An Introduction to Ecology

1. An Introduction to Ecology 50

2. Key Concepts • Ecology’s goal is to explain the distribution and abundance of organisms. It is the branch of biology that provides a scientific foundation for conservation efforts. • Physical structure—particularly water depth—is the primary factor that limits the distribution and abundance of aquatic species. Climate—specifically, both the average value and annual variation in temperature and in moisture—is the primary factor that limits the distribution and abundance of terrestrial species.

3. Key Concepts • Climate varies with latitude, elevation, and other factors—such as proximity to oceans and mountains. Climate is changing rapidly around the globe. • A species’ distribution is constrained by historical and biotic factors, as well as by abiotic factors such as physical structure and climate.

4. Introduction • Ecologyis the study of how organisms interact with their environment. • The central goal of ecology is to understand the distribution and abundance of organisms.

5. Areas of Ecological Study • To understand why organisms live where they do and in what numbers, biologists break ecology into several levels of analysis. • In ecology, researchers work at four main levels: • Organisms. • Populations. • Communities. • Ecosystems.

6. Organismal Ecology • Organismal ecologists explore the morphological, physiological, and behavioral adaptations that allow individual organisms to live successfully in a particular area.

7. Population Ecology • A population is a group of individuals of the same species that lives in the same area at the same time. • Population ecologists focus on how the numbers of individuals in a population change over time.

8. Community Ecology • A biological community consists of the species that interact with one another within a particular area. • Community ecologists study the nature and consequences of the interactions between species and the consequences of those interactions. • The work might concentrate on predation, parasitism, and competition, or explore how groups of species respond to fires, floods, and other disturbances.

9. Ecosystem Ecology • An ecosystem consists of all the organisms in a particular region, along with nonliving, or abiotic, components. • Ecosystem ecologists study how nutrients and energy move among and between organisms and the surrounding atmosphere and soil or water. • Because humans are affecting energy flows and climate, this work has direct public policy implications.

15. How Do Ecology and Conservation Efforts Interact? • The four levels of ecological study are synthesized and applied in conservation biology. • 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.

16. Types of Aquatic Ecosystems • An organism’s environment has both physical and biological components. • The abiotic components include temperature, precipitation, wind, and sunlight. • The biotic (living) components consist of other members of the organism’s own species, as well as individuals of other species. • In freshwater and salt water, three key physical factors affect the distribution and abundance of organisms: nutrient availability, water depth, and water movement.

17. Nutrient Availability • Nutrients tend to be washed away in moving water, and fall to the bottom in still water, and thus are in short supply in many aquatic ecosystems. • Nutrient levels are important because they limit growth rates in the photosynthetic organisms that provide food for other species. • Ocean upwelling and lake turnover affect nutrient availability by bringing nutrients from the bottom up to the water surface.

18. Ocean Upwelling • In the oceans, nutrients in the sunlit surface waters are constantly lost in the form of dead organisms that rain down into the depths. In certain coastal regions of the world’s oceans, however, nutrients are brought up to the surface by currents that cause upwellings. • As the surface water moves away from the coast, it is steadily replaced by water moving up from the ocean bottom. • The upwelling water is nutrient rich.

20. Lake Turnover • Each year, glacially formed lakes undergo spring and fall turnovers. • In winter and summer, the temperature in these lakes varies from top to bottom along a gradient called a thermocline. • In winter, surface water is colder while the water at the bottom is warmer. • In the summer, surface water is warmer while the water at the bottom is colder. • The surface water in winter and summer is oxygen rich, while the water at the bottom is nutrient rich.

21. Lake Turnover • The oxygen-rich surface water either warms (in spring) or cools (in fall) to 4ºC—the temperature at which water is most dense—and sinks to the bottom, carrying oxygen down to the bottom and driving nutrients up to the surface. • Without the spring and fall turnovers, most freshwater nutrients would remain on the bottom of lakes. These aquatic ecosystems would be much less productive, as a result.

23. Water Flow • The rate of water movement and water depth are the key physical factors that shape the environments in aquatic ecosystems. • Water movement is a critical factor in aquatic ecosystems because it presents a physical challenge. It can literally sweep organisms off their feet.

24. Water Depth • Water depth dictates how much light reaches the organisms that live in a particular region. • Water absorbs and scatters light, so the amount and types of wavelengths available to organisms change dramatically as water depth increases, as does light intensity. • Light has a major influence on productivity—the total amount of carbon fixed by photosynthesis per unit area per year.

28. Freshwater Environments: Lakes and Ponds • Lakes and ponds are distinguished by size—ponds are small; lakes are large enough that the water in them can be mixed by wind and wave action. • Lakes and ponds have five zones of water depth.

