Transcript BODY SIZE
BODY SIZE Basic conditions for life 8. Non-eccentric orbits to avoid collisions 1. Source of constant and stable energy 7. Carbon and oxygen 2. A terrestrial planet 4. Need a satellite star 5. Near circular orbit 6. The right place in the galaxy A basic principle: Energy BIOMAS SPECIES Body size Number of species Abundance Ecological / Evolutionary forces Why a species has the body size it does? Optimum trade-off Cost Benefit Body size Evolutionary forces: source availability Large individuals use ↑ Resources Small individuals use ↓ Resources Environment’s role Resource available ↓ Resulting body size ↘ Resource available ↑ Resulting body size ↗ Evolutionary forces: source availability evidence 41,000 y BP 12,000 y BP Extinct 9,500 y BP Individuals 25% smaller were found in a small island Fossils dated 7,000–4,000 yr BP No humans Russia Alaska No glaciation Dwarfing most likely due to limited resources Vartanyan et al., Nature 1993 Evolutionary forces: ecological forces PREDATION PREY Expected size PREDATOR Smaller is better Bigger is better Evolutionary forces: ecological forces Distribution of organisms Competition Time Time Resource variation By specializing, species use a smaller spectrum of available resources… so they have to compromise either their size or their abundance Evolutionary forces: ecological forces Competition: Soule 1966 classic work Smaller is better… …or rather smaller is forced Types of competition: by interference & by exploitation BY INTERFERENCE: one species prevent other species of accessing a limiting resource. Example: Territorial damselfishes competing for benthic algae How will body size change over time under this type of competition among species? Competition BY EXPLOITATION: two o more species have free access to a limiting resource and variation among species in competitive abilities will determine variations in species performance: eg. growth, reproduction. Such sort of competition is common among species that compete for resources that are not defensible spatially. Example: Damselfishes of the genus Chromis competing for plankton How will body size change over time under this type of competition among species? Evolutionary forces: ecological forces Competition and the Taxon Cycle (E. O. Wilson 1961) Abundance Body size Evolutionary forces: climate Clarke & Jonhston, J. Ani.Ecol. 1999 Energy required to maintain metabolisms increase with increasing temperature In laboratory experiments, for every 2 degrees the scientists cranked up the temperature, various types of fruit flies decreased anywhere from 3 to 17 percent. For fish, the shrinking was even more pronounced, from 6 to 22 percent A male frog specimen from Mount Kinabalu in Malaysia 1980s 2008 Everything else being equal Body size should reduce with increasing temperature Sheridan & Bickford, Nature Climate Change 2011 Evolutionary forces: hunting 40,000 years Wallaroo Tasmanian devil Koala Flannery Book 1994 Nothing explains this reduction in body size better than the fact that humans colonized the islands some 40,000 years ago and that humans liked bigger animals Selection on the fittest Evolutionary forces: fishing 1957 1980 2007 MacClanaham Conservation Biology 2009 Jackson et al, Science 2001 Geographical variations in body size: Bergmann's rule Body size increases with colder temperatures 2 2 Mass=8 Area=24 Area/Mass=3 A lower area/mass ratio helps to conserve heat which is very adaptable in cool temperature 2 Roberts DF (1978) Climate and human variability 1 1 1 Mass=1 Area=6 Area/Mass=6 A higher area/mass ratio helps to dissipate heat which is very adaptable in warm temperature Geographical variations in body size: Allen's rule Limbs and other appendices are shorter and more compact in individuals living in colder temperatures The greater the exposed surface area, the greater the loss of heat and therefore energy Mass=8 Area=24 Area/Mass=3 Will conserve more heat, which is better in colder environments Mass=8 Area=28 Area/Mass=3.5 Will dissipate more heat, which is better in warmer environments Geographical variations in body size: Cope's rule Lineages tend to increase in body size over evolutionary time Size benefits survival, mating success and fecundity (Hone & Benton, Trends Ecol. Evol. 2005) Geographical variations in body size: Island rule Insular body size of terrestrial mammal as percentage of body size of the species on the mainland (Sm) Small species get larger Ecological release Large species get smaller Resource limitation Why shall we care about patterns in body size? Because body size influences the risk of becoming extinct Forero et al., Biota Neotrop 2009 Why is this important Mammalian body mass by current extinction risk Davidson A D et al. PNAS 2009;106:10702-10705 Why is this important Rapid body size decline in Alaskan Pleistocene horses before extinction Guthrie, Nature 2009 Current declines in body size are worrisome sings of extinction In summary Resources Interactions: predation, competition Determinants Climate Human driven evolution Body size Bergmann's rule: Body increase with latitude Patterns Allen's rule: Limbs and other appendices get shorter in colder areas Cope's rule: Body increase with evolutionary time Island rule: On islands large species get smaller and vice versa