BLY 303 Lecture Notes, 2011 (O Brien) Introduction to Ecology

Transcription

1 BLY 303 Lecture Notes, 2011 (O Brien) Introduction to Ecology I. Basic Concepts A. Ecology 1. Definition: study of the interactions that determine the distribution and abundance of organisms 2. Ecological question: Why does a species occur in one place, but not another? B. Distribution of species affected by abiotic and biotic factors as well as historical events 1. Abiotic factors include a. Temperature b. Rainfall c. Amount of sunlight d. Chemical content of soil and water. 2. Biotic factors involve interactions with living organisms. a. Predation b. Competition 3. Historical events a. Sever storms b. Continental Drift II. Areas of Ecology A. Organismal Ecology 1. Organismal ecologists study morphological, physiological, and behavioral adaptations that allow individuals to be successful in a particular habitat. 2. Individual salmon as an example a. Spends 4-5 years eating and growing in the ocean b. Swims hundreds to thousands of miles to return to the stream where it hatched c. Once it breeds in that streambed, the adult dies. B. Population Ecology 1. A population is a group of individuals of the same species that live in the same area at the same time. 2. How do numbers of individuals in a population change over time? 3. Salmon example a. Adult females produce 1,000s of eggs b. 98% of salmon die before they can reproduce C. Community Ecology 1. A biological community consists of the species that interact with one another in a particular area.

2 2. Community ecologists study interactions between different species in a community. 3. Example: Salmon are predators that have predators D. Ecosystem Ecology 1. An ecosystem consists of all organisms living in a certain area plus all nonliving, abiotic components such as air, water, and soil. 2. Ecosystem ecologists study how nutrients cycle and energy flows through an ecosystem 3. Example: Salmon transport nutrients from ocean to freshwater streams E. In biology the study of pollution is considered to be in the field of environmental science in other words when used by biologists ecology does NOT mean the study of pollution F. Conservation biology applies ecological concepts to preserve populations, communities, and ecosystems that are threatened. G. Dispersal 1. Movement of an individual from its birthplace 2. Types a. Jump dispersal (1) A species becomes established after moving a great distance over inhospitable habitats (2) High altitude sampling has found spiders floating over oceans using silk parachutes (3) Uganda introduced the Nile perch to Lake Victoria in 1920 as a game fish (a) (b) 2 m long, 180 kg Predator eating its way through native fish fauna b. Diffusion dispersal (1) Steady gradual expansion of a species range for many generations. (2) Ex. Fire ants have spread north, east & west since their introduction to the US in 1918 at Mobile, AL c. Secular migration (1) Timeframe: up to millions of years (2) Diffusion is so slow that natural selection has time to induce evolutionary adaptations as environments changed (3) Ex. South American llamas and vicunas are descended from an ancestral species (now extinct) that migrated from North America across the Isthmus of Panama during the Pliocene. H. Biogeography: study of how organisms are distributed in space 1. Relevant definitions a. A species that is normally found in a region is a native or an endemic species 2

3 b. A species introduced to an area where it is not normally be found is an exotic species. c. An exotic species that spreads uncontrollably is called an invasive species. [Note: All invasive species are exotics, but most exotics are not invasive] d. Biodiversity or species diversity: relative number of species in an ecosystem or habitat (1) Human activity usually lowers species diversity (2) Generally, high biodiversity is thought to lead to greater stability of an ecosystem 2. Physical barriers such as mountains or oceans can serve as barriers to dispersal a. Isthmus of Panama separates species in the tropical Atlantic Ocean from those in the tropical Pacific b. Islands lack many species common to the nearby mainland, lower species diversity 3. Geological history often explains how species came to be in a particular area a. Continental Drift (1) Isolated Australian landmass allowing evolutionary development of distinctive groups of organisms (2) Following unification of North and South America species from both continents migrated across Isthmus of Panama b. Climate change such as droughts and glaciations can affect speciation by isolating populations (1) Mountain tops (2) River systems (3) The much older Appalachian Mountains harbor a greater species diversity than do the Rocky and Sierra Nevada Ranges c. Humans by transporting seeds, insects, etc. across physical barriers have accounted for the introduction of a tremendous number species to new habitats (1) Fire ants (2) Kudzu 4. The distribution of species can be limited by biotic (= living organisms) factors. a. Interactions with other species can limit dispersal. b. Example: The range of domestic cattle in Africa has been limited by the tsetse fly, which transmits a deadly parasite. 5. Often, exotic species fail to thrive in the new environment due to abiotic (= non-living) factors. a. An area may simply be too cold or too warm for the exotic species. 3

4 b. Example: kudzu thrives in the Southeast U.S., but cannot survive the colder winters of the northern and western U.S. III. Types of Terrestrial Ecosystems A. Biome 1. Extremely large terrestrial ecosystem 2. Characterized by distinct vegetation 3. Characteristics of biomes determined by climate (temperature and precipitation) B. Major types 1. Tropical rain forests a. Equatorial regions b. Temperatures and rainfall are high. c. No seasons, plants grow all year long. d. High primary productivity with high biomass. (1) Productivity = total amount of photosynthesis / unit area / year. (2) Aboveground biomass = total mass of living plants, excluding roots. e. Highest levels of biodiversity on the planet. 2. Tundra a. Polar regions and high elevations b. Prolonged periods of cold, only 6-8 weeks of temps above freezing c. Little precipitation d. Treeless, low primary productivity 3. Deserts a. Bands about 30 degrees of latitude north & south of the Equator b. Mean monthly temperatures vary, but rarely fall below freezing. c. Low annual precipitation. (1) Productivity is very low. (2) Plants are widely spaced due to competition for water. 4. Temperate forests a. Hot summers and cold winters b. Precipitation is high and relatively constant. (1) Angiosperm trees dominate. (2) Plant growth slow in winter. c. Productivity and biodiversity are moderate 5. Boreal forests a. South of Arctic Circle b. Temperature variation extreme (>70 C) with very cold winters and moderate summers c. Gymnosperm forests 4

5 d. Low productivity, low biodiversity, but high biomass 6. Grasslands, prairies or steppes a. Too dry and too many lightening fires for trees b. Soils high in nutrients c. Ideal for farming IV. Aquatic Ecosystems A. Freshwater environments 1. Wetlands are shallow water habitats a. Soil is saturated with water most of the year b. Characterized by emergent vegetation that grows above the surface 2. Ponds are small bodies of standing water 3. Lakes are deep a. Water stratified into different layers in winter and summer b. Neither ponds nor lakes have emergent vegetation 4. Streams and rivers a. Bodies of water that move in one direction. b. Characteristics change along its length. (1) At its mountain origin, a stream is cold and fast. (2) By the time it flows into the ocean or a lake, it has become warm and slow B. Estuaries 1. Streams and rivers meet oceans 2. Freshwater and saltwater mix. 3. Low biodiversity because few organisms can withstand the extreme fluctuations in salinity 4. High productivity because nutrient input is high V. Marine environments 1. The intertidal or littoral zone is a shallow region along the shore. a. Environment of extremes (1) Organisms exposed to air and sun during low tide (2) Organisms covered with water at high tide. b. Substrate is often unstable due to wave action 2. The neritic zone extends from the intertidal zone toward the ocean to depths of about 200 m. a. This zone is still relatively productive because nutrients well up from the ocean depths. b. Many fish live in the neritic zone, and most coral reefs are found in these areas. 3. The oceanic zone consists of the open ocean and is one of the most unproductive ecosystems on Earth. 5