D. Adaptive Radiation

Transcription

1 D. Adaptive Radiation One species new species: A new species: B new species: C new species: D Typically occurs when populations of a single species... invade a variety of new habitats, evolve under different environmental pressures (selective forces) Examples: Darwin s Galapagos Finches, Hawaiian Silverswords 1

2 IV. Pace of Evolution Gradualism phenotypic change Evolutionary change is slow and imperceptible from generation to generation Over the course of thousands and millions of years, major changes could occur Punctuated equilibrium Evolution normally proceeds in spurts, with long periods of little evolutionary change in between. The proposed stasis would be expected in large populations experiencing stabilizing selection over long periods of time. V. Extinction Extinction = death of all the members of a species How and why does it happen? (1) Localized distributions & overspecialization Increase an organism s likelihood of extinction Devil s Hole pupfish: Lives in isolated water pools in Mojave Desert 2

3 What Causes Extinction? (2) Interactions with other organisms - competition, parasitism, predation EX. the Panama land bridge: connected 2 continents, formed during the Pleiocene (~3 mya) N. American species & South American species mixed! For the first time in history Many S. American species were out-competed! went extinct Habitat change / destruction What Causes Extinction? 3

4 Speciation and Extinction Through Time There have been 5 major mass extinctions interspersed within relatively consistent extinction patterns. most famous! end of Cretaceous period (65 mya); dinosaurs went extinct Mammals quickly experienced evolutionary radiation. Biological diversity tends to rebound after mass extinctions What Causes Extinction? (3) habitat change / destruction What can we do? BOZEMAN PASS WILDLIFE LINKAGE 4

5 Ecology I. Definitions II. Population Ecology III. Community Ecology IV. Ecosystem Ecology An ecosystem consists of all the organisms living in a community as well as all the abiotic factors with which they interact Microcosm to lakes to forests, etc. Biosphere as global ecosystem made up of all the local ecosystems on Earth Ecological Hierarchy 5

6 Chemicals cycle within ecosystems Two major processes occur w/i ecosystems: I. Energy enters (sun) and is fixed within the system. This energy can be transferred b/n organisms or converted to heat. II. Chemical elements move through ecosystems in biogeochemical cycles. Water Cycle! All life depends on water! Only ~2% of the Earth s water is captured in any form!all of the rest is free water! 96% of all fresh water in the US is groundwater Carbon cycle! CO 2 makes up ~0.03% of our atmosphere, much more in our oceans! Photosynthetic bacteria, protists, & plants fix CO 2! Essentially all heterotrophic organisms obtain their carbon either directly or indirectly from photosynthetic organisms! Increasing amounts of carbon dioxide in our atmosphere appear to be a major player in Global Climate Change (aka Global Warming) 6

7 Nitrogen cycle! Nitrogen is an essential component of organic compounds such as proteins and amino acids! The atmosphere is ~78% N 2 (N N)! Certain prokaryotes can fix nitrogen from the atomosphere Root nodules Energy flows through ecosystems! An ecosystem includes both autotrophs and heterotrophs! Autotrophs are the primary producers Much of the energy that passes through ecosystems is converted to heat Trophic levels within a food chain 7

8 Food chains!b/c considerable energy is converted to heat at each stage, the length of food chains is limited! Food chains generally consist of 3 or 4 steps Smelt Biogeographic patterns of species diversity! The tropics contain the greatest amount of biodiversity! The reasons for this include higher productivity, climatic predictability, increased predation, and spatial heterogeneity Bird diversity 8

9 Ecosystem change over time Mature ecosystems are complex networks. Emerge in very slow stages. Begins with disturbance e.g. fire, landslide Succession: Structural change in ecosystem over time. Two main types 1. Primary succession 2. Secondary succession 1) Primary succession: from scratch 1) Bare Rock! Weathering 2) Pioneer species: lichens, mosses 3) start the soil creation process, in conjunction w/ prokaryotes 4) Then herbs shrubs animals 5) Eventually: Mature ecosystem 9

10 2) Secondary succession Occurs after an established ecosystem is disturbed! Fire! Abandoned farm fields! Already soil, seed bank! In the case of fire, it is very patchy! Faster than primary succession ( 200 yrs) Will eventually recover to a mature ecosystem. Secondary succession & disturbance Some ecosystems undergo regular disturbance: In this case, all organisms have evolved to live under these conditions (e.g. fire adapted ecosystems)! Can promote diversity 10

11 Secondary succession Pristine lowland rainforest in Eastern Borneo dominated by trees of the dipterocarp family. Secondary succession Initial surface fire in the same forest, which has been selectively cut since

12 Secondary succession Three years after the initial fire. Most trees are killed by the surface fire, some by drought stress, but some trees are still standing. Secondary succession Thirteen years after the initial fire. More standing trees have died and collapsed. The undergrowth is dominated by pioneer tree species (predominantly Macaranga spp.). This secondary succession becomes highly flammable in extremely dry years. 12

13 Secondary succession A second fire. The tree layer, including the postfire secondary succession, is almost completely killed by a high-intensity fire. Secondary succession Final stage of fireinduced savannization of the rainforest in a nearby site. The area is dominated by an aggressive invading grass species (Imperata cylindrica) 13

14 Secondary succession Biomes Major ecosystems that cover broad geographical regions What determines the type of biome? Broadscale climatic conditions interacting with other abiotic factors: Climate: Rainfall, elevation, temperature Abiotic factors: Soils, nutrient availability 14

15 Major terrestrial biomes 30ºN Tropic of Cancer Equator Tropic of Capricorn 30ºS Tropical forest Savanna Desert Chaparral Temperate grassland Temperate broadleaf forest Coniferous forest Tundra High mountains Polar ice The Onion 15

16 !"#$%&'(')*$+, - 16