Ecosystem Dynamics: Food Webs and Nutrient Cycles
Ecosystem Concepts
Food Web: Species Nutritional Relationships
Food Web: Relation of nutrition among several species. (Example): Algae → Larvae → Nase → Kingfisher.
Food Web: This comprises a group of interconnected feeding strings.
Trophic Levels
Trophic Level: Producer → Primary Consumer (C. primarios) → Secondary Consumer (C. secundarios) → Tertiary Consumer (C. terciario) → Superpredator.
Matter Cycling and Energy Flow
Cycle of Matter: Inorganic matter becomes organic (Example): Bacteria → Fungi.
Flow of Energy: The energy of the sun is captured by photosynthetic organisms, which absorb energy and transform it into chemical energy. This energy is fixed. When energy can no longer be retrieved and incorporated back into the flow, we speak of energy loss in ecosystems.
Essential Nutrients
- Micronutrients: Calcium, magnesium, sulfur, iron.
- Macronutrients: Water, carbon dioxide, oxygen, nitrogen, phosphorus, potassium.
Plant Water Dynamics and Digestion
Water Movement Triggers in Plants
Root Pressure: The water pressure in the root that causes osmosis, moving water out through the root.
Transpiration: When water evaporates from the cells of leaves, the solutes in the cells become concentrated. Water moves to adjacent cells, a process repeated until it reaches the xylem.
Digestion Mechanisms
Intercellular Digestion: This is more complex and specialized in capturing food than intracellular digestion.
Digestion in Coelomate Animals
Coelomate animals possess a digestive cavity that is an open tube to the exterior with two openings: the mouth, for food entry, and the anus, for waste egestion or excretion of unabsorbed material. Specialized glands exist for secreting substances that facilitate digestion.
Digestive Systems in Invertebrates
- Digestion in Annelids: The alimentary canal is elongated.
- Digestion in Molluscs: They possess a radula in the mouth for scraping food. The voluminous viscera contain the "hepatopancreas."
- Digestion in Arthropods: Digestion occurs in the stomach; they have specialized mouthparts and intestinal absorption.
- Arachnids: They secrete digestive enzymes onto the prey; digestion is partially external.
- Echinoderms (D.): They have the ability to evert (draw out) their stomach to engulf carnivorous prey.
Dietary Classifications and Cellulose Digestion
Carnivores and Omnivores: They do not digest cellulose due to the small size of the cecum and colon.
Herbivores:
- Non-ruminants: They utilize only part of the ingested cellulose because the residence time of the food bolus in them is relatively short.
- Ruminants: The rumen specializes in hosting the bacteria that degrade cellulose.
Stages of Digestion
- Ingestion: The entry of food into the mouth.
- Mastication (Grinding): This is performed by chewing with the teeth and through the movements of the stomach.
- Transport: Occurs through peristalsis, which involves muscular contractions of the tube walls.
- Chemical Digestion: Through digestive juices secreted by attached glands.