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Population Growth Curves
Exponential vs. Logistic Growth
Predator-Prey Population Cycles
Fig. 38.4
Figures 38.3
and 38.5
What do Ecologists Study?
• Ecosystem: all interactions between living things
(community) and physical factors in a given area
– Biotic (living) vs. abiotic (non-living) factors (ex., floods, droughts)
• Habitat: place where organism lives; can be general or
specific (biomes are major climatic zones)
• Niche: organism’s way of life; multi-dimensional; in theory,
only one species can occupy a niche (ecological
species concept)
• Energy Flow: producers, autotrophs, phytoplankton;
consumers, heterotrophs, zooplankton, herbivores,
carnivores, omnivores, detritivores, decomposers
– Food Chains: ~90% energy loss each trophic step
– Food Webs: more realistic; note importance of krill in Southern
Ocean food web (shared resource, not necessarily limited)
– Food Pyramids: less biomass (and abundance) at higher levels;
decomposers act on all trophic levels
• Biogeochemical Cycles: hydrologic, carbon, nitrogen cycles
– Carbon cycle: related to global warming theory
Fig. 37.4
Fig. 38.1
Fig. 38.13
Fig. 38.14
Fig. 38.15
What Relationships Exist Between
Organisms in Ecosystems?
• Predation and Anti-predation
– Diet Specialists/Generalists: specialists can have morphological, behavioral,
and physiological adaptations for capturing/assimilating prey; scarcity of
prey can lead to extinction of diet specialists
– Anti-predation: cryptic and warning colorations, mobbing, displays
• Competition: assumes a limited (not just shared) resource; removal
experiments used to test for effects on fitness
– Intraspecific: between members of same species; most intense is between
males for access to females
– Interspecific: between separate species; can lead to competitive exclusion
– Scramble: rare in nature; all may get less than needed
– Contest: mechanisms; ex. harems vs. sneakers (ex., wrasse, marine iguana)
• Symbiosis: evolved life-relationship between two or more species
– Mutualism: both species benefit (ex. anemone and clownfish)
– Parasitism: one benefits, other is harmed; endo- and ectoparasites
– Commensalism: one benefits, other with no effect; least common,
examples often debated (exs. whale shark with pilotfish; reef shark with
remora? – debatable, since remora may cause hydrodynamic drag)
• Facilitation: organism indirectly benefits others (ex., earthworms aerate
soil, nightly excretion of ammonium by blacksmith benefits algae)
Fig. 38.10
Why is Biodiversity Important?
• Biodiversity: variation among living organisms
– Species diversity: number of species in an ecosystem; increases
with stability/uninterrupted evolution (ex., deep sea, tropical rain
forests), and available niches; decreases with isolation
– Genetic diversity: variation within a species
• If low, more vulnerable to catastrophic changes/extinction
• Importance of Biodiversity
– Ecosystem stability: keystone species are those with influence
disproportionate to their abundance (ex. sea otter in Alaska)
– Genetic reserves; esp. regarding agriculture; endemic species are
unique to particular habitat (ex. marine iguana in Galapagos Is.)
– Practical uses (ex. medicine, future foods)
– Aesthetic and ethical value: biophilia, Gaia Hypothesis
• Largest Threats to Biodiversity
1. Habitat loss and fragmentation: conservation incl. wildlife corridors
2. Introduced species (especially on islands)
3. Hunting/poaching; illegal trade  international treaty (CITES)
Fig. 38.12
Endemic Species