Ecosystem Dynamics and Social System Comparisons

1. “...there is constant interchange of … various kinds within each system, not only between the organisms but between the organic and inorganic. These ecosystems, as we may call them, are of ... various kinds and sizes.” — Tansley (1935)

Comparing Ecosystems and Social Systems

(a) Compare the characteristics of ecosystems and social systems. (5 points)

• Systems are assemblages of parts and the relationships between those parts, which together constitute the entity or whole.
• Both types of systems have common features such as inputs, outputs, flows, and stores.
• Social systems are more general; there are many different types, such as transport systems, economic systems, farming systems, or class systems.
• Energy and matter flow through ecosystems, whereas social systems have flows of information, ideas, and people.
• Both types of systems exist at different scales and share common features like feedback and equilibrium.
• Trophic levels in ecosystems correspond to levels in society.
• There are consumers and producers in both systems.

Species Interactions Within Ecosystems

(b) Describe how populations of individual species interact within an ecosystem, using named examples to support your answer. (6 points)

• Herbivory: When a consumer feeds on a producer. Example: A rabbit eating grass.
• Competition: A common demand by two or more organisms upon a limited supply of a resource (e.g., food, water, light, space, mates, or nesting sites). Example: Two male lions competing for the same territory and mates.
• Parasitism: A relationship between two species in which one species (the parasite) lives in or on another (the host), gaining all or much of its food from it. Example: Strangler fig tree and mahogany tree in a tropical rainforest.
• Mutualism: A relationship between individuals of two or more species in which both benefit and neither suffer. Example: Elephant and acacia tree.
• Predation: When one species hunts another. Example: Lion and wildebeest.

Climate and Net Primary Productivity

(c) Explain the relationship between climate and net primary productivity in two contrasting biomes you have studied. (7 points)

• Climate determines the global distribution and the productivity of biomes.
• Climate is a limiting factor as it controls the amount of photosynthesis that can occur in plants.
• Water availability, light, and temperature are the key climate controls.
• Photosynthesis is a chemical reaction; therefore, temperature affects rates of photosynthesis.
• Tropical Rainforests: These have high constant temperatures (typically 26 °C) and high rainfall (over 2,500 mm p.a.) throughout the year, resulting in high rates of NPP.
• Hot Deserts: These have high temperatures but low precipitation (typically under 250 mm p.a.); therefore, rates of NPP are very low.