miércoles, 7 de julio de 2010


JULY 7TH /2010
Desert Food Chains
Food chains allow us to examine the basics of how energy passes through an ecosystem.
A food chain is sequence of plants, herbivores and carnivores, through which energy and materials move within an ecosystem. Food chains are usually short and not more than three or four links. They usually consist of a producer, a consumer and a predator, with the predator being the top of the food chain. The top of the desert food chain does eventually die though, and is returned to the bottom of the chain as nutrients by decomposers. Typical Desert Food Chains
Mountain LionMule DeerPlant (forbs)
CoyoteQuailPlant (shrub seeds)
SnakesLizardsInsectsPlant (wildflower/grass seeds)
HawkSnakesRatsPlant (seeds)
Desert Food PyramidA pyramid representing trends in food consumption, with the lowest level (primary producers) having the greatest total biomass, and the higher consumer levels having successively less total biomass. The concept of a pyramid of consumers in an ecosystem helps to understand how an organism fits into a community as a whole. Typical Desert Food Pyramid
4th Trophic Level:Tertiary ConsumersCarnivoresThese are high level consumers, carnivores that will eat other carnivores.3rd Trophic Level:Secondary ConsumersSmall CarnivoresThe predators are the secondary consumers. They occupy the third trophic level. Again we see cold-blooded animals, such as snakes, insect-eating lizards, and tarantualas. Only about 2 Kilocalories per square meter per year are stored in their bodies. In the harsher desert environments, they are the top predators. 2nd Trophic Level:Primary ConsumersHerbivoresThese animals are usually small and eat little. Many are insects, or reptiles, who are cold blooded and who use less energy to maintain their bodies than mammals and birds do. As food for predators, they provide about 20 Kilocalories per square meter per year for predators.Including:Ants and other insects, rats and mice, some reptiles the largest of which are the tortoise and chuckwalla. 1st Trophic Level:Primary ProducersPlantsThese are plants that make food through photosynthesis. Limited by the availability of water, they produce fewer than 200 Kilocalories of food for the animals for each square meter each year.Including:Trees, shrubs, cactus, wildflowers, grasses
Primary ProducersFood chains are divided into nutritional or trophic levels. The first trophic, or lowest level, is occupied by the primary producers, plants.Plants produce energy from photosynthesis. Plants produce energy to use for survival, growth and to store when production resources are not available. The amount of energy produced is measured in kilocalories and limited by the availability of sunlight, water and nutritional resources available to the plant. In the desert biome water is the determining resource. In an environment where water is readily available (such as an oasis, spring or desert riparian biomes) more plant diversity is available and more kilocalories of energy are produced. In a sparse, dry ecosystem, where plants can not survive unless widely spaced, only about 200 kilocalories of food per square meter per year are produced.Primary ConsumersPrimary consumers are the animals that eat the plants. These animals, including insects, occupy the second trophic level. Energy is tranferred from the plants to the consumers as food for the consumers. Although primary consumers are for the most part herbivorious, this is where the line between the primary and secondary consumers begins to blur. In a mammal, such as the desert pocket mouse, food is consumed and converted to energy. The mouse, being warm-blooded, uses this energy in several ways.
1. The mouse recieves stored energy by eating food.2. The mouse's metabolism converts stored energy from the food to available energy for it's survival. To survive the mouse needs to grow, acquire more food, escape predators, etc). Some energy is lost to heat, but this heat can be helpful to keep the mouse's body at a normal temperature in cold weather.3. Some energy is lost in the production and passing of waste as unprocessed nutrients.4. About 90% of the energy the mouse converts from food is stored and used by the mouse. The remaining 10% is available for consumption by predators at the next trophic level.
Secondary Consumers - Small PredatorsTertiary Consumers - Large Predators

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