Population Dynamics, Pesticides and Biodiversity Risks

Population in Ecosystems: Self-regulation

People in ecosystems — autoregulación: A population is a set of individuals of the same species in a specific area. Growth is conditioned by the availability of environmental resources and by other stocks in the community. All biotic and abiotic factors that limit the growth of a population are called environmental resistance.

Growth Curves

Growth curves. Exponential growth occurs under special conditions and cannot be sustained for long in nature because it reaches a point where resources are exhausted and mass mortality of individuals occurs. In natural conditions a population begins to grow exponentially until, at a point, environmental resistance slows the growth.

The value around which the number of individuals in a population stabilizes is called the ecosystem carrying capacity (K). Size indicates the maximum of a population that can be maintained more or less stably without causing degradation of the environment. Around K populations suffer fluctuations and growth becomes steady and is in equilibrium.

Reproduction: r and K Strategies

Reproducción (r strategies) are opportunistic or pioneer species living in unstable ecosystems or in the early stages of development. They have short lifespans and a high reproduction rate — examples include bacteria, algae and mosses.

K strategies describe specialist species living in stable environments. Individuals are long-lived with lower reproductive rates — examples include many large mammals and some birds.

Chemical Control: Pesticides

Chemical control: pesticides, insecticides, herbicides.

Benefits of Pesticides

1. Improve crop yields.
2. Allow the control of certain pests.

Problems with Pesticides

1. Development of resistance: Over time pests can develop resistance to products; they cease to be effective and the pest becomes more difficult to eliminate.
2. Contamination: Many of these substances pollute the environment — they can disperse through the air or deposit in the soil.
3. High persistence: Many pesticides are difficult to degrade and persist in the environment.
4. Non-selectivity: Some pesticides, besides eliminating the target pest, also eliminate beneficial flora and fauna in the ecosystem.
5. Bioaccumulation: When entering food chains, some pesticides cannot be degraded and accumulate in the tissues of living organisms.

Biological Control

Biological control: involves using living organisms as specific predators or parasites to control the population of pest species.

Natural Resources and Regeneration

Natural resources: A resource is considered a natural asset that can be exploited and whose extraction is economically viable and available. Classification depends on how long it takes to regenerate the resource:

• Renewable: regenerate in less than 100 years.
• Nonrenewable: require more than 100 years to regenerate.

Threats to Biodiversity

Dangers to biodiversity from human activities:

1. Overexploitation: when plants or animals are collected at a faster rate than they can regenerate — for example, abusive fishing.
2. Habitat destruction: contamination, indiscriminate felling, conversion to cropland or urban development, mining and public works, and industrial processes destroy habitats.
3. Introduction of invasive species: artificially introduced species can displace native populations.