Environmental Science: Toward A Sustainable Future Chapter 4 Ecosystems: Populations and Succession

This Lesson Identifies The Forces That Change Ecosystems How biotic potential and environmental resistance control population growth. Ecological succession: primary and secondary. The third and fourth principles of ecosystem sustainability. How humans influence the rate and direction of ecosystem change.

Population Equilibrium BirthsDeaths A balance between births and deaths.

Population Growth Curves

Population Dynamics Biotic potential: ability of populations to increase Reproductive rate Migration and dispersal Defenses Coping strategies

Population Dynamics Reproductive strategies: Many offspring with low parental care Few offspring with high parental care

Population Dynamics Environmental resistance: combination of biotic and abiotic factors that may limit population increase Predators, competitors, disease Adverse weather, limited food/nutrients

Biotic Potential Vs. Environmental Resistance

Population Dynamics Factors of environmental resistance are either: Density-independent: effect does not vary with population density; e.g., adverse weather Density-dependent: effect varies with population density; e.g., infectious disease

Predator-prey Balance:Wolves and Moose

Tipping the Balance: Introduced Species Rabbits in Australia Domestic cats on islands Zebra mussels in the great lakes

Introduced Species Why have these introductions resulted in a degradation of the ecosystems? (Think in terms of environmental resistance and biotic potential.)

Mechanisms of Population Equilibrium Territoriality: defense of a resource against individuals of the same species Examples of wolves and songbirds Results in priority use of resources

The Fourth Principle of Ecosystem Sustainability The size of the consumer population is maintained so that overgrazing or other overuse does not occur.

Mechanisms of Population Equilibrium: Plant-Herbivore

Compare the predator-prey with plant- herbivore methods of controlling the size of the herbivore population. How would the herbivore population growth curve look if diseases were used as the control mechanism?

Mechanisms of Population Equilibrium Absence of natural enemies like predators allows a herbivore population to exceed carrying capacity which results in overgrazing of the habitat. The herbivore population subsequently crashes.

Mechanisms of Population Equilibrium: Plant Diversity Microclimates Specialized adaptations Balanced herbivory

Balanced Herbivory

Disturbance and Succession Equilibrium theory: ecosystems are stable environments in which the biotic interactions among species determine the structure of the communities present.

Succession and Disturbance Ecological succession: transition between biotic communities Primary- no previous biotic community Secondary- previously occupied by a community Aquatic- transition from pond or lake to terrestrial community

Primary Succession Mosses invade an area and provide a place for soil to accumulate. Larger plants germinate in the new soil layer resulting in additional soil formation. Eventually shrubs and trees will invade the area.

Secondary Succession

Aquatic Succession

The Fifth Principle of Ecosystem Sustainability Ecosystems show resilience during a disturbance

Disturbance Removes organisms Reduces populations Creates opportunities for other species to colonize

Fire and Succession

Fire climax ecosystems: dependent upon fire for maintenance of existing balance; e.g., grasslands, pine and redwood forests What significance does this have for humans and where they live?

Resilience Mechanisms After A Forest Fire Nutrient release to soil Regrowth by remnant roots and seeds Invasions from neighboring ecosystems Rapid restoration of energy flow and nutrient cycling

Human Impacts Increased our biotic potential Decreased our environmental resistance Contributed to the degradation of ecosystems

Human Impacts Introduce species Eliminate natural predators Alter abiotic factors Misunderstand the role of fire Reduce biodiversity

Implications For Humans Protecting and managing the natural environment to maintain the goods and services vital to human economy and survival. Establishing a balance between our own species and the rest of the biosphere.

Four Principles of Ecosystem Science Ecosystems will change over time Individual species and interactions between species will have important impacts on ecological processes Different sites and regions are unique (abiotic and biotic characteristics) Disturbances are important and frequent events that have a profound impact on the ecosystem

Fifth Principle of Ecosystem Sustainability Ecosystems depend on biodiversity.

Why is the fifth principle of sustainability important in understanding the following issues? Endangered species Agriculture Biotechnology Medicine