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Transcript
BACKGROUND INFORMATION Ecosystems An ecosystem is defined as a community of different species interacting with one another and with the chemical and physical factors that make up its non-living environment. Lessons in this section will guide educators, students and other visitors to the Bronx River in an exploration of ecosystems. Walking the Bronx River Forest and Organism Survey share some guidelines for those who intend to share their discovery of species and/or spaces with others. Please see the Background Information segment below for an overview of the major components of ecosystems. TERMS OF INTEREST Biodiversity, biotic, abiotic, producers, consumers, autotrophs, heterotrophs, herbivores, carnivores, omnivores. BACKGROUND INFORMATION: Ecosystems can be divided into two parts: abiotic – or non-living components (water, air, nutrients and solar energy), and biotic – or living components (plants, animals, microorganisms). Abiotic The abiotic parts are physical and chemical factors that influence living organisms in terrestrial ecosystem and aquatic life zones. Different species thrive under different physical conditions such as amount of sunlight, precipitation and/or temperature range. Each population in an ecosystem has a range of tolerance, beyond which none can survive. Most organisms are least tolerant during juvenile or reproductive stages of their life cycles. A variety of factors can affect the number of organisms in a population. However, sometimes one factor is more important in regulating population growth than other factors. On land, precipitation is often the limiting factor. Though the Bronx is not a desert climate, the watershed is heavily impacted by drought events. Droughts reduce food and water for animals, degrade the quality of soil, threaten trees and have the potential to dry up wetland areas. At the Bronx River, trees like the black willow rely heavily on moisture brought by the river. When drought persists for a significant time period, the river becomes narrow and shallower and deprives the trees. Additionally, the water may become warmer and less oxygenated, which can harm or kill the fish, damselflies, and other organisms that absorb oxygen from the water. The floodplain relies on periodic flooding to replenish moisture and nutrients. Conversely, heavy precipitation brings a host of other problems to the Bronx River. As water falls onto the mostly impervious surfaces of the Bronx, it rushes down to sewers and the river, picking up any loose soils, chemicals, nutrients and debris in its path, causing erosion and increasing water pollution. Storm water runoff causes combined sewer overflows, which dump billions of gallons of untreated sewage and polluted storm water into the Bronx River and other NYC waterways each year. (See Speak Up for a Clean Bronx River! In the ISSUES AND ACTION section of this guide for details.) Further, excessive salt runoff from the Bronx River Parkway in winter can kill plants and animals living in and along the freshwater section of the river. In addition to salinity and pollution, important limiting abiotic factors for aquatic ecosystems include temperature, sunlight, dissolved oxygen content and nutrient availability. Biotic Living organisms capture and transform matter and energy from their environment to supply their needs for survival, growth, and reproduction. The complete set of chemical reactions that carries out this role in cells and organisms is called metabolism. Living organisms in ecosystems usually are classified as either producers or consumers. Producers, sometimes called autotrophs, make their own food from compounds obtained from their environment. All other organisms are consumers, which depend directly or indirectly on food provided by the producers. On land, most producers are green plants. In freshwater, tidal, and marine ecosystems, algae and plants are the major producers near shorelines. (In open ocean, the dominant producers are the phytoplankton that float or drift in the water.) Most producers capture sunlight to make carbohydrates and other complex organic compounds from abiotic nutrients in the environment. The process for using sunlight to make carbohydrates is called photosynthesis. Some specialized bacteria can convert simple compounds to more complex nutrient compounds without sunlight through a process known as chemosynthesis. Jose, the Bronx River Beaver, 2007. Wildlife Conservation Society / Bronx Zoo Consumers, also known as heterotrophs, get their energy and nutrients by feeding on other organisms and their remains. They are classified as such: • Primary consumers/Herbivores – Plant eaters; feed directly on producers. e.g. muskrat, beaver, spicebush swallowtail caterpillar • Secondary consumers/Carnivores – meat eaters; feed on other consumers. e.g. insect eating