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 The life cycle of a tapeworm begins when eggs or tapeworm segments in the feces are ingested by pigs or humans. The embryos hatch, penetrate the intestinal wall, and circulate to the musculature in both pigs and humans. This figure shows how humans may acquire a tapeworm infection by ingesting raw or undercooked meat. Infection may results in cysts in the musculature, or in tapeworms in the intestine. Tapeworms attach themselves to the intestine via a hook-like structure called the scolex. Tapeworm segments and eggs are excreted in the feces, completing the cycle.
This diagram shows the life cycle of the tapeworm, a human worm parasite. (credit: modification of work by CDC)

Concept in action

To learn more about “Symbiosis in the Sea,” watch this webisode of Jonathan Bird’s Blue World.

Characteristics of communities

Communities are complex systems that can be characterized by their structure (the number and size of populations and their interactions) and dynamics (how the members and their interactions change over time). Understanding community structure and dynamics allows us to minimize impacts on ecosystems and manage ecological communities we benefit from.

Biodiversity

Ecologists have extensively studied one of the fundamental characteristics of communities: biodiversity. One measure of biodiversity used by ecologists is the number of different species in a particular area and their relative abundance. The area in question could be a habitat, a biome, or the entire biosphere. Species richness is the term used to describe the number of species living in a habitat or other unit. Species richness varies across the globe ( [link] ). Ecologists have struggled to understand the determinants of biodiversity. Species richness is related to latitude: the greatest species richness occurs near the equator and the lowest richness occurs near the poles. Other factors influence species richness as well. Island biogeography attempts to explain the great species richness found in isolated islands, and has found relationships between species richness, island size, and distance from the mainland.

Relative species abundance is the number individuals in a species relative to the total number of individuals in all species within a system. Foundation species, described below, often have the highest relative abundance of species.

 Map shows the special distribution of mammal species richness in North and South America. The highest number of mammal species, 179-228 per square kilometer, occurs in the Amazon region of South America. Species richness is generally highest in tropical latitudes, and then decreases to the north and south, and is at zero in the Arctic regions.
The greatest species richness for mammals in North America is associated in the equatorial latitudes. (credit: modification of work by NASA, CIESIN, Columbia University)

Foundation species

Foundation species are considered the “base” or “bedrock” of a community, having the greatest influence on its overall structure. They are often primary producers, and they are typically an abundant organism. For example, kelp, a species of brown algae, is a foundation species that forms the basis of the kelp forests off the coast of California.

Foundation species may physically modify the environment to produce and maintain habitats that benefit the other organisms that use them. Examples include the kelp described above or tree species found in a forest. The photosynthetic corals of the coral reef also provide structure by physically modifying the environment ( [link] ). The exoskeletons of living and dead coral make up most of the reef structure, which protects many other species from waves and ocean currents.

 Photo shows pink brain-like coral and long, finger-like coral growing on a reef. Fish swim among the coral.
Coral is the foundation species of coral reef ecosystems. (credit: Jim E. Maragos, USFWS)

Keystone species

A keystone species    is one whose presence has inordinate influence in maintaining the prevalence of various species in an ecosystem, the ecological community’s structure, and sometimes its biodiversity. Pisaster ochraceus , the intertidal sea star, is a keystone species in the northwestern portion of the United States ( [link] ). Studies have shown that when this organism is removed from communities, mussel populations (their natural prey) increase, which completely alters the species composition and reduces biodiversity. Another keystone species is the banded tetra, a fish in tropical streams, which supplies nearly all of the phosphorus, a necessary inorganic nutrient, to the rest of the community. The banded tetra feeds largely on insects from the terrestrial ecosystem and then excretes phosphorus into the aquatic ecosystem. The relationships between populations in the community, and possibly the biodiversity, would change dramatically if these fish were to become extinct.

Questions & Answers

Cellular respiration
Lucy Reply
what are the characteristics of living things
Ruth Reply
Movement Respiration Nutrition/Feeding Irritability/Sensitivity Growth Excretion Reproduction Deat/Life span
Hashim
What makes children from the same father and mother sometimes don't look alike?
Hashim
identification of problems
Nana Reply
what happens in the process of raising the human arms
Nana
what is biology
Brandi Reply
first step in scientific method
Brandi
In an investigation the pancreatic duct of a mammal was blocked.It was found that the blood sugar regulation remained normal while food digestion was impaired.Explain
Mac Reply
To begin with, obstruction of pancreatic duct will alter the blood sugar level as the juices responsible for glucose regulation will be rendered inconsequential. This will in turn affect the rate of digestion and absorbtion of digested food substances by the Villus .
Muktar
characteristics of algae
OMIME Reply
Algae are eukaryotic organisms. Algae do not have roots and stems. Algae have chlorophyll and helps in carrying out photosynthesis.
Aditi
Cell wall is the rigid layer enclosed by membranes of plants and prokayortic cell, it maintains the shape of the cell and serve as a protective barrier.
chizoba Reply
ECOLOGY: is a branch of biology that studies the interactions among organisms and their biophysical environment, which includes both biotic and abiotic components. 
chizoba
via nutrient cycles and energy flows. For instance, the energy from the sun is captured by plants through photosynthesis. Photosynthesis is a biological process through which plants manufacture their own food with the aid of light from the sun and frc sources (e.g. cabon dioxide and water)
chizoba
What is cell wall
Taiwo Reply
cell wall is the outemost rigid covering of the plants ,that provides protection to the plants.
Aditi
what is ecology, ecosystem?
Nkeng Reply
what is digestive system
Lucky Reply
digestive system is the human syman system that icludes esopuges stomach o braking down of food in to useful substance to our body
samrawit
definition of biology basics
Ritu Reply
the potential energy of a molecule can be inquired by their number of?
Jesus Reply
what is the full meaning of RNA
Ayo Reply
ribose nucleic acid
Nikita
Ribonucleic acid
Jesus
Ribo Nucleic Acid
Aditi
ribonucleic acid
Nana
discuss, describe at least three (3) methods that could be used to improve photosynthesis..
Marvel Reply
Improve the efficiency with which plants capture light Improve the efficiency by which plants turn light into energy The smart canopy concept develop crop planting schemes that increase the penetration of sunlight into lower-level leaves.
Jesus
what is osmosis
Aon Reply
movement of water molecule from higher to lower concentration through a semipereable membrene.
Dr
what of in the case of solute
Aon
osmosis is the movement of molecules from higher concentration region to lower concentration region through semi-permeable membrane.
Broad
in case of solute means that water moves from the region with lower solutes to the region with higher solute. so it is vice versa to water.
Broad
osmosis is the movement of water molecule from a region of lower concentration to a region of higher concentration through a semi permeable membrane
Nana

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Source:  OpenStax, Concepts of biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11487/1.9
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