATP, NADPH, and O2.
• The Calvin cycle takes place in the chloroplast stroma and uses ATP and NADPH to synthesize carbohydrates from CO2.

C3 Photosynthesis

• C3 photosynthesis is common in most plants and algae, where CO2 combines with ribulose bisphosphate (5-carbon sugar).
• This splits into two molecules of phosphoglyceric acid (PGA), a 3-carbon acid, giving C3 its name.
• The process requires plants to open stomata to fix carbon, which leads to water loss.

Photorespiration

• Photorespiration occurs when the Calvin cycle runs backwards, with Rubisco acting as an oxygenase, adding O2 to RuBP and releasing CO2.
• This process is wasteful and more likely in hot, dry environments when CO2 levels are low and O2 levels are high.

C4 Photosynthesis

• C4 photosynthesis minimizes photorespiration by reducing internal CO2 levels, increasing CO2 diffusion, and needing fewer open stomata, thus conserving water.
• C4 acids produced during carbon fixation move to specialized bundle sheath cells and this helps with gaining C02 in hot dry environments.
• C4 plants are found in low latitudes with warm and sunny areas.

CAM Photosynthesis

• CAM (Crassulacean Acid Metabolism) is mainly used by succulent plants in arid environments, where carbon fixation happens at night to reduce water loss.
• CAM photosynthesis has low rates and is extremely water use efficient.
• CAM plants grow very slowly.

Water Use Efficiency

• C3 plants lose 380 to 900 g H2O per g tissue.
• C4 plants lose 250 to 350 g H2O per g tissue.
• CAM plants lose about 50 g H2O per g tissue.
• C3 plants are less efficient in fixing CO2 than C4 plants, but do better in cool, wet environments with low solar radiation.

Plant Defenses Against Herbivores

• Plants use physical defenses like thorns and silica.
• Plants employ chemical defenses such as cellulose, lignin (high C:N ratio), toxins, and digestion-reducing compounds.
• Herbivore pressure is higher in the tropics.

Detritivores

• Detritivores consume food with high carbon and energy, but low nitrogen.

Adaptations

• Insects use camouflage to resemble twigs, leaves, or bird droppings.
• Müllerian mimicry involves noxious species converging in appearance.
• Batesian mimicry involves palatable species copying unpalatable ones.
• Armor and weaponry include turtle shells, beetle exoskeletons, horns, and antlers.

Symbioses

• Symbioses occur between autotrophs and heterotrophs, such as plants and myco fungi.

Biomass Composition

• Five elements (CHO, N, P) make up 93-97% of the biomass of plants, animals, fungi, bacteria, and protozoa.
• The remaining 3-7% includes elements like K, Ca, Mg, S, Cl, Fe, Mn, B, Zn, Cu, Mo, Na*, and I*.

Stoichiometry

• Stoichiometry deals with the conservation of matter in chemical reactions and helps define trophic interactions.

Carbon to Nitrogen Ratio

• Plants have a C:N ratio of about 25:1.
• Animals have a C:N ratio of about 5:1.
• Bacteria have a C:N ratio of about 5:1.
• Fungi have a C:N ratio of about 10:1.
• Herbivores need to eat a lot of plant matter to get enough nitrogen, because plant tissue has more carbon than nitrogen.

Optimal Foraging Theory

• Optimal foraging theory predicts organisms feed to maximize or minimize quantities like energy intake or predation risk.
• Energy supplies are limited, and organisms cannot maximize all functions at once due to the principle of allocation.
• Natural selection supports individuals who acquire energy efficiently (optimization), and experiments show both animals and plants forage optimally.

Behavioral Ecology and Sociobiology

• Behavioral ecology is the study of interactions between organisms and the environment mediated by behavior.
• Sociobiology studies social relations.

Fitness

• Fitness equals the number of offspring contributed by an individual relative to the number of offspring produced by others in the population.

Reproductive Strategies

• Asexual reproduction occurs without gamete formation, like budding, fission, parthenogenesis, spore formation, and vegetative propagation.
• Hermaphroditic organisms have both male and female reproductive organs.
• Separation of sexes involves having males and females as different individuals, leading to mate choice and sexual selection.

Natural Selection

• Selection for attributes (physical or behavioral) that contribute to fitness.

Sexual Selection

• Selection for attributes (physical or behavioral) that contribute to a reproductive advantage. Intrasexual Selection
• Intrasexual selection involves individuals of one sex competing among themselves for mates. Intersexual Selection
• Intersexual selection involves one sex consistently choosing mates based on a particular trait in the opposite sex.
• Runaway sexual selection suggests extreme male traits can evolve as the male trait and female preference become genetically linked.
• The male trait only needs to attract females and increase reproductive success.

Sociality Evolution

• Evolution of sociality (group living) is generally accompanied by cooperative feeding, defense, and restricted reproductive opportunities.
• Cooperation involves resource exchanges or other forms of assistance.
• Eusociality features multiple generations living together, cooperative care of young, and division into reproductive and non-reproductive roles.
• Naked mole rats are eusocial mammals.

Group Living

• Group living benefits include increased access to food and protection from predators.
• Costs include that only a few reproduce in a group and help raise offspring, and the increased fitness of mating individuals occurs at the expense of helpers.
• This is offset through inclusive fitness and kin selection, where individuals increase their inclusive fitness by supporting relatives, explaining how cooperation evolves.