birds such as yellow warbler, red-bellied woodpecker • Tertiary, or high-level consumers feed on other carnivores. e.g. Cooper’s hawk • Omnivores – eat both plants and animals. e.g. raccoon • • You can make your own food web using Bronx River organisms! See the species list in the RESOURCES section of this guide or view the 2005 Bronx River BioBlitz list at: http://www.bronxriver.com/BioBlitz.cfm Scavengers – feed on dead organisms. Detrivores – feed on detritus, or parts of dead organisms and cast off fragments and wastes of living organisms. There are two principle types: ß ß Detritus feeders – extract nutrients from partly decomposed organic matter in leaf litter, plant debris and animal dung. Decomposers – recycle organic matter in ecosystems by breaking down dead organic material to get nutrients and release the simpler compounds into the soil and water where they can be utilized by other organisms. The survival of any individual organism depends on the flow of matter and energy through its body. However, an ecosystem as a whole survives primarily through a combination of matter cycling and one-way energy flow. Food Webs Organisms interact in their nonliving environment in many ways. Whether dead or alive, they are potentially food or shelter for another organism. Many can imagine a predatorÆ prey food chain. In nature, these simplified food chains are interlocked with many other chains and the biochemical processes that sustain them, forming a food web. Why is biodiversity so important? The key to a healthy food web is biodiversity. Biodiversity is a variable contributing to the biological health of an area. It is the variety of different species (species diversity), the genetic variability of individuals within each species (genetic diversity), variety of habitats (ecological diversity), and functions such as energy flow and matter cycling needed for the survival of species and biological communities (functional diversity). This great variety of genes, species, biological communities and biological processes gives us food, wood, medicines, fibers, energy and more that keep people alive and drive our economy. These same biological communities provide ecological services such as water purification, flood control, soil recharging, pest control, and recycling of matter. All species contain genetic information that represents thousands to millions of years of adaptation to the earths changing environmental conditions. These species are the raw material for future adaptations. Loss of biodiversity reduces the availability of ecosystem services and decreases the ability of species, communities and ecosystems to adapt to environmental conditions. Biodiversity is nature’s “insurance policy” against disasters. Human Impact Humans have modified natural ecosystems by: • Fragmenting habitat by dividing habitats with roadways, buildings and other people-scapes. • Causing environmental degradation by dumping chemicals, nutrients and garbage. • Simplifying natural ecosystems by increasing impervious surfaces (e.g., roadways, rooftops, parking lots) and straightening, dredging and/or channeling the river with bulkheads. This creates less riverbank diversity (less inviting to a variety of species) and increases erosion while pushing sediments away from the banks and out to the Long Island Sound. • Creating monocultures with non-native landscaping such as lawns and groves. This has invited opportunistic species such as porcelain berry. • Causing pesticide resistance in insects, bacteria and other pests by using pesticides and antibiotics. • Eliminating some predators. Bear, bobcat and wolf used to roam this area. • Deliberately or accidentally introducing new or non-native species. • Over-harvesting renewable resources such as trees along the river. • Interfering with the normal chemical cycling and energy flows in systems. Conservation biologists are concerned about the biodiversity of the Bronx River Watershed for these very reasons. They ask: “What measures can we take to ensure that ecosystem functions and viable populations of wild species can be sustained?” Biodiversity is necessary to all life on earth, including human life. When humans cause or hasten the extinction of wildlife populations and species or disrupt vital ecological processes, they are affecting the very system that keeps them healthy and alive. The best way to preserve the earth’s biodiversity and ecological functions is to protect intact ecosystems that provide sufficient habitat for sustaining natural populations of species, including us. What can you do to help maintain or increase the biodiversity of the Bronx River? Learning about ecosystems and the other aspects of the Bronx River Watershed is a great start. Inspiring others to do so is a further step. To see what some people are doing see the Take Action! piece in the ISSUES AND ACTION section of this guide.