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Chapter 50

BIOLOGY 1M03 Chapter 50: Biology Chapter 50

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McMaster University
Ben Evans

1 Chapter 50: An Introduction to Ecology  Ecology is the study of how organisms interact with their environment Areas of Ecological Study  Organismal Ecology o How individuals interact with each other and their physical environment o Researchers explore the morphological, physiological and behavioural adaptations that allow individuals to live successfully in a particular area o Also focuses on physiological adaptations that allow individuals to thrive in heat, drought, cold or other demanding physical conditions o Ex. Sockeye Salmon ▪ After spending four or five years feeding and growing in the ocean, salmon travel long distances to return to stream where they hatched ▪ Females create nests in the gravel stream bottom and lay eggs ▪ Nearby males compete for the chance to fertilize eggs as they are laid ▪ When breeding is finished, all adults die o Biologists want to know how these individuals interact with their physical surroundings and with other organisms in and around the stream ▪ Which females get best nesting sites and lay most eggs ▪ Which males are most successful in fertilizing eggs ▪ How do individuals cope with transition from living in saltwater to living in freshwater  Population Ecology o A population is a group of individuals of the same species that live in the same area at the same time o Biologists focus on how the number of individuals in a population change over time o Mathematical models of population growth have been used to predict the future of particular salmon populations o Many salmon populations have declined as their habitats have become dammed or polluted o If the factors that affect population size can be described accurately enough, mathematical models can assess the impact of proposed dams, changes in weather patterns, altered harvest levels or specific types of protection efforts  Community Ecology o A biological community consists of the species that interact with each other within a particular area o Researchers ask how species interact with each other and the consequences of those interactions ▪ May concentrate on predation, parasitism or competition 2 o Biologists might also analyze how groups of species respond to disturbances such as fires, floods and volcanic eruptions o Ex. When they are at sea, salmon eat smaller fish and are themselves hunted and eaten by orcas, sea lions, humans and other mammals ▪ When they return to freshwater to breed, they are preyed on by bears and bald eagles ▪ In both habitats, they are subject to parasitism and disease  Ecosystem Ecology o An ecosystem consists of all the organisms in a particular region along with non- living components o These physical or abiotic components include air, water and soil o Biologists study how energy and nutrients cycle through the environment o Ex. Salmon form a link between marine and freshwater ecosystems ▪ They harvest nutrients in the ocean and when they die and decompose, they transport these molecules to streams ▪ In this way, salmon transport chemical energy and nutrients from one habitat to another  Conservation biology is the effort to study, preserve and restore threatened populations, communities and ecosystems  Ecologists study how interactions between organisms and their environments result in a particular species being found in a particular area at a particular population size  Conservation biologists apply these data to preserve species and restore environments Types of Aquatic Ecosystems  An organism’s environment has both physical and biological components  The abiotic or physical components include temperature, precipitation, sunlight and wind  The biotic components consist of other members of the organism’s own species as well as individuals of other species  In aquatic ecosystems, water depth and rate of water movement qualify as key physical factors that shape the environment  Water depth dictates how much light reaches the organisms that live in a particular region  Water movement presents a physical challenge, it can sweep organisms off their feet  Freshwater Environments o Lakes and Ponds ▪ Ponds are small, lakes are large enough that the water in them can be mixed by wind and wave action ▪ Most occur in northern latitudes, formed in depressions that were created by the scouring action of glaciers thousands of years ago ▪ Water depth 3 • Littoral zone consists of the shallow waters along the shore, where flowering plants are rooted • Limnetic zone is offshore and comprises water that receives enough light to support photosynthesis • Benthic zone is made up of the substrate • Regions of the littoral, limnetic and benthic zones that receive sunlight are part of the photic zone • Portions of a lake or pond that do not receive sunlight make up the aphotic zone ▪ Water flow • Driven by wind and temperature • Littoral and limnetic zones typically much warmer and better oxygenated than benthic zone • Benthic zone is relatively nutrient rich because dead and decomposing bodies sink and accumulate there • Water from different depths can mix ▪ Organisms • Plankton (cyanobacteria, algae) live in photic zone, as do fish that eat them • Detritus (animals that consume dead organism) are common in benthic zone o Wetlands ▪ Shallow-water habitats where the soil is saturated with water for at least part of the year ▪ Water Depth • Only have shallow water and have emergent vegetation, meaning plants grow above the surface of the water • All or most of water in wetlands receive sunlight and emergent plants capture sunlight before it strikes the water ▪ Water Flow • Freshwater marshes and swamps are wetland types characterized by a slow, but steady flow of water • Bogs in contrast, develop in depressions where water flow is low or non-existent • If water is stagnant, oxygen is used up during the decomposition of dead organic