Transcript PPT
Fig - Fig Wasp Natural History 750 spp. of fig, most with a single sp. of pollinator!! http://129.31.3.171/index.html Fig - Fig Wasp Model MVP: ~ 170 fig trees are required to eliminate a gap in flowering among trees - i.e., 99% probability of persistence for 1000 years. Big-Blue Butterfly An obligate parasite of ant colonies Butterfly oviposits on thyme Caterpillar becomes a beautiful butterfly Caterpillar is fed by / feeds on ants http://faculty.plattsburgh.edu/thomas.wolosz/metapop.htm Caterpillar feeds on thyme Caterpillar enters Myrmica ant nest Big-Blue Butterfly • First started disappearing in the 19th century • Hypotheses – – – – – Over-collecting by insect collectors Insecticides Fragmentation Climate change Air pollution • Rapid decline in the 1950’s, extinct by 1979. Big-Blue Butterfly BUTTERFLY THYME SHORT GRASSY FIELDS ANT COLONY (Myrmica sabuleti) GRAZING MYXOMATOSIS RABBITS Migratory Birds • Studies have identified a decrease in U.S. neotropical migrants – Decreasing at the rate of 0.5 to 1.0% per year • Hypotheses – Deforestation in tropics or breeding ground – Susceptibility to predation or cowbird parasitism on breeding grounds Brown-headed cowbird The Evidence • Based on taxonomically diverse community in eastern U.S. – Decline of migrants equal to ~ 1% / year. • Based on wood warblers, vireos, gnatcatchers, kinglets, titmice, chickadees, nuthatches, brown creeper, wrens, bluebirds across U.S. – No decline for migrants – Recent declines in birds with high susceptibility to predation / cowbird parasitism Black-Footed Ferret The most endangered mammal in N. America http://www.ngpc.state.ne.us/wildlife/ferret.html Inter-relationship of species “The number of bumblebees in any district depends in a great measure upon the number of field-mice, which destroy their combs and nests”. “[Because] the number of mice is largely dependent, as everyone knows, on the number of cats . . . It is quite credible that the presence of a feline animal in large numbers in a district might determine, through the intervention first of mice and then of bees, the frequency of certain flowers in that district!” - Charles Darwin, On the Origin of Species Keystone Species Photo by James M. Cook Keystone Species Species with a disproportionate effect on community structure. Keystones Dominants Total Effect strong interactors Common Cold weak interactors Abundance From: Meffe and Carroll Problems with the Keystone Species Concept • • • • Loosely applied Difficult to test Questionable application Conclusion: Focus on interaction strengths Ecological Niche abundance • Grinnell (1917): where a species lives (habitat) • Elton (1927): what a species does • Hutchinson (1950s): combination of all biotic and abiotic requirements of a species: n-dimensional “hyper-volume” seed size temperature predator density Competitive Exclusion abundance abundance • If the niches of two competing species overlap by “too much”, then one tends to replace the other. • Corollary: Competition drives the evolution of divergent niches or life-history strategies (i.e., respond or perish) niche niche Darwin’s Finches: Character Displacement “The Ghost of Competition / Predation Past” • What we see today may be the result of competition / predation in the past (i.e., implies evolutionary history). – Consider Pleistocene extinctions • Conservation Implication: Exotic species may have their most negative effects after invading communities that lack an analogous evolutionary partner