Chapter 5:

Core Case Study: The Southern Sea Otter: A Species In Recovery Southern Sea Otters live in giant kelp forests in shallow waters along part of the pacific coast of North America. It is believed that between 16,000 and 17,000 Sea Otters once lived in the waters of their habitat area along Californian Coast.

By the early 1900’s, the species was hunted almost to extinction. Biologists have marked Otters as a Keystone species as it triggers the health of the community around it, and it supports other various organisms within its niche.

5.1- How Do Specimens Interact? Mutualism: Relationship in which both organisms receive a benefit from interaction. Commensalism: Relationship when one organism benefits and causes little or no harm to the other. Interspecific competition: when members of 2 or more species interact to gain access to limited resources. Predation: When a predator feeds directly on all or part of a member of another species. Parasitism: When one organism(parasite) feeds of another(host) usually by living on the host.

Most Species Compete With One Another For Certain Resources While fighting for resources, most competition involves the ability of one species to become more efficient that others in getting food, space, light etc. When niches overlap, the more intense competition becomes.

Some Species Evolve In Ways To Some Resources Resource partitioning occurs when species competing for similar scarce resources by using them in different ways. Adaptations allow species to reduce competition by feeding in different portions of certain trees or animals.

Most Consumer Species Feed On Live Organisms of Other Species Predators have various measures to capture carnivores. For example: pursuit and ambush, camouflage, chemical warfare, behavior strategist , mimicry, and warning coloration.

Science Focus A kelp forest is composed of large concentrations of a seaweed called giant kelp whose long blades grow straight to the surface. Sea urchins and pollutions are major threats to kelp forests. Other threats to kelp forests include polluted water runoff and warming waters.

5.1- Interactions between Predator and Prey Species Can Drive Each Other’s Evolution Coevolution describes process in which populations of 2 different species interact & cause a change in the gene pool which leads to a change in the others gene pool helping competition. Bats & Moth: Bats hunt at night using echolocation to navigate and locate prey. To counteract this, some moths have developed ears sensitive to the frequencies emitted by bats.

Some Species Feed Off Other Species By Living On Or Inside Them Some parasites such as tapeworms live inside their hosts. Sea Lampreys attach themselves to the outside quarters of their host fish and absorb their nutrients to survive. The parasite thrives off the host entirely until they suck the host dry.

In Some Interactions, Species Benefit Mutualism Interaction in which both species receive a benefit. Examples include birds that ride on the backs of large rhinos, buffalo, and elephants. Birds remove parasites and pests from animals body and often make noises to warm when larger predators are approaching.

In Some Interactions, Once Species Benefits and The Other Is Not Harmed Commensalism An interaction in which one species benefits while the other is left with no gain or loss and is unharmed. Examples include Epiphytes. Smaller air plants attach themselves to larger plants giving themselves access to sunlight, water, an humid air while no effect left on mothering tree.

5.2- What Limits The Growth of Populations? No population can continue to grow indefinitely because of limitations on resources and because of competition among species for those resources.

Most Populations Live In Clumps A population is a group of interbreeding individuals of the same species. Members of a population are typically distributed in three different ways: Clumped, Uniform, Random. Most Populations live together in clumps such as packs of wolves, school of fish, and flocks of birds.

Populations Can Grow, Shrink, or Remain The Same 4 Variables: Births, deaths, immigration, emigration. Pop change= (Births+ Immigration) – ( Deaths+ Emigration. Populations age structure: Its distribution of individuals among various age groups- can have a strong effect on how rapidly it can increase/decrease. Predation Age: Not mature enough to reproduce. Reproductive Age: Capable of reproduction efficiently. Past- Reproductive Age: Organisms to old to reproduce.

Some Factors Can Limit Population Size Each population in an ecosystem has a range of limits to its physical and chemical environment. Often, one or more limits, AKA Limiting Factors, are most important than factors in equation of population growth. Limiting Factor Principle: too much or too little of any physical or chemical factor can limit or prevent growth of populations.

No Population Can Grow Indefinitely: S- Curve & J- Curve Environmental Resistance is the combination of all factors that act to limit population growth. Carrying Capacity: Max. population of a given species that a particular habitat can support indefinitely. Exponential Growth grows slowly as population increases, because base size of population is increasing.

Explaining White-Tailed Deer Population In U.S. By 1900, habitat destruction and urban expansion reduced the white-tailed deer population in the U.S to about 500,000. In the 1920’s and 30’s, laws were passed to protect and preserve the deer. These procedures worked successful, perhaps too well. Today there are 25 Million white-tailed deer in U.S.

5.3- How Do Communities and Ecosystems Respond to Changing Environmental Conditions? The structure and species composition of communities and ecosystems change in response to changing environmental conditions through a process called ecological succession.

Communities and Ecosystems Change over Time: Ecological Succession The normally gradual change in species composition in a given area is ecological succession. Primary ecological succession involves the gradual establishment of biotic communities in lifeless areas where there is no soil or sediment. Secondary ecological succession occurs when a series of communities or ecosystems with different species develop in places containing soil or sediment.

Succession Does Not Follow a Predictable Path A climax community is dominated by a few long-lived plant species and is in balance with its environment. This equilibrium model of succession is what ecologists once meant when they talked about the balance of nature. The current view is that we cannot predict a given course of succession ore view it as inevitable progress toward an ideally adapted climax plant community or ecosystem. Rather, succession reflects the ongoing struggle by different species.

Living Systems Are Sustained through Constant Change All living systems are constantly changing in response to changing environmental conditions. There are two aspects of stability in living systems: -inertia/persistence: the ability of a living system to survive moderate disturbances. -resilience: the ability of a living system to be restored through secondary succession after a more severe disturbance.

Chapter 5’s Big Ideas Certain interactions among species affect their use of resources and their population sizes. There are always limits to population growth in nature, Changes in environmental conditions cause communities and ecosystems to gradually alter their species composition and population sizes (ecological succession).