Environmental Science PowerPoint Lecture Principles of Environmental Science - Inquiry and Applications, 1st Edition by William Cunningham and Mary Ann Cunningham

Chapter 3 - Topics Who Lives Where, and Why? Species Interactions Community Properties Communities in Transition

Part 1: Who Lives Where, and Why?

Tolerance Limits Each environmental factor (temperature, nutrient supply, etc.) has both minimum and maximum levels beyond which a species cannot survive or is unable to reproduce.

Abundance and Distribution of Species Liebig - proposed that the single environmental factor in shortest supply relative to demand is the critical determinant in species distribution Shelfold - added to Liebig’s work by proposing that the single environmental factor closest to tolerance limits determines where a particular organism can live

Today we know that for many species the interaction of several factors, rather than a single limiting factor, determines biogeographical distribution. Sometimes, the requirements and tolerances of species are useful indicators of specific environmental characteristics.

Adaptation and Natural Selection Two types of adaptation: Acclimation - changes in an individual organism due to non-permanent physiological modifications Evolution - gradual changes in a species due to changes in genetic material and competition Theory of evolution - developed by Charles Darwin and Alfred Wallace.

Natural selection - genetic combinations best adapted for present environmental conditions tend to become abundant Spontaneous, random mutations Selective pressure - physiological stress, predation, competition, luck

Speciation These 13 species of finches are descendents of a single seed-eating species.

The Taxonomic Naming System

Habitat - the place or set of environmental conditions in which a particular organism lives Ecological niche - the role played by a species in a biological community The Ecological Niche

Resource Partitioning Over time, niches can evolve as species develop new strategies to exploit resources. Law of Competitive Exclusion: No two species will occupy the same niche and compete for the same resources in the same habitat for very long.

Part 2: Species Interactions Predation and competition - antagonistic relationships

Three Types of Symbiosis: Commensalism - one member benefits, while the other is neither benefited nor harmed Mutualism - both members of the partnership benefit Parasitism - one species benefits and the other is harmed

Defensive Mechanisms

Batesian Mimicry

Keystone species - species that play essential community roles (examples: mycorrhizae, giant kelp)

Part 3: Population Growth Exponential growth - the unrestricted increase in a population (also called the biotic potential of a population) Carrying capacity - the maximum number of individuals of any species that can be supported by a particular ecosystem on a sustainable basis

Overshoots and Diebacks

Population Oscillations

Growth to a Stable Population

Environmental Resistance Environmental resistance - factors that tend to reduce population growth rates Density-dependent - linked to population size - disease, lack of food Density-independent - often environmental - droughts, floods, habitat destruction Intrinsic - attributes of a species - slow reproduction Extrinsic - external to a species - predators, competitors, environmental risks

Part 3: Community Properties Primary productivity - a community’s rate of biomass production, or the conversion of solar energy into chemical energy stored in living (or once-living organisms) Net primary productivity - primary productivity minus the energy lost in respiration Productivity depends on light levels, temperature, moisture, and nutrient availability.

Relative biomass accumulation of major world ecosystems.

Abundance and Diversity Abundance - the number of individuals of a species in an area Diversity - the number of different species in an area A useful measure of the variety of ecological niches or genetic variation in a community Decreases as we go from the equator towards the poles Abundance and diversity depend on total resource availability in an ecosystem.

Antarctic Marine Food Web Complexity - the number of species at each trophic level and the number of trophic levels in a community

Stability and Resilience Stability - a dynamic equilibrium among the physical and biological factors in an ecosystem or a community Resiliency - the ability to recover from disturbance Three kinds of stability or resiliency in ecosystems: Constancy - lack of fluctuations in composition or functions Inertia - resistance to perturbations Renewal - ability to repair damage after disturbance

Community structure Distribution of members of a population in a given space can be: Random - individuals live wherever resources are available Ordered - often the result of biological competition Clustered - individuals of a species cluster together for protection, mutual assistance, reproduction, or to gain access to a particular environmental resource

Edges and Boundaries Ecotones- the boundaries between adjacent habitats Often rich in species diversity Example: the boundary between a forest and a meadow

Edge effects - the environmental and biotic conditions at the edge of a habitat Temperature, moisture levels, predator species, etc. Edge effects associated with habitat fragmentation are generally detrimental to species diversity. Core habitat - the interior area of a habitat Habitat not impacted by edge effects Some species avoid edges and ecotones and prefer interior environments. Edge vs. Core

Part 4: Communities in Transition Ecological succession - the process by which organisms occupy a site and gradually change environmental conditions by creating soil, shelter, shade, or increasing humidity Primary succession - occurs when a community begins to develop on a site previously unoccupied by living organisms Secondary succession - occurs when an existing community is disrupted and a new one subsequently develops at the site

Primary Succession on Land

Climax Community Climax community - a community that develops in primary or secondary succession and seemingly resists further change Clements: succession to a climax community is like a parade or relay, in which species replace each other in predictable groups and in a fixed, regular order Gleason: succession is individualistic and unpredictable

Disclimax (equilibrium) community - community characterized by, and adapted to, periodic disruption Example: fire-climax communities

Introduced Species and Community Change

Exotic Species Sometimes communities can be completely altered by the introduction of exotic species. Exotic species are often introduced by humans. Successful exotics tend to be prolific, opportunistic species, such as goats, cats, and pigs. Many ecologists consider exotic species invasions the most pressing hazard for biological communities in the coming century.