Download Ecosystems - Bronx River Alliance

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:
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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.