matter faster than it enters via diffusion from atmosphere • As a result, bog water is oxygen poor and once oxygen is depleted, decomposition slows • Organic acids and other acids build up, lowering pH of water • At low pH, nitrogen becomes unavailable to plants 4 ▪ Organisms • Combination of acidity, lack of available nitrogen and anoxic conditions makes bogs extremely unproductive habitats • Plants in bogs are carnivorous • Marshes and swamps offer ample supplies of oxygenated water and sunlight and are very productive • Marshes lack tress and typically feature grasses (productive) • Swamps are dominated by trees and shrubs (productive) o Streams ▪ Bodies of water that move constantly in one direction ▪ Creeks are small streams, rivers are large ▪ Water Depth • Most streams are shallow enough that sunlight reaches the bottom • Availability of sunlight is usually not a limiting factor for organisms ▪ Water Flow • When it originates at a mountain glacier, lake or spring, it tends to be cold, narrow and fast • As it descends towards a lake, ocean or larger river, it accepts water from tributaries and becomes larger, warmer, slower • Oxygen levels tend to be high in fast-moving streams because water droplets are exposed to atmosphere when moving water splashes over rocks and other obstacles • Slow-moving streams tend to become relatively oxygen poor • Cold water holds more oxygen than warm water does ▪ Organisms • Rare to find photosynthetic organisms in small, fast-moving streams • Nutrient levels tend to be low and most of organic matter present consists of leaves and other materials that fall into water from outside stream • As stream widens and slows down, conditions become more favourable for growth of algae and plants and the amount of organic matter and nutrients increases o Estuaries ▪ Form where river meets ocean (freshwater mixes with saltwater) ▪ Salinity varies with changes in river flow and with proximity to ocean ▪ Salinity has drastic effect on osmosis and water balance ▪ Water Depth • Most are shallow enough that sunlight reaches substrate • May fluctuate in response to tides, storms, floods 5 ▪ Water Flow • Fluctuates daily and seasonally due to tides, storms, floods • Fluctuation is important because it alters salinity, which affects which types of organisms are present ▪ Organisms • Because water is shallow and sunlit and because nutrients are constantly being replenished by incoming river water, most productive environments on Earth o Ocean ▪ Water Depth • Intertidal zone consists of a rocky, sandy or muddy beach that is exposed to air at low tide, but submerged at high tide • Neritic zone extends from intertidal zone to depths of about 200 m o Outermost edge is defined by end of the continental shelf, gently sloping, submerged portion of a continental plate • Oceanic zone is the open ocean, deepwater region beyond continental shelft • Benthic zone is bottom of ocean • Photic zone is the intertidal and sunlit regions of neritic, oceanic and benthic zones • Areas that do not receive sunlight are in an aphotic zone ▪ Water Flow • Dominated by different processes at different depths • In intertidal zone, tides and wave action are major influences • In neritic zone, currents that bring nutrient-rich water from benthic zone of deep ocean toward shore have heavy impact ▪ Organisms • Each zone is populated by distinct species that are adapted to physical conditions present • Organisms that live in intertidal zone must be able to withstand physical pounding from waves and desiccation at low tide • Productivity is high due to availability of sunlight and nutrients contributed by estuaries as well as by currents that sweep in nutrient-laden sediments from offshore areas • Productivity is also high on outer edge of nerithic zone, due to nutrients contributed by upwellings at the edge of the continental plate Types of Terrestrial Ecosystems 6  Broad-leaved forests, deserts and grasslands are biomes, major groupings of plant and animal communities defined by a dominant vegetation type  Each biome found around the world is associated with a distinctive set of abiotic conditions  The type of biome present in a terrestrial region depends on climate, the prevailing, long-term weather conditions found in an area  Weather consists of the specific, short-term atmospheric conditions of temperature, moisture, sunlight and wind o Temperature is critical because enzymes that make life possible work at optimal efficiency only at narrow ranges of temperatures o Moisture is significant because it is required for life and because terrestrial organisms constantly lose water to the environment through evaporation o Sunlight is essential because it is required for photosynthesis o Wind is important because it exacerbates the effects of temperature and moisture  Of the four components, temperature and moisture are the most important to plants  The nature of biome that develops in a particular region is governed by o Average annual temperature and precipitation o Annual variation in temperature and precipitation  Each biome contains species that are adapted to a particular temperature and moisture regime  On land, photosynthesis and plant growth are maximized when temperatures are warm and conditions are wet  Conversely, photosynthesis cannot occur efficiently at low temperatures or under drought stress  Terrestrial Biomes o Tropical wet forest ▪ Found in equatorial regions ▪ Plants have broad leaves and are evergreen ▪ No complete, seasonal loss of leaves ▪ Temperature • High, with low variation ▪ Precipitation • Very high with high variation ▪ Vegetation • Very productive due to favourable year-round conditions • Renowned for species diversity o Subtropical deserts ▪ Found 30 degrees latitude, both north and south ▪ Temperature • High, with moderate variation ▪ Precipitation • Very low, with low variation 7 ▪ Vegetation • Scarcity of water in deserts cannot support photosynthesis so
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