Most animals insects too composed of 23 water by

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most animals (insects too) composed of 2/3 water by weight – they all need to maintain whatever ratio they require to survive - mammals – can withstand 10% loss -15-20 % often fatal - some frogs can lose as much as 40% of their body water - loss of water can be via evaporation form skin - problem for animals with permeable skin eg worms and amphibians
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- lost via respiration, excrement, other secretions Environmental Gradients and Species’ Niches (organism/environment interactions Geographic range (of a species) – the entire area where a species can be found – regardless of whether it is common or rare - differences in abundance of species within its range is referred to as its density - Measure of population abundance per unit of area - # of individuals /m^2 or ha, # individuals /m^3 aquatic systems Which species is more vulnerable - Sometimes there is overlap, and sometimes not – this can be a force for evolutionary change or some other change (eg. Move to a new location) Competition - “is a mutually detrimental interaction between individuals” - Reduced growth, survival and reproduction - Interspecific competition: individuals of two or more species - Intraspecific competition: individuals of the same species - The general forms of competition - Stenophagy clearly limits distribution of the predator to where the prey exists – despite the capability of the predator to tolerate a wider range of environmental conditions than the prey - It seems like a poor strategy - LOOK FOR ADVANTAGES Prey range – limited by predator distribution - Much harder to document cases - What about the affect a euryphagus predator might have on restricting the geographic distribution of prey species - Many of the best examples are associate with freshwater fish populations - Native fish not adapted to large generalist predators –evolved in isolated lakes, streams, springs for 1000’s of years - We expect stenophagous predator populations and their prey species to undergo periodic fluctuations in population size – Lotka-Volterra model - But recent experiments show hare populations fluctuate when predators are excluded – food supply variation results in periodic cycles – echoing the hare-plant cycle Symbiosis: Mutualism, Commensalism and Mimicry Symbiosis- close association between two species that generally develops through co evolution - Often the association is necessary for survival of one or both species - Obligatory nature of relationship means there is biological control on geographic distribution of one or both species - Different types of symbiosis Mutualism – close interaction of different species benefits both species Commensalism – benefits one species and has no impact on the other
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Concepts to explain - Some different types of interspecific interactions that may control population distributions and geographic range - Why might an animal evolve stenophagous behaviour - Explain the competitive exclusion principle in the context of competition between and within species - The Lotka-volterra model and some of its limitations -
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