lecture note 23 for BGYB50

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Department
Biological Sciences
Course
BIOC50H3
Professor
Herbert Kronzucker
Semester
Winter

Description
LECTURE 23/24: - Unlike competition or predation, mutualism is a species-species interaction where both species benefit from the interaction - Important examples include: squids and Vibrio bacteria (bacteria are attracted to live inside a specialized “light organ” of the squids, protecting the bacteria from predation, and giving the squid the ability to change colour on account of the bacteria’s ability to produce bioluminescence); N-fixation symbioses; mycorrhizae (the close physical association between fungi and the roots of plants; the fungal partner enhances the nutrient acquisition capacity of the plant, esp. for phosphorus and nitrogen, while the plant supplies the fungus with carbohydrates; 80% of higher plant species are mycorrhizal, not just trees), lichens (composite organisms consisting of a fungus, known as the mycobiont, and an alga or cyanobacterium, known as the phycobiont; the mycobiont is very efficient at obtaining nutrient ions from the environment, while the phycobiont supplies photosynthate; lichens are critical components of primary succession, where they aid in the weathering of rocks and the production of soil), or intestinal bacteria (e.g. bacteria in the guts of termites enable termites to digest lignin from woody substrate; humans also have numerous symbiotic gut bacteria that aid in the digestion process; all these bacteria get shelter and nutrients from the “host” in return) - Mutualisms can also be non-symbiotic (such as between hummingbirds and the flowers they feast on), and may be either obligatory (i.e. the mutualistic partners would die without the mutualism; e.g. lichens) or facultative (i.e. the mutualism is “optional”, e.g. N-fixation symbiosis) www.notesolution.com - Other, less important, species-species interactions include: commensalism (0/+ relationship, e.g. Australian clownfish living in sea anemones: clownfish get protection, but anemones get nothing out of it; some gut bacteria are also in this category), amensalism (0/- relationship; e.g. gull excrement poisoning plants on rocky cliffs – gulls do not “care”), and neutralism (0/0 interaction – very rare in ecology) - The forces of competition and predation, and to a lesser extent mutualism (and others - see above), have continued to produce larger and larger biodiversity on Earth, interrupted only briefly by the mass extinctions of the past; today, more species are alive on the planet than ever before: most estimates place the number of species between 10 to 100 million, with only some 2.1 million identified with Latin names so far (in particular invertebrates, bacteria, and fungi are believed to have very many as yet undiscovered species) - The “megadiversity” areas are in the tropical rainforests: ~50% of all species live in the Amazon rainforest alone (in turn, these are mostly insects) - The natural rate of species extinction has been estimated to be 2 to 3 species per year; presently, species go extinct at at least 100 times the natural background level (Harvard entomologist E.O. Wilson estimates we might me losing as many as 20,000 species a year, again mostly insects) - Recent dramatic examples of human-caused species extinction include the passenger pigeon (last animal died in captivity in 1914; once the world’s most abundant bird with a population of 3 to 5 x 109) and the Labrador duck - Canada has ~138,000 species, 556 of which are officially considered at risk (e.g. marbled murrelet, Peary caribou, Vancouver Island marmot) www.notesolution.com - In the US, more than 80 million dollars are spent per year on the protection of just 10 (mostly cute and fuzzy) animal species (e.g. grizzly bear, Florida panther, manatee, bald eagle; less than 5 million dollars a year are spent on invertebrates and plants) - Walt Disney has done more harm to biology, esp. the proper evaluation of biodiversity issues, than almost any other public figure! - Major causes of species extinction (in order of importance) are: habitat loss (e.g. deforestation), exploitation (e.g. hunting), and introduction of exotic species (e.g. zebra mussels in the Great Lakes, Kudzu vine, Nile perch/cichlids in African rift lakes, marsupial displacement by introduced mammals in Australia), not global warming!! - Captive breeding programs have been implemented for many species that are considered to be on the brink of extinction (again, mostly for “charismatic” species), with some success stories (e.g. the California condor, the North American bird with the largest wingspan, was brought back from a near-extinction population of only 26 birds through zoo-based breeding efforts; offspring from these efforts have recently been successfully released into the wild) - Any such efforts are complicated by the very small genetic subsample in a small remaining population; this small genomic starting capital is afflicted by the expression of recessive traits at much higher frequencies than would occur in a large, randomly breeding population; this problem is referred to as inbreeding depression (human example: hemophilia, and similar recessive diseases, are overexpressed in the royal families of Europe, because of centuries of socially imposed inbreeding) - The concept of a species is pivotal to any biodiversity discussion and to conservation issues, but it is not always as easily defined as one might think (e.g. red wolf: recent www.notesolution.com mitochondrial DNA analyses show that the red wolf, formerly believed to be a distinct species threatened with extinction, is really a hybrid between the gray wolf and wild coyotes; moreover, red wolves will breed with gray wolves and coyotes under the right circumstances, i.e. even the more classical biological species concept breaks down in this case; likewise, a definition problem arises with strictly asexually reproducing “species”, such as bacteria; this is even trickier with viruses!) - Most biodiversity issues are as much ethical issues as they are biological ones! www.notesolution.comLECTURE 2324: - Unlike competition or predation, mutualism is a species-species interaction where both species benefit from the interaction - Important examples include: squids and Vibrio bacteria (bacteria are attracted to live inside a specialized light organ of the squids, protecting the bacteria from predation, and giving the squid the ability to change colour on account of the bacterias ability to produce bioluminescence); N-fixation symbioses; mycorrhizae (the close physical association between fungi and the roots of plants; the fungal partner enhances the nutrient acquisition capacity of the plant, esp. for phosphorus and nitrogen, while the plant supplies the fungus with carbohydrates; 80% of higher plant species are mycorrhizal, not just trees), lichens (composite organisms consisting of a fungus, known as the mycobiont, and an alga or cyanobacterium, known as the phycobiont; the mycobiont is very efficient at obtaining nutrient ions from the environment, while the phycobiont supplies photosynthate; lichens are critical components of primary succession, where they aid in the weathering of rocks and the production of soil), or intestinal bacteria (e.g. bacteria in the guts of termites enable termites to digest lignin from woody substrate; humans also have numerous symbiotic gut bacteria that aid in the digestion process; all these bacteria get shelter and nutrients from the host in return) - Mutualisms can also be non-symbiotic (such as between hummingbirds and the flowers they feast on), and may be either obligatory (i.e. the mutualistic partners would die without the mutualism; e.g. lichens) or facultative (i.e. the mutualism is optional, e.g. N-fixation symbiosis) www.notesolution.com
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