Population Growth Curves

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 speciesconcept) • 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

Population Growth Curves