Concept 41.1   Ecological Systems Vary over Space and Time

• An ecological system, or ecosystem, consists of one or more organisms and the biotic and abiotic components of the environment with which they interact.
• Ecological interactions lead to evolution by natural selection.
• Ecological systems can be studied at scales in the biological hierarchy ranging from an individual organism and its immediate surroundings to populations, communities, landscapes, or the entire biosphere.
• Ecological systems are highly complex and variable but can be understood with scientific methods.

Concept 41.2   Solar Energy Input and Topography Shape Earth’s Physical Environments

• Weather is the state of atmospheric conditions in a particular place at a particular time, and climate is their average state and pattern of variation over longer periods.
• Latitudinal differences in solar energy input are caused by differences in the angle of the sun’s incoming rays. Seasonality results from the tilt of Earth’s axis of rotation relative to its orbit around the sun. Review Figure 41.3 and Figure 41.4
• Latitudinal differences in solar energy input drive north–south patterns of atmospheric circulation. These patterns, in turn, influence latitudinal patterns of temperature and precipitation and distribute heat from low to high latitudes. Review Figure 41.5
• Prevailing winds result from the interaction of north–south atmospheric circulation with Earth’s eastward rotation, which adds an east–west component to air movement because of the Coriolis effect. Review Figure 41.6
• Oceanic circulation patterns called gyres are caused by prevailing surface winds and by the Coriolis effect. These patterns redistribute heat from low to high latitudes and influence patterns of temperature and precipitation. Review Figure 41.7
• Variation in the elevation of Earth’s surface, known as topography, affects the physical environment. Review Figure 41.8 and ANIMATED TUTORIAL 41.1
• Climate diagrams summarize climate at a particular location in an ecologically relevant way. Review Figure 41.9

Concept 41.3   Biogeography Reflects Physical Geography

• A biome is a distinct physical environment that is inhabited by ecologically similar organisms with similar adaptations. The species that occupy the same biome in geographically separate regions may not be closely related phylogenetically but often show convergent adaptations.
• The distribution of terrestrial biomes is broadly determined by annual patterns of temperature and precipitation. Review Figure 41.10, Figure 41.11 and ANIMATED TUTORIAL 41.2
• Other features of the physical environment—particularly soil characteristics—interact with climate to influence the character of terrestrial vegetation. Review Figure 41.12
• Climate is less important in distinguishing aquatic biomes than are water depth and flow, temperature, pressure, salinity, and characteristics of the substrate. Review Table 41.1 Part 1, Table 41.1 Part 2, Figure 41.13, and ANIMATED TUTORIAL 41.3

Concept 41.4   Biogeography Also Reflects Geological History

• Alfred Russel Wallace first noticed a boundary between two distinct assemblages of terrestrial species, now known as Wallace’s line, that reflected a barrier to dispersal, rather than a boundary between climates or soils.
• The world can be divided into biogeographic regions, each of which contains a distinct assemblage of species, many of which are phylogenetically related. Review Figure 41.14 and ACTIVITY 41.1
• The boundaries of biogeographic regions generally correspond to present or past barriers to dispersal and can be explained by continental drift. Review Figure 41.15
• Biogeographers use phylogenetic information, in conjunction with the fossil record and geological history, to determine how the modern distributions of organisms came about.

Concept 41.5   Human Activities Affect Ecological Systems on a Global Scale

• Humans have converted almost half of Earth’s land area into human-dominated ecosystems, which are much more homogenous and less complex than natural ecosystems. Remaining natural ecosystems occur in small, isolated fragments.
• Humans move species around the globe without regard to natural barriers to dispersal. These movements are homogenizing the biota of the planet.
• Conservation ecology and restoration ecology are new subdisciplines of ecology whose goals are to prevent extinction of species and to restore damaged ecosystems.
• Knowledge of natural history is essential to these subdisciplines, as it is to all ecological inquiry.