Biodiversity, Species Interactions, and Population Control Chapter 5

 How do species interact?  How can natural selection reduce competition between species?  What limits the growth of populations?  How do communities and ecosystems respond to changing environmental conditions?

Core Case Study: Southern Sea Otters: Are They Back from the Brink of Extinction?  Habitat  Hunted: early 1900s  Partial recovery  Why care about sea otters? Ethics Keystone species Tourism dollars

5-1 How Do Species Interact? 1) Species interact in 5 major ways a) Interspecific competition b) Predations c) parasitism d) Mutualism e) Commensalism 2) These interactions have significant effects on the resource use, population size & natural selection

2) Most species compete for resources a) Competition is the most common interaction b) Most competition involves the ability of 1 species to become more efficient than another at acquiring resources c) Competition occurs when niches overlap d) Competitive exclusion principle: no 2 species can occupy the exact niche e) We are taking over the habitats of many species

3) Most Consumer Species Feed on Live Organisms a) What is predation? b) How do carnivores catch prey? Pursuit, ambush, packs camouflage & chemical warfare c) How do prey avoid being caught? run, swim, fly, developed senses, protection, camouflage, chemical warfare, living in groups d) Warning coloration: the presence of bright colors to announce being dangerous or bad tasting e) Mimicry: Looks like dangerous or bad tasting organism

Predator and Prey Species Can Drive Each Other’s Evolution 4) Predators help remove, sick, weak, aged and least fit members 5) Predator-Prey put natural selection pressure on each other 6) Coevolution: 2 organisms evolve together due to their close relationship over a long period of time.

Science Focus: Why Should We Care about Kelp Forests?  Kelp forests: biologically diverse marine habitat  Major threats to kelp forests Sea urchins Pollution from water run-off Global warming

7) Some Species Feed off Other Species by Living on or in Them a) What is a parasite? b) Can be internal or external, promote species richness and regulate population

8) Mutualism a) What is mutualism? b) Gut inhabitant mutualism: bacterial live in the intestine and breakdown material, while receiving protection and nutrients

9) Commensalism a) What is commensalism? b) Epiphyte: live on branches of other plants to get to sunlight, water and nutrients

5-2 How Can Natural Selection Reduce Competition between Species? 1) Sharing resources: a) Resource partitioning: using shared resources in different ways

Some Species Evolve Ways to Share Resources b) Evolutionary Divergence: one species evolves into many to fill open niches

5-3 What Limits the Growth of Populations? 1) Population have certain characteristics a) distribution, numbers, age structure & density b) Population dynamics: study of how characteristics of populations change in response to environmental conditions 2) Distribution (dispersion): How organisms are arranged 3) Most common is clumping:

Fig. 5-12a, p. 112

advantages Tend to gather around available resources Better chance of encountering resources Protects some animals from predators Packs give predators a better chance of catching prey Temporary groups for mating and caring for young

Most Populations Live Together in Clumps or Patches (1) 4) Uniform and random groups

5) Populations Can Grow, Shrink, or Remain Stable a) Population size governed by births, deaths, immigration and emigration b) Population change = (births + immigration) – (deaths + emigration) c) Age structure: divides population into groups based on age divided into pre-reproductive, reproductive and post-reproductive groups d) The relative size of the pre-reproductive can give an idea of future population growth

6) No Population Can Grow Indefinitely: a) Biotic potential: capacity for population growth under ideal conditions b) Intrinsic rate of increase (r) growth rate with unlimited resources c) Those with high r: reproduce early and often, have short generation times, and have many offspring d) Environmental resistance: combination of all factors limiting the growth of a population. e) Carrying capacity (K): max. population that can be sustained indefinitely

Fig. 5-14, p. 115

7) J-Curves and S-Curves a) Exponential growth: starts slowly but accelerates quickly forms a J curve b) Logistic growth: starts rapidly, slows near carrying capacity and then levels off forms a S curve

Science Focus: Why Are Protected Sea Otters Making a Slow Comeback? Pg 110  Low biotic potential  Prey for orcas  Cat parasites  Thorny-headed worms  Toxic algae blooms  PCBs and other toxins  Oil spills

8) When a Population Exceeds Its Habitat’s a) Overshoot b) Reproductive time lag: period of time for birth rate to fall & death rate to rise c) Die Back or crash: d) Carrying capacity is not fixed e) Overshoots can sometimes cause the carrying capacity to be lower

Fig. 5-17, p. 116

9) Species Have Different Reproductive Patterns a) r-selected: have a high rate of population growth, usually with many, small offspring and provide little protection b) Opportunistic: grow rapidly under certain conditions c) K-selected: Slow population growth, usually few, large offspring and provide longer periods of protection d) Tend to do well in a stable ecosystem e) Most organisms are in the middle

10) Genetic Diversity Can Affect Small Populations a) A few individuals colonize a habitat resulting in little diversity b) Bottleneck: only a few individuals in a population survive a catastrophe resulting in little diversity c) Genetic drift: small populations can have a random shift in gene frequency d) Inbreeding: increases the frequency of defective genes leading to increase in genetic disorders e) Minimum viable population size: number of individuals needed for long-term survival of a species

11) Population Density Affects Population Size a) Density dependent controls: predation, parasitism, infectious disease and competition b) Density independent: controls not related to density (fires, freeze, clear cut forest) 12) Types of population change a) Stable b) irruptive c) cyclic (boom-bust) (top down or bottom up?) d) irregular

Fig. 5-18, p. 118

13) Humans Are Not Exempt a) Ireland: Potato crop in 1845 b) Bubonic plague: Fourteenth century c) AIDS: Global epidemic d) What is our carrying capacity & when will we reach it?

Case Study: Exploding White-Tailed Deer Population in the U.S.  1900: deer habitat destruction and uncontrolled hunting  1920s–1930s: laws to protect the deer  Current population explosion for deer Lyme disease Deer-vehicle accidents Eating garden plants and shrubs  Ways to control the deer population

5-4 How Do Communities and Ecosystems Respond to Changing Environmental Conditions? 1) Ecological Succession: a) Gradual change in species composition in a given area b) Primary: Begins without soil for terrestrial or bottom sediment in aquatic systems c) Secondary: Begins with soil/bottom sediment after ecosystem destruction

Fig. 5-19, p. 119

Fig. 5-20, p. 120

Science Focus: How Do Species Replace One Another in Ecological Succession?  Facilitation  Inhibition  Tolerance

2) Succession Doesn’t Follow a predictable Path a) Traditional view: Balance of nature and a climax community b) Current view 1. Succession is the result of ongoing struggle to survive 2. Mature late-successional ecosystems are in a s tate of continual disturbance and change 3. Ever-changing mosaic of patches of vegetation

3) Living Systems Are Sustained through Constant Change a) Inertia, persistence: Ability of a living system to survive moderate disturbances b) Resilience: Ability of a living system to be restored through secondary succession after a moderate disturbance c) Evidence suggest ecosystems have one or the other, but not both d) Tipping point: point where additional stress causes an abrupt and irreversible change.