FW - Diversity PDF

Aquatic Macrophytes Heterophylly: o Seen in species like Limnophila or Buttercup. Submerged leaves are finely divided for better gas exchange; aerial leaves are broader and undivided for better photosynthesis. o Regulated by light intensity and plan...

Aquatic Macrophytes Heterophylly: o Seen in species like Limnophila or Buttercup. Submerged leaves are finely divided for better gas exchange; aerial leaves are broader and undivided for better photosynthesis. o Regulated by light intensity and plant hormones like ethylene. Patterns of Plant Coverage: o Submerged → Floating-leaved → Emergent macrophytes. o Horizontal patchiness results from environmental variations like silt patterns or grazing by waterfowl. o Light availability affects depth distribution, but suspended particles or turbulence often reduce penetration more than expected. Primary Productivity: o Typically measured via changes in biomass or oxygen levels. Peaks in summer when sunlight is most available. Three Community Gradient: o Reservoirs: Emergent plants like cattails (Typha) dominate. o Natural Lakes: Floating species like water lilies (Nymphaea). o Rivers: Fast-flowing conditions favor emergent plants; submerged macrophytes are sparse. Algae Periphyton: o Includes organisms like diatoms and cyanobacteria, forming biofilms on submerged surfaces. o Produces substances that may inhibit their own growth or benefit aquatic invertebrates. Phytoplankton: o Diversity: Includes green algae (Chlorophyta), diatoms (Bacillariophyta), and cyanobacteria (Cyanophyta). o Sinking: Challenges countered by adaptations like: ▪ Low density: Gas vesicles (e.g., in cyanobacteria) reduce density. ▪ Shape adaptations: Spines (e.g., Asterionella) or flat forms slow sinking. ▪ Flagella: Seen in motile algae like Chlamydomonas. o Reproduction: Primarily asexual via cell division; some use sexual reproduction to survive harsh conditions.  Adaptations Against Predation: o Spines: Found in Ceratium to deter zooplankton grazing. o Mucous Sheets: Protect from digestion in herbivores’ guts. Taxonomy: o Based on cell wall composition and pigmentation (e.g., chlorophyll a, b). o Modern genomic techniques reveal greater diversity than classical taxonomy suggests. Distribution: o Dominance of certain groups correlates with productivity and pH (e.g., cyanobacteria thrive in nutrient-rich waters). Competitive Exclusion and the Paradox of the Plankton Core Idea: Traditional principles predict dominance by a few species due to resource competition. Yet, phytoplankton communities often support dozens of species. Hutchinson’s Proposal: o Environmental factors prevent equilibrium: ▪ Vertical gradients: Light and turbulence vary by depth. ▪ Differential predation: Herbivores target dominant species, allowing others to persist. ▪ Temporal variability: Seasonal changes in light and nutrients disrupt steady states. ▪ Symbiosis: Some algae form mutualistic relationships (e.g., with nitrogen-fixing bacteria). Key Themes 1. Diversity of Freshwater Invertebrates o Freshwater ecosystems host a wide range of invertebrates, from simple sponges to complex insects and crustaceans, each playing vital ecological roles. 2. Adaptations to Freshwater Environments o Unique morphological, behavioral, and reproductive adaptations enable species to survive and thrive in specific aquatic habitats. 3. Ecological Significance o Freshwater invertebrates contribute to nutrient cycling, energy flow, and food webs, supporting higher trophic levels. 4. Threats to Freshwater Biodiversity o Pollution, habitat destruction, climate change, and invasive species significantly threaten biodiversity.  5. Functional Roles and Species Interactions o Invertebrates act as detritivores, grazers, or predators. They engage in interactions like competition, predation, parasitism, and mutualism, which shape community dynamics. Species Overview Sponges (Phylum Porifera) Feeding: Filter feeders attaching to solid substrates like stones and macrophytes. Habitat: Found in clear water; highly sensitive to water quality. Symbiosis: Some sponges have mutualistic relationships with algae for survival in well-lit areas. Hydroids Structure: Simple body plan related to jellyfish and corals, with a central cavity. Feeding: Prey on small crustaceans, insect larvae, and worms. Reproduction: Asexual reproduction under optimal conditions. Mussels (Class Bivalvia) Structure: Two shells (valves) joined by an adductor muscle. Feeding: Filter feed on particulate organic matter. Lifecycle: Larvae (glochidia) parasitize fish gills for dispersal. Conservation: Freshwater unionid mussels are threatened by siltation, toxic compounds, and invasive zebra mussels. Rotifers Size: Tiny (0.1–1 mm); prolific reproducers. Features: o Corona: Ciliated region for feeding and locomotion. o Mastax: Muscular organ for grinding food. Reproduction: Parthenogenesis dominates; some species form colonies. Crustaceans (Phylum Arthropoda) General Characteristics Body: Segmented (head, thorax, abdomen) with an exoskeleton made of chitin and calcium carbonate. Respiration: Gills or direct diffusion. Reproduction: Sexual or asexual, with many producing resting eggs to survive adverse conditions. Crustacean Zooplankton Cladocerans ("Water Fleas"): o Examples: Daphnia, Bosmina, Chydorus. o Role: Graze on green algae and bacteria, controlling algal blooms. o Adaptations: Resting eggs (ephippia) ensure survival in harsh environments. Copepods: o Lifecycle: Multiple larval stages (naupliar, copepodite) before adulthood. o Feeding: Diet ranges from herbivory to predation. o Reproduction: Sexual, with resting eggs for unfavorable conditions. Other Crustaceans Mysids ("Opossum Shrimp"): Fast-swimming species in cold, oligotrophic lakes. Exhibit vertical migration and feed on phytoplankton. Isopods and Amphipods: Opportunistic foragers; isopods inhabit weed beds, while amphipods swim sideways. Decapod Crayfish: Largest and longest-lived freshwater crustaceans, generalist feeders, and economically significant in fisheries. Insects Secondary Colonists: Evolved from terrestrial ancestors. Respiration: Aquatic larvae or adults with air-breathing adaptations (e.g., "aqualunging"). Roles: Predators, herbivores, and detritivores within food webs. Other Vertebrates Include fish, amphibians, reptiles, birds, and mammals, contributing to freshwater biodiversity and ecosystem stability. General Patterns in Freshwater Diversity 1. Habitat Diversity and Stability: Greater habitat variety supports higher species richness. 2. Latitudinal Gradient: Species richness decreases with increasing latitude. 3. Size and Stability: Larger, more stable water bodies harbor more species. Seasonal Dynamics in Cold Temperate Lakes 1. Winter: Ice cover limits light; green flagellates dominate. 2. Spring: Ice melts, promoting diatom growth and algal biomass peaks. 3. Summer: Stratification leads to nutrient depletion and grazing by Daphnia. 4. Autumn: Storm mixing replenishes nutrients; diatom resurgence occurs. Case Study: Priest Pot Lake High Diversity: Hosts at least 800 species despite its small size. Cryptic Diversity: Includes undetected resting stages or unassessed groups like parasites. Technological Advances: Tools like environmental DNA (eDNA) enhance species detection. Threats and Conservation 1. Invasive Species: o Zebra mussels disrupt food webs and infrastructure. o Other invasive crustaceans outcompete native species. 2. Pollution: Eutrophication, sedimentation, and toxic runoff harm freshwater ecosystems. 3. Conservation Strategies: o Habitat restoration, pollution control, and coordinated land-water management.