Ecological Relationships in Human and Social Biology

Introduction to Ecological Relationships

Ecological relationships describe the interactions between organisms and their environment, as well as the interactions among organisms within an ecosystem. These relationships determine the flow of energy and nutrients through biological communities.

Components of an Ecosystem

Biotic Abiotic Interactions Ecosystem

Figure 1: Components of an ecosystem showing biotic and abiotic factors

Types of Ecological Relationships

1. Predator-Prey Relationships

One organism (predator) hunts and consumes another (prey):

Predator (Lion) Prey (Zebra)

Figure 2: Predator-prey relationship

2. Symbiotic Relationships

Close, long-term interactions between different species:

Type Description Example
Mutualism Both species benefit Bees and flowers
Commensalism One benefits, other unaffected Barnacles on whales
Parasitism One benefits, other is harmed Tapeworm in human gut
Mutualism Commensalism Parasitism

Figure 3: Types of symbiotic relationships

3. Competition

Organisms vie for the same limited resources:

Tall Tree Medium Tree Small Tree Sunlight Competition

Figure 4: Competition for sunlight among trees

Energy Flow in Ecosystems

Energy moves through ecosystems in food chains and webs:

Food Chain Example

Grass Grasshopper Frog Snake Hawk

Figure 5: Simple food chain showing energy transfer

Ecological Pyramid

Producers (Plants) Primary Consumers Secondary Consumers Tertiary Consumers 100% Energy 10% Energy 1% Energy 0.1% Energy

Figure 6: Energy pyramid showing 10% energy transfer between trophic levels

Human Impact on Ecological Relationships

Glossary of Terms

Ecosystem
Community of interacting organisms and their physical environment.
Biotic Factors
Living components of an ecosystem (plants, animals, microbes).
Abiotic Factors
Non-living components (temperature, water, sunlight, soil).
Trophic Level
Position an organism occupies in a food chain.
Food Web
Complex network of interconnected food chains.
Niche
An organism's role in its ecosystem including habitat and relationships.
Biomass
Total mass of living organisms in a given area.
Carrying Capacity
Maximum population size an environment can sustain.

Self-Assessment Questions

1. Define the term 'symbiosis' and give one example.
Symbiosis is a close, long-term interaction between different biological species. Example: Lichen (fungus + algae), where the fungus provides structure and the algae provides food through photosynthesis.
2. What is the difference between interspecific and intraspecific competition?
Interspecific competition occurs between different species (e.g., lions and hyenas competing for prey), while intraspecific competition occurs within the same species (e.g., two male deer competing for mates).
3. Explain why there are typically fewer organisms at higher trophic levels.
Energy is lost at each trophic level (about 90% as heat/metabolism), so less energy is available to support organisms at higher levels. This results in fewer organisms that can be supported at each successive level.
4. Describe one mutualistic relationship and how each organism benefits.
Example: Bees and flowering plants. Bees benefit by getting nectar (food), while plants benefit through pollination which allows them to reproduce. Both species gain an advantage from the relationship.
5. How might deforestation disrupt ecological relationships in a forest ecosystem?
Deforestation destroys habitats, removes food sources, disrupts predator-prey relationships, eliminates symbiotic partnerships, reduces biodiversity, and alters abiotic factors like soil quality and water cycles.
6. What is the role of decomposers in ecological relationships?
Decomposers (like fungi and bacteria) break down dead organisms, returning nutrients to the soil which are then available for producers. They complete nutrient cycles and prevent accumulation of dead matter.
7. Explain how predator-prey relationships can lead to population cycles.
As prey population increases, predators have more food and their population grows. Increased predation then reduces prey population, leading to predator starvation and decline. With fewer predators, prey population recovers, repeating the cycle.
8. Why are parasites not considered predators?
Parasites typically don't kill their hosts (at least not immediately), living on or in them long-term. Predators kill and consume prey quickly. Parasites are usually much smaller than their hosts, while predators are often larger than prey.
9. Describe how energy flows through a food web differently than nutrients.
Energy flows one-way through ecosystems (sun → producers → consumers → heat loss), while nutrients cycle continuously (decomposers return nutrients to soil for reuse by producers).
10. How might climate change affect ecological relationships in the Arctic?
Melting ice reduces polar bear habitat (predator-prey imbalance), warmer temperatures allow invasive species to compete with natives, changing seasons disrupt migration patterns, and altered temperatures affect plant growth cycles that animals depend on.

Summary of Key Points