Ecology Sept. 11th (new .2)
Environmental Conditions and Tolerance
Organisms must tolerate environmental conditions, specifically temperature and water quality, to persist in ecological systems.
Temperature impacts: Affects enzyme activity, metabolic rates, and biochemical processes critical for survival.
Water quality impacts: Influences solute concentrations, pH, and the availability of dissolved oxygen, all vital for physiological functions.
Autotrophs and Energy Acquisition
Definition of Autotrophs: Organisms that produce their own energy, primarily through photosynthesis or chemosynthesis.
Photosynthesis:
Most recognized form of energy acquisition.
Utilizes sunlight to convert CO₂ and water into organic compounds (sugars) and oxygen: \text{6CO}2 + \text{6H}2\text{O} + \text{Light Energy} \rightarrow \text{C}6\text{H}{12}\text{O}6 + \text{6O}2 (where C6H{12}O_6 represents glucose).
Chemosynthesis:
Energy derived from the oxidation of inorganic compounds like hydrogen sulfide (\text{H}2\text{S}), ammonia (\text{NH}3), or ferrous iron (\text{Fe}^{2+}).
This energy is converted into chemical energy stored in organic molecules.
Key transformation of energy from one form to another, often observed in extreme environments like hydrothermal vents.
Synonymous Relationship: Carbon is often equated with energy due to carbon bonds releasing CO₂ during respiration.
Autotrophs are essential as they serve as the primary producers of energy in ecosystems.
Heterotrophs and Energy Utilization
Definition of Heterotrophs: Organisms that acquire energy by consuming organic compounds from autotrophs or other heterotrophs.
Heterotrophs have diverse feeding strategies:
Detritivores: Consume dead organic matter (e.g., leaf litter, decaying animals), playing a crucial role in nutrient recycling.
Parasitic Organisms: Feed on living hosts without necessarily killing them (e.g., tapeworms, ticks), obtaining nutrients directly from host tissues.
Predators: Capture and consume live prey (e.g., lions, eagles), often involving complex hunting strategies.
The nutrition strategies of heterotrophs influence their physiological adaptations and success in different environments.
Unique Autotrophic Exceptions
Parasitic Plants: Holloparasites:
Lack photosynthetic pigments and rely entirely on other plants for nutrients.
Example: Dodder (Cuscuta spp.), which wraps around host plants and extracts nutrients via specialized structures called haustoria.
Visual illustration of biomass changes between host and parasite.
Hemiparasites: Partially autotrophic and heterotrophic.
Example: Mistletoe obtains water and nutrients from host plants while also photosynthesizing with its own chlorophyll.
Photosynthetic Animals:
Certain sea slugs (e.g., Elysia chlorotica) can steal chloroplasts from algae (kleptoplasty), incorporating them into their own cells and performing photosynthesis without their own mechanisms.
Key Photosynthetic Mechanisms and Constraints
Light Harvesting:
Organisms utilize pigments such as chlorophyll to capture light.
Chlorophyll absorbs blue and red light and reflects green, giving plants their characteristic color.
Different types of chlorophyll (e.g., chlorophyll a and b) allow adaptation to specific light availabilities (shade vs. full sunlight).
Process of Photosynthesis:
Light Reactions: Occur in the thylakoid membranes of chloroplasts; convert solar energy to chemical energy (ATP and NADPH), using electrons from water molecules, releasing oxygen as a byproduct.
Dark Reactions (Calvin Cycle): Occur in the stroma of chloroplasts; utilize ATP and NADPH from the light reactions and CO₂ to form glucose precursors (glyceraldehyde-3-phosphate, G3P), which are then used to synthesize carbohydrates.
Factors Affecting Photosynthesis:
Temperature and water availability directly influence photosynthetic rates and overall productivity of ecosystems, as they impact enzyme activity and stomatal opening.
Light Compensation and Saturation Points
Light Compensation Point: The light intensity at which the rate of photosynthesis exactly balances the rate of respiration. Plants lose energy in darkness but begin gaining it once reaching this threshold.
Light Saturation Point: The maximum photosynthesis rate is achieved, constrained by the carbon fixation capacity set by dark reactions, even if light intensity continues to increase.
Physiological Adaptations to Light Environments
Plasticity in Leaves: Adaptations based on exposure to varying light levels.
Sun Leaves vs. Shade Leaves: Sun leaves are typically smaller and thicker with more palisade cells and stomata to maximize light absorption and CO₂ uptake; shade leaves are larger and thinner to minimize material waste and capture diffuse light effectively.
Temperature and Photosynthetic Efficiency
Plants exhibit different photosynthetic rates at varying temperatures, with an optimal temperature range for maximum efficiency.
Adjustments in physiology occur based on prior growth conditions (e.g., seasonal changes), showing acclimation to prevailing thermal environments.
Nitrogen and Other Nutrient Availability
Nutrient availability, especially nitrogen, significantly impacts photosynthesis due to its role in protein synthesis (e.g., components of chlorophyll and Rubisco).
High nitrogen content generally increases photosynthetic rates but can also attract herbivores due to increased palatability of nutrient-rich tissues.
Enzymatic Activity and Efficiency
Ribulose bisphosphate carboxylase/oxygenase (Rubisco):
A crucial enzyme that acts as both a carboxylase (fixing CO₂) and an oxygenase (fixing O₂); impacts efficiency under various conditions of CO₂ and O₂ levels.
Photorespiration: When Rubisco acts as an oxygenase, it combines O₂ with RuBP instead of CO₂, releasing CO₂ and consuming ATP. This process reduces photosynthetic efficiency, especially under high temperatures and low CO₂/high O₂ conditions.
Changes in enzyme activity due to temperature and photorespiration can decrease photosynthetic efficiency.
Adaptive Strategies in Response to Environmental Pressures
Under low CO₂ and high temperature conditions, plants evolved C4 and CAM pathways for greater efficiency to overcome photorespiration.
C4 Photosynthesis:
Different carbon fixation methods unique to plants like corn and sugarcane.
Uses the enzyme PEPcase to efficiently capture CO₂ in mesophyll cells, forming a 4-carbon compound, which is then transported to bundle-sheath cells (Kranz anatomy) where CO₂ is released and concentrated for the Calvin cycle, thereby minimizing photorespiration losses.
CAM Photosynthesis:
Crassulacean Acid Metabolism (CAM) involves a temporal separation of CO₂ fixation and the Calvin cycle adaptation.
Stomata open at night to fix CO₂ into organic acids (stored in vacuoles) when temperatures are cooler and humidity is higher, minimizing water loss.
During the day, stomata close, and the stored CO₂ is released for the Calvin cycle, critical for desert plants like cacti and succulents.
Heterotrophic Feeding and Digestion Processes
Energy acquisition strategies in heterotrophs depend on the energy density of their food sources and the effort expended to obtain it.
Different Food Types:
Fats provide the highest energy per mass ( \approx 9 \text{ kcal/g} ), followed by carbohydrates ( \approx 4 \text{ kcal/g} ), proteins ( \approx 4 \text{ kcal/g} ), and then fiber, which is mostly indigestible by many organisms.
Secondary compounds from plants (e.g., tannins, alkaloids) may hinder digestion and impair energy intake by acting as toxins or reducing nutrient absorption.
Evolution of Feeding Strategies in Heterotrophs
Variants in mouthpart structures among animals (e.g., beaks, teeth, proboscises) allow access to food sources inaccessible to other species, demonstrating adaptability to gain energy efficiently.
Examples include specialized feeding adaptations seen in birds (e.g., hummingbirds with long beaks for nectar), insects (e.g., butterflies with siphoning mouthparts), and mammalian predators (e.g., sharp canines for tearing meat).
Digestion in Relation to Food Type
Length and complexity of the digestive systems correlate with the dietary habits of animals, influencing how effectively they extract energy from food.
Herbivores, with diets rich in cellulose, often have longer and more complex digestive tracts with specialized fermentation chambers (e.g., ruminants) compared to carnivores.
Birds in migration exhibit digestive system adaptations based on fat versus carbohydrate-rich diets, sometimes shortening their intestines to reduce weight when consuming high-energy fat, and lengthening them for carbohydrate-rich diets.
Intelligence and Tool Use in Energy Acquisition
Human efficiency in energy extraction is amplified through technology; comparison to animal tool use highlights unique adaptations in cognition and learning behaviors in crows and dolphins.
Tool-Making Behavior: Observations of learned behaviors in tool use among crows (e.g., crafting hooks from leaves to extract insects) and other animals (e.g., sea otters using rocks to crack shells) emphasize the evolutionary advantages of specialized techniques in energy acquisition.
Conclusion
The study of autotrophs and heterotrophs reveals intricate interdependencies within ecosystems, with specific adaptations evolving in response to environmental pressures. Understanding these dynamics is critical in addressing ecological and conservation questions going forward.