Food Webs

A food web consists of many intertwined food chains. This web demonstrates multiple predator-prey relationships. The food chains that are represented are as follows:

  • Berries --> Blister Beetle --> Quail --> Snake
  • Berries --> Blister Beetle --> Quail --> Mountain Lion
  • Berries --> Quail --> Coyote
  • Berries --> Mule Deer --> Fennec Fox --> Mountain Lion
  • Berries --> Mule Deer --> Mountain Lion
Of the organisms present only the Berries are primary producers. The Blister Beetle and the Mule Deer are herbivores (plant eaters). The Quail is an omnivore (eats both plants and animals) due to the fact that it eats both the Berries and the Blister Beetle. The Fennec Fox, Coyote, and Mountain Lion are all carnivores (meat eaters) because they eat other organisms. The Fennec Fox is also a scavenger, preying off of other carnivores' kills when they can, but when necessary they will eat berries.
Decomposers are also an essential part of food webs, they break down all matter into simpler substances. They are typically forms of fungi and bacteria, but in a desert it is difficult for these types of decomposers to survive in the desert biome. So instead, the more common decomposers in this region consist of beetles, earthworms, and millipedes.

Food Chains 

In this example of a desert food chain, the members of this food chain are the cactus fruit (producer), the jack rabbit (herbivore), and a kit fox (carnivore). In this drawing, the energy flows from right to left. The rabbit eats the fruit of the cactus and the fox eats the rabbit. in a food chain, it represents a series of organisms interrelated in their feeding habits, the smallest being fed upon by a larger one, which in turn feeds a still larger one. 

In food chains, the first organism listed is the primary producer. The second organism is the primary consumer, the third is the secondary consumer, and the fourth organism is the tertiary consumer. 

In a food chain, energy is transferred and lost as it advances from organism to organism. With producers 100% of the energy is present, but when it is transferred to the primary consumer, 90% of the energy is lost. Where does this energy go? Some of the energy is used by the producer, and a majority of the energy is lost though waste and heat.

Abiotic Factors present in this food chain and how it effects the organisms:

  • Very Little Rainfall - limits the types of organisms that are present and can successfully reproduce and survive
  • Soil that is rich in minerals - little rain means that minerals are not carried deep into the soil
  • Occasional High winds - little to no topsoil
  • Temperature - differences from night to day are drastic

Predator-Prey Relationship 

Predators and prey are dependent upon one another to maintain population sizes. An example of a Predator-Prey relationship is a Mule Deer and a Mountain Lion.

Predator-Prey relationships are interconnected and completely dependent upon one another. As large numbers of that predator dies out due to natural/outside influences, the population of the prey will increase.

As the population of prey increases, it becomes easier to hunt them and the predators are able to obtain plenty of food and can reproduce, restoring the population. The prey is eaten at alarming rates and are killed by all of the prey that is eating them. 

The predator dies have a very small remaining food source and many of the predators are able to get enough food to survive, resulting in their death.

The relationship continues in a similar fluctuating pattern and does not stop until either the prey or the predator are removed from the environment.

Limiting Factors

There are two different types of limiting factors that exist within an ecosystem. The first type of limiting factor is density-dependent. Density-dependent is related to the size of a population and will occur if the population grows too large. Examples of density-dependent limiting factors include:
  • Parasitism
  • Availability of Food
  • Predation
  • Disease
  • Migration
The other limiting factor is density-independent and, as the name suggests, is not controlled by the size of a population. Examples of density-independent limiting factors include:
  • Natural Disasters (Earthquakes,  Droughts)
  • Weather Conditions (Temperature, Sunlight, etc.)
  • Water Flow Through a Region
  • Soil Quality

Invasive Species

Invasive Species are species that are brought from their original regions and are put in another region. They typically thrive due to the absence of natural predators and diseases. Because of this, they generally run rampant and can be harmful to the natural species that live there.

An example of an invasive specie in the desert is the Red Imported Fire Ant (RIFA). RIFA are originaly from South America and was brought accidentally  to North America in ships' ballasts in the 1930's. RIFA are small but extremely aggressive. RIFA's sting repeatedly and inject highly toxic venom is ejected with each sting. If a human is stung, the toxins make the surrounding area burn and itch for an hour, soon there after, the burning changes into a large, white blister that if it is popped can lead to a second degree infection.

What effect does this have on the animals of the desert biome?

They generally out compete and eliminate other types of native fire ants. RIFA attack eggs and young of many bird and reptilian species. In areas where there is a high concentration of RIFA, the population of northern bobwhite quail has decreased significantly and may completely annihilate ground-nesting species from a certain area. They can also attack small mammals such as rodents and have been known to kill newborn deer and cattle. 

 Energy Pyramid

 An energy pyramid, as shown to the right, shows the transfer of energy between organisms. Each level is called a Tropic Level.  The autotrophs (producers) make up the bottom tropic level of the the pyramid. These autotrophs currently possess 100% of the available energy since getting it directly from the sun. In this diagram, the autotroph comes in the form of a Sprawling Prickly Pear.

The first heterotroph (primary consumer) is in the middle section of the pyramid. Although the energy level that this tropic level possess is approximately 10%. This heterotroph is a Sand Grouse. The third tropic level is also a heterotroph (secondary consumer). The energy level has decreased to only 1%. A Fennec Fox is the secondary consumer in this particular energy pyramid.

What causes the energy to be lost? Energy is lost because it is used by the organisms, but most of the energy disappears through the loss of heat and waste products.