Resource Availability in Ecosystems

Ecological Impact of Wildfires on Forest Resources

Wildfires represent a significant environmental factor that can be initiated by human activity or natural events, such as a lightning strike. When observing the aftermath of a wildfire in a green forest, the immediate physical changes are stark, typically involving a charred landscape where many organisms have been killed. While some mobile organisms, such as birds or larger mammals, may be able to run or fly away to avoid direct harm from the flames, they nonetheless suffer from the loss of critical resources including nests, dens, and other forms of shelter. Consequently, an area affected by a major wildfire is unlikely to support the same community of organisms immediately following the event as it did prior to the fire.

Fundamental Principles of Biological Growth and Resource Necessity

All living organisms must obtain specific resources from their environment to sustain life and facilitate growth. These essential resources include food, water, and shelter. Within an ecosystem, these resources are categorized as either living (biotic) or nonliving (abiotic). The overall health and development of both individual organisms and entire populations are strictly dependent on the availability of these resources within their specific ecosystem. Without sufficient resources, an individual cannot survive, grow to maturity, or eventually reproduce.

Individual growth is exemplified by the transition of a hatchling from a tiny egg into a large sea turtle, or an acorn developing into a towering tree. These processes require a consistent intake of resources. At the population level, the growth of a group of organisms also depends on resource abundance. If the organisms in an ecosystem have an abundance of needed resources, the number of individuals in a population will likely increase, leading to population growth.

Factors Influencing Resource Availability

Several factors can influence how resources are distributed and available within an ecosystem. An increase in population size directly leads to a higher demand for resources, which may result in fewer resources being available for each individual. Furthermore, different populations of organisms often share the same resources, such as water or food sources. This overlap leads to competition between different populations or between individuals within the same population. Such competition frequently results in limited resource availability for some members of the ecosystem.

Environmental factors also play a critical role. For instance, following a rainy season, plants may produce a high volume of seeds. This temporary abundance of food can allow a deer population to expand. However, if the rain stops and plant productivity decreases, the deer population will subsequently decline. Natural events, including floods, droughts, and wildfires, can suddenly and temporarily reduce resource availability, causing immediate population decreases. For example, a drought could dry up a river, leaving both fish and birds without the water and food resources necessary for survival.

Classification of Biotic and Abiotic Resources

Abiotic factors are the nonliving components of an ecosystem that are essential for survival. These include air, water, nutrients, soil, sunlight, and rainfall. A specific example is the amount of oxygen dissolved in lake water, which is a critical abiotic resource for fish. When dissolved oxygen is plentiful, fish populations tend to be healthy and grow in size. If oxygen levels become limited, the health of individual fish suffers, leading to a population decline. In a rainforest environment, sunlight often becomes a limiting factor at the bottom of the canopy, whereas shelter and water may be limited at the top of the canopy levels.

Biotic factors are the living parts of an ecosystem or those related to the activity of living things, such as bacteria, algae, fungi, plants, animals, and decaying organisms. Biotic resources are highly interconnected; for example, if a fungus destroys the fruits of a tree that a specific insect species relies on for food, that insect population will decrease. This reduction then impacts other animals that feed on the insect, potentially causing a cascade of resource scarcity that reaches the top of the food chain. Limits to any single biotic factor can effectively impact all other factors within the ecosystem.

Dynamics of Resource Abundance and Exponential Growth

When resources in an environment are abundant, a population may grow at an increasing rate known as exponential growth. This occurs when the population size increases by a repeated factor over time. A study of a deer population over a $60$-year period demonstrated this phenomenon. In this specific study, the largest deer population reached approximately $1,300$ individuals about $40$ years into the study. The population experienced a phase of exponential growth from approximately year $14$ to year $40$. This growth was likely driven by an abundance of food plants and a potential decrease in predator populations. However, such periods are often followed by a population crash or a large decrease when the resources can no longer support the expanded population size or when predators increase.

Resource abundance can be natural or human-induced. A natural example involves periodical cicadas, which have $13$-year or $17$-year life cycles. When these cicadas emerge in massive numbers, they provide an incredible abundance of food for their predators. A human-induced example is an algal bloom. This occurs when rainwater runoff carries garden and agricultural fertilizers, which are rich in nutrients, into aquatic ecosystems. The sudden abundance of nutrients causes extreme growth in algal populations. If these algae do not run out of nutrients, their growth may eventually be limited by other factors such as physical space to grow or the availability of dissolved oxygen in the water.

Human Impact and Conservation Labors

Human activities significantly alter resource availability through habitat destruction and forest fragmentation. Dividing large, continuous forests into smaller parts can prevent certain bird species from finding nesting sites. In such cases, birds are often forced to move to other areas to find shelter resources rather than waiting for a site to become available or building different types of shelter. This movement is necessary to ensure the continuation of the population.

Conservation efforts have historically addressed these issues. President Theodore Roosevelt, who served from $1901$ to $1909$, was a major proponent of the national park system, creating five national parks, $51$ bird sanctuaries, and over $100$ million acres of national forest to protect wildlife from human development. Modern strategies to mitigate human impact include promoting sustainable practices, using renewable energy, recycling, and efficient water management. In regions like the UAE, significant ecological problems include deforestation, water shortages, soil degradation, loss of biodiversity, and pollution.

Questions & Discussion

Question: Imagine that you saw a huge green forest one day, and the next day you saw a scene of wildfire destruction. Describe what you observe and how living things were affected. Answer: Observations should include the charred remains of trees and a lack of green foliage. The fire likely killed many organisms. While some may have escaped, they lost their nests and dens. The area will likely not support the same community it did before the fire.

Question: What resources do the egret and stork compete for in the Alligator Rivers region of Australia? Answer: They share and compete for resources including water, nesting materials, and fish to eat. Factors such as drought could dry up the river and leave both populations without fish or water.

Question: Differentiate between abundant and scarce resources and how they relate to population size. Answer: Abundant resources support growth by providing enough food, water, and space. Scarce resources lead to competition, starvation, and decline. The relationship is direct: when resources are plentiful, populations grow; when they are scarce, populations decline due to higher mortality and lower reproduction.

Question: Which factor directly reduces resource availability when population size increases? Answer: Higher demand for resources.

Question: What happens when different populations compete for the same resources? Answer: Resources become limited.

Question: Which natural event can suddenly reduce resource availability? Answer: Floods or droughts.

Question: How does an increase in the hyena population affect the population of lions in African ecosystems? Answer: Lions and hyenas rely on the same food resources. An increase in the hyena population would limit the food available for lions, increasing competition between the two groups.

Question: How might an abundance of food resources affect a caribou population? Answer: The population would increase in size and there would be less competition between the caribou for food.

Question: How would a shortage of water likely affect the caribou? Answer: The population would decrease in size and the growth of individual caribou would decrease.