29. Water Depth Zones in Freshwater Environments • The littoral (“seashore”) zone consists of the shallow waters along the shore, where flowering plants are rooted. • The limnetic (“lake”) zone is offshore and comprises water that receives enough light to support photosynthesis. • The benthic (“depths”) zone is made up of the bottom, or substrate. • Regions of the littoral, limnetic, and benthic zones that receive sunlight are part of the photiczone. • Portions of the lake or pond that do not receive sunlight make up the aphoticzone.

31. Freshwater Environments: Lakes and Ponds • Water movement in lakes and ponds is driven by wind and changes in temperature. • Cyanobacteria, algae, and other microscopic organisms, collectively called plankton, live in the photic zone, as do the fish and small crustaceans that eat them. • Animals that consume dead organic matter, or detritus, are found in the benthic zone.

32. Freshwater Environments: Wetlands • Wetlands are shallow-water habitats where the soil is saturated with water for at least part of the year, and contain indicator plants that only grow in saturate soils. • Wetlands are distinct from lakes and ponds because they have only shallow water, and they have emergent plants that grow above the surface of the water.

33. Freshwater Environments: Wetlands • Wetland types are distinguished by water flow and vegetation. • Bogs have low or nonexistent water flow, and are stagnant, acidic, and nonproductive. • Freshwater marshes and swamps have a slow but steady flow of water and are relatively nutrient rich and highly productive. • Marshes have nonwoody plants. • Swamps are dominated by trees and shrubs.

38. Freshwater Environments: Streams • Streams move constantly in one direction. Creeks are small streams; rivers are large. • Most streams are shallow enough that sunlight reaches the bottom. • The structure of a typical stream varies along its length. • Where it originates, it tends to be cold, narrow, and fast; at the end, it tends to be warmer, wider, and slower. • Streams thus tend to have fewer organism types near their source (mostly animals) and more varied types near their end (algae, plants, and animals).

40. Freshwater/Marine Environments: Estuaries • An estuary forms where a river meets the ocean and freshwater mixes with salt water. • An estuary includes slightly saline marshes as well as the body of water that moves in and out of these environments. • Salinity varies withchanges in river flows and with proximity to the ocean. • Salinity has dramatic effects on osmosis and water balance; species that live in estuaries have adaptations that allow them to cope with variations in salinity.

41. Freshwater/Marine Environments: Estuaries • Most estuaries are relatively shallow, but water depth may vary dramatically. • Water flow fluctuates daily and seasonally due to tides, storms, and floods. This fluctuation alters salinity. • Species that live in estuaries have adaptations that allow them to cope with variations in salinity. Estuaries are among the most productive environments.

43. Marine Environments: The Oceans • The world’s oceans form a continuous body of salt water. Regions within an ocean can vary markedly in their physical characteristics. • In terms of water depth, the ocean has six regions: • The intertidal zone consists of a beach that is exposed to the air at low tide but submerged at high tide. • The neritic zone extends from the intertidal zone to depths of about 200 m. Its outermost edge is defined by the end of the continental shelf—the gently sloping, submerged portion of a continental plate.

44. Marine Environments: The Oceans • The oceanic zone is the “open ocean”—the deepwater region beyond the continental shelf. • The bottom of the ocean is the benthic zone. • The intertidal and sunlit regions of the neritic, oceanic, and benthic zones make up a photic zone. • Areas that do not receive sunlight are in an aphotic zone.

46. Marine Environments: The Oceans • Water movement in the ocean is dominated by different processes at different depths. • Each zone in the ocean is populated by distinct species that are adapted to the physical conditions present. • The intertidal and neritic zones are the most productive; the neritic zone includes coral reefs, which are among the most productive environments on Earth. • The photic and aphotic zones are not as productive.

47. Types of Terrestrial Ecosystems • Biomes are major groupings of plant and animal communities defined by a dominant vegetation type. • Each biome 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 specific short-term atmospheric conditions. • Climate and weather consist of temperature, moisture, sunlight, and wind.

49. Types of Terrestrial Ecosystems • The nature of the biome that develops in a particular region is governed by: • The average annual temperature and precipitation. • The annual variation in temperature and precipitation. • Temperature and moisture influence net primary productivity (NPP)—the total amount of carbon that is fixed per year minus the amount of fixed carbon oxidized during cellular respiration.

50. Types of Terrestrial Ecosystems • NPP represents the organic matter that is available as food for other organisms. • In terrestrial environments NPP is often estimated by measuring abovegroundbiomass, the total mass of living plants, excluding roots. • 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.