Lec2Part2