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The 130 ft French maxi-trimaran Banque Populaire V is 7 days into an attempt at the Jules Verne Trophy, the crewed RTW record, now 48 days. Lecture 37 - Ecology - Chapter 46 Some basic concepts in chapter 45 apply to the next few lectures, so please read it. How organisms interact with each other and the environment • Based on the molecular biology, cell biology, physiology, and behavior of animals. • Includes emergent properties that cannot be understood by a reductionist understanding of the biology of individual species: – “The whole is greater than the sum of its parts”. • Since we do not even fully understand the mechanisms underlying the biology of individual organisms, ecological processes are almost always studied in the absence of mechanistic understanding Niche Niche: – The entire range of biotic and abiotic interactions of members of one species with all others in its usual habitat, as well as with the abiotic features that facilitate the existence of a species in that usual habitat. – Sum total of all activities and relationships which individuals of a species engage in as they secure and use the resources required to survive and reproduce. Fundamental niche: – Widest range of abiotic and biotic situations a species could occupy Realized niche: – The niche a species actually occupies, given constraints of competition with other species Community • All the species that live together in a habitat • The habitat shapes a community’s structure – Climate and topography – Available foods and resources – Adaptations of species in the community – Interactions between species in the community – Arrival and disappearance of species – Physical disturbances 1 Interactions Between Species • Neutrality – Most common type of interaction • Competition – Interspecies competition is harmful to both species • Symbiosis – Commensalism • Helps one species and has no effect on the other – Mutualism • Helps both species – Parasitism • Harms one species for benefit of the other • Predation Competition • Most interactions between members of the same species are competitive. • Closely related species are clearly more likely to compete with each other than distant or unrelated species. • The Principle of Competitive Exclusion: – If two species occupy exactly the same niche, one of them will become extinct in areas occupied by both – Therefore, if 2 similar species seem to coexist in the same niche, they must actually have somewhat different requirements • E.g.: eating different size seeds, selecting flowers of different shape or color • Harms one species for benefit of the other Competition between 2 species of Paramecia that occupy identical niches Partitioning Resources Paramecium caudatum • If two species appear to share the same niche, and neither drives out the other, they are somehow dividing the resources so that, in actuality, they have different realized niches. White Black • Black and white rhinoceros Paramecium aurelia – Inhabit same area -- African savannah and appear very similar – Mouths differ • White rhinoceros has wide, flat mouth, eats grasses • Black rhinoceros has narrower mouth with extended upper lip, browses on branches & herbs Their names have nothing to do with their color! Both are grey. 2 Plants partitioning prairie soil with roots of different lengths Partitioning Niches (continued) • Insects – Several species may live off a single plant species, especially when the insect has overcome chemical defenses of a plant – One insect species may eat leaves; another seeds; a third, flowers: partitioning resources For the local toxic milkweed plants, butterflies (B) lay their eggs on the leaves which their caterpillars eat, while bugs (F) lay their eggs on the flowers and their larvae eat the developing seeds. Demonstrating Interspecies Competition: Exclusion Experiments • Two closely related species in the same habitat • Fence plots, excluding one species or the other • Observe alterations in Bristly foxtail Indian mallow Smartweed • Symbiosis: – Living together for at least some part of the life cycle, typically two quite different kinds of organism • Commensalism • Mutualism • Parasitism – plant growth – effects on numbers of remaining species • Conclusion: – greatest competition is between closely related species 3 Commensalism • Interaction between species that helps one of the species, and neither harms nor helps the other • Examples – Birds roosting in trees – Orchids growing on trees – Most of our gut bacteria? Mutualism • Both species benefit – Species very different from each other – Plant/animal interactions are common • May be obligatory – Yucca plants and yucca moth (right) • Each yucca species has its own moth species – Mycorrhizal fungi and plants • Orchids require these fungi to grow – Termites and protozoa in gut • Allow termites to eat wood – Ants nest in plants • Protection from herbivores • Some are more flexible – Honeybees • Gather nectar from many species • Efficiency of pollination also varies – Several species of insects may pollinate a species of flower Extreme mutualisms • Lichens are combinations of fungi with either a photosynthetic bacterium (cyanobacterium) or an alga (usually a green alga) • Most corals have obligate symbiotic photosynthetic bacteria living with them. Thats why most corals (except the deep sea variety), are in shallow water and colorful. “Bleaching” of corals is loss of their colorful photosynthetic partner and death. • Once again, mitochondria (all eukaryotes) and chloroplasts (in plants) result from endosymbiotic bacteria. Parasitism • Parasites drain nutrients from their hosts and live on or in their bodies. • Almost ubiquitous feature of animal life • Parasites on animals include – Viruses, Bacteria, Protists, Fungi – Invertebrates: – Nematodes, Platyhelminths, Insects – Vertebrates: – cuckoos, cowbirds Adult roundworms in pig intestine • Parasites on plants include other plants – Mistletoe • There are very few parasitic Archaebacteria or Archaea, and only parasitic on other Archaea 4 Parasitoids Predation and Population Cycles • Unlike parasites, parasitoids do kill their hosts, eventually • Most typically: insects, e.g. many wasps, some flies – Lay eggs on host, which is usually another insect • Larvae feed on host • Major method of biocontrol of insects, especially for Lepidoptera Parasitoid pupae emergent from a caterpillar host • Predators: • In single predator/prey – feed on other living organisms interactions – free-living - do not take up – Oscillations between residence on their prey population densities – Prey populations rise – Predator populations follow – Prey populations crash – Predator populations follow • Example: – Canadian lynx and snowshoe hare Ichneumon wasp Canadian Lynx and Snowshoe Hare • Note on graph: – cyclic oscillations – lynx are scarcer than hares • Krebs studied populations for ten years • Fencing plots delayed cyclic declines but didn’t eliminate them • More complex three-level model yields better fit – Aerial predators, plant abundance also involved Coevolution between Predators and Prey • Close interaction between 2 species may exert selection pressure on each, leading to alterations in both and an arms race – As snail shells thickened, claws of snail-eating crabs became more massive – Cheetah and its antelope prey are both extraordinarily swift runners – Plants produce toxic substances, insects detoxify them and sometimes not only live off the toxic species, but use the plant toxin as a defense for themselves. Canadian lynx (dashed line) Snowshoe hares (solid line) 5 Predator-Prey Adaptations • Toxic defense systems and aposematic coloration – Species that feed on toxic plants and sequester the toxin are often brightly colored. – Color warns predator not to attack • Cryptic coloration – Camouflage – Also used by predators • Monarch butterfly – Toxic defense systems • Mimicry – Harmless species mimics color pattern of toxic or dangerous species Yellowjacket Beetle Syrphid fly Community Stability Community • All the species that live together in a habitat • The habitat shapes a community s structure – Climate and topography – Available foods and resources – Adaptations of species in the community – Interactions between species in the community – Arrival and disappearance of species – Physical disturbances Non-stinging wasp • Eastern US communities include – Forests • Climax forests may be stable for centuries – Savannahs • Mix of grasses and sparse trees • Quasi-stable in the presence of periodic fires • Trees dominate if fires are suppressed – Prairies • Highly diverse • Very stable before Europeans came • Require fires to remain tree-free • Even stable communities may oscillate between species • In general, diversity increases community stability 6 Successional Cycles Secondary succession from corn field 20 years • Disturbed communities change over time • Primary succession occurs when plants first move into entirely new habitats – New volcanic islands, e.g. ferns first • Secondary succession occurs after a volcanic explosion or a fire – Mount St Helens in 1980 – Yellowstone fires in mid-1990s • Fireweed, grasses are first • Seeds of some conifers germinate only after a fire Destabilizing communities • Even climax communities can be destabilized by – Loss of crucial species Wolves and beavers in Yellowstone – Exotic species • Australia – Rabbits, cane toads • Hawaii – Pigs, goats, wasps • US – Kudzu in the south – Dutch elm disease – Zebra mussels – Other human intervention • Plowing the prairie • Draining wetlands Island Biogeography • The number of species likely to be found in a given area depends on – Size of the area • The number of species increases with the size of the area • Or: Area is directly proportional to species number – Distance from sources of species • The farther the distance from the colonizing source, the fewer species are found on the island • Or: Distance is inversely proportional to the number of species • Theory developed for true islands • Also holds for conceptual islands – Wilderness parks in a farmed area – Natural areas in disturbed setting • Prairie remnants in Illinois 7