Terres. Ecol. - 1

Question of the Day Which statement below is NOT CORRECT describing zebra mussels? A. zebra mussels are filter feeders that clear water in the Great Lakes B.zebra mussels are native to the Great Lakes, having been transported to other locations by clinging to boat hulls C.zebra mussels were brought here from commercial vessels that came from the Black Sea transpiration D.zebra mussels block commercial and civic inlet and outlet pipes in lakes and rivers

Terrestrial Ecology Notes

“The Tragedy of the Commons” In his essay, ecologist Garrett Hardin argued that the main difficulty in solving environmental problems is the conflict between the short-term interests of the individual versus the long-term welfare of society. The example he used was the commons, or the areas of land that belonged to the whole village.

Tragedy of the Commons A common-property resource, which are owned by no one but are available to all users free of charge. Most are potentially renewable. Ex. Clean air, open ocean and its fish, migratory birds, Antarctica, the ozone, and space.

“The Tragedy of the Commons” It was in the best interest of the individual to put as many animals in the commons as possible. However, if too many animals grazed on the commons, they destroyed the grass. Once the grass was destroyed, everyone suffered because no one could raise animals on the commons.

“The Tragedy of the Commons” The commons were eventually replaced by closed fields owned by individuals. Owners were now careful not to put too many animals on their land, because overgrazing wouldn’t allow them to raise as many animals next year. Hardin’s point being that someone or some group must take responsibility for maintaining a resource or it will become depleted.

The Tragedy of the Commons

THE NATURE OF ECOLOGY Ecology is a study of connections in nature. – How organisms interact with one another and with their nonliving environment. Figure 3-2

Species Interactions Species interactions are the backbone of communities Most important categories – Competition = both species are harmed – Predation, parasitism, and herbivory = one species benefits and the other is harmed – Mutualism = both species benefit – Commensalism = one benefits, other has no afffect

Competition Competition = relationship where multiple organisms seek the same limited resources they need to survive: – Food - Water – Space - Shelter – Mates - Sunlight Intraspecific competition = between members of the same species – High population density = increased competition Interspecific competition = between members of 2 or more species – Leads to competitive exclusion or species coexistence

Interspecific Competition Competitive exclusion = one species completely excludes another species from using the resource Species coexistence (Niche Restriction) = neither species fully excludes the other from resources, so both live side by side – This produces a stable point of equilibrium, with stable population sizes – Species adjust to minimize competition by using only a part of the available resource

Predator An organisms that captures & feeds on parts or all of another animal.

Predation Exploitation = one member exploits another for its own gain – Predation, parasitism, herbivory Predation = process by which individuals of one species (predators) capture, kill, and consume individuals of another species (prey) – Structures food webs – Influences community composition through number of predators and prey

Importance in Population Control Predators usually kill the sick, weak or aged. This helps to let the rest of the prey have greater access to the available food supply. It also improves the genetic stock.

Prey An organisms that is captured & serves as a source of food for another animal.

Effects of predation on populations Increased prey populations increases predators – Predators survive and reproduce Increased predator populations decrease prey Decreased prey population causes starvation of predators Decreased predator populations increases prey populations

Importance of Predators

Predator/Prey Cycles

Herbivory Exploitation in which animals feed on the tissues of plants – Widely seen in insects – May not kill the plant, but affects its growth and survival Defenses against herbivory include – Chemicals: toxic or distasteful parts – Physical: thorns, spines, or irritating hairs – Other animals: protect the plant

SPECIES INTERACTIONS: COMPETITION AND PREDATION Species can interact through competition, predation, parasitism, mutualism, and commensalism. Some species evolve adaptations that allow them to reduce or avoid competition for resources with other species (resource partitioning).

Symbiosis Parasitism –when 1 species (parasite) feeds on part of another species (host) by living on or in it for a large portion of host's life. Commensalism – benefits one species but doesn't harm or help the other Mutualism – both species benefit

Parasites: Sponging Off of Others Although parasites can harm their hosts, they can promote community biodiversity. – Some parasites live in host (micororganisms, tapeworms). – Some parasites live outside host (fleas, ticks, mistletoe plants, sea lampreys). – Some have little contact with host (dump-nesting birds like cowbirds, some duck species)

Mutualism: Win-Win Relationship Two species can interact in ways that benefit both of them. Figure 7-9

Fig. 7-9a, p. 154 (a) Oxpeckers and black rhinoceros

Commensalism: Using without Harming Some species interact in a way that helps one species but has little or no effect on the other. Figure 7-10

Relationships with no effect on one member Amensalism = a relationship in which one organism is harmed while the other is unaffected – Difficult to confirm, because usually one organism benefits from harming another – Allelopathy = certain plants release harmful chemicals – Or, is this competition? Commensalism = a relationship in which one organism benefits, while the other remains unaffected – Facilitation = plants that create shade and leaf litter allow seedlings to grow

Community Interactions Sn4&feature=share&list=PL7WxmjMiAYikN GKPUWeZxBNOhKsd8LxSo Sn4&feature=share&list=PL7WxmjMiAYikN GKPUWeZxBNOhKsd8LxSo

Question of the Day Which statement below best describes the role of predators in ecosystems? A. predators only take herbivores that are weakened by inheritance, injury, disease or old age. B. predators dominate an ecosystem because they get more energy than the herbivores predators with large teeth and claws or beaks and talons typically outnumber and outweigh the less aggressive herbivores C. Predators always have a larger body than their herbivores prey D. predators serve an ecosystem by reducing the size of populations of herbivores to their environmental carrying capacity