Biodiversity, Species Interactions, and Population Control Chapter 5

Case Study- Southern Sea Otter Why is the sea otter considered a keystone species?

HOW DO SPECIES INTERACT? Section 5-1

Most species compete with one another for certain resources There are five basic types of interaction between species when they share limited resources: –Interspecific competition occurs when two or more species interact to gain access to the same limited resources. –Predation occurs when a member of one species (predator) feeds directly on all or part of a member of another species (prey). Symbiosis= close, long term association 2 or more species: 3 types –Parasitism + - occurs when one organism (the parasite) feeds on another organism (the host), usually by living on or in the host. –Mutualism + + is an interaction that benefits both species by providing each with food, shelter, or some other resource. –Commensalism + 0 is an interaction that benefits one species but has little, if any, effect on the other.

Interspecific Competition Interspecific competition is the most common interaction between species. When two species use the same resource, their niches overlap. Resource partitioning occurs when species competing for similar scarce resources evolve specialized traits that allow them to use shared resources at different times, in different ways, or in different places. –e.g. warblers who live in the same trees but have such specialized feeding niches that they do not compete.

Sharing the wealth

Predation Predation occurs when a member of one species (predator) feeds directly on all or part of a living organism of another plant or animal species (prey), forming a predator-prey relationship.

Avoiding and Defending Against Predators  Escape  Senses  Armor  Camouflage  Chemical warfare  Warning coloration  Mimicry  Behavior strategies  Safety in numbers

Span worm Bombardier beetle Viceroy butterfly mimics monarch butterfly Foul-tasting monarch butterfly Poison dart frog When touched, the snake caterpillar changes shape to look like the head of a snake Wandering leaf insect Hind wings of io moth resemble eyes of a much larger animal Fig. 6-6, p. 116 How Species Avoid Predators “If it is small and strikingly beautiful, it is probably poisonous. If it is strikingly beautiful and easy to catch, it is probably deadly.” - E.O Wilson camouflage Chemical warfare / Warning mimicry Deceptive behavior

Coevolution occurs when two different species interact over a long period of time and changes in the gene pool of one species can lead to changes in the gene pool of the other. Some bats and moths have coevolved.

Parasites  Parasitism + -  Hosts  Inside or outside of hosts  Harmful effects on hosts  Important ecological roles of parasites

Parasitism

Mutualism + +  Both species benefit  Pollination  Benefits include nutrition and protection  Mycorrhizae - fungi that helps plants extract nutrients and water from soil  Gut inhabitant mutualism

Oxpeckers and black rhinocerosClown fish and sea anemone Lack of mycorrhizae fungi on juniper seedlings in sterilized soil Fig. 6-7, p. 117 Examples of Mutualism © 2006 Brooks/Cole - Thomson Mycorrhizae fungi on juniper seedlings in normal soil

Commensalism + 0  Species interaction that benefits one and has little or no effect on the other  Example: Small plants growing in shade of larger plants  Epiphytes  Forehead mites

Example of commensalism

WHAT LIMITS THE GROWTH OF POPULATIONS? Section 5-2

Population Dynamics: Factors Affecting Population Size  Population change = (births + immigration) – (deaths + emigration)  Age structure (stages)  Age and population stability

Limits on Population Growth  Biotic potential (capacity for growth)  Intrinsic rate of increase (r) (assumes unlimited resources)  No indefinite population growth  Environmental resistance = all the factors that limit population growth  Carrying capacity (K) - determined by biotic potential & enviro resistance

Fig. 6-11, p. 121 Carrying capacity (K) Environmental resistance Biotic potential Exponential growth Population Growth Curves Time (t) Population size (N)

Species have different reproductive patterns Some species have many, usually small, offspring and give them little or no parental care or protection. Some species have few, usually fairly large, offspring and invest parental care and protection.

Reproductive Patterns  r-selected species  Opportunists (mostly r-selected)  Environmental impacts on opportunists  K-selected species (competitors)  Intermediate and variable reproductive patterns

Fig. 6-15, p. 123 r-selected Opportunists and K-selected Species

Exponential and Logistic Population Growth  Resources control population growth  Exponential growth - J-shaped curve  Logistic growth - S-shaped curve

No population can continue to grow indefinitely

When Population Size Exceeds Carrying Capacity  Switch to new resources, move or die  Overshoots  Reproductive time lag  Population dieback or crash  Human Famines - Irish potato famine million dead  Factors controlling human carrying capacity- technology has increased carrying capacity for humans

Exponential growth, overshoot, and population crash of reindeer introduced onto St. Paul.

HOW DO COMMUNITIES AND ECOSYSTEMS RESPOND TO CHANGING ENVIRONMENTAL CONDITIONS? Section 5-3

Ecological Succession: Communities in Transition  What is ecological succession? (Gradual change in species composition)  Primary succession = establishment of communities on nearly lifeless ground (no soil) ex. glacier retreat, landslide, lava, abandoned parking lot  Secondary succession - community disturbed, soil remains. Burned / cut forests, polluted stream, flood

Primary ecological succession

Two types of ecological succession animation. Animation ller/animations/ch05/animation_media/succession/succession.html

Communities and ecosystems change over time: Ecological succession Secondary succession occurs with a series of communities or ecosystems with different species develop in places containing soil or bottom sediment. Such areas include: –Abandoned farmland. –Burned or cut forests. –Heavily polluted streams. –Flooded land.

How Predictable is Succession?  Climax community concept - orderly sequence-  “Balance of nature”- old school  New views of equilibrium in nature -  Unpredictable succession - “The modern view is that we cannot project the course of a given succession….”  Natural struggles

Natural ecological restoration of disturbed land

Living systems are sustained through constant change Living systems contain complex processes that interact to provide some degree of stability. This capacity to withstand external stress and disturbance is maintained by change in response to changing environmental conditions. One aspect of stability is inertia, or persistence, which is the ability of a living system, such as a grassland or forest, to survive moderate disturbances. A second aspect of stability is resilience, which is the ability of a living system to be restored through secondary succession after a more severe disturbance.

Three big ideas Certain interactions among species affect their use of resources and their population sizes. There are always limits to populations growth in nature. Changes in environmental conditions cause communities and ecosystems to gradually alter their species composition and population sizes (ecological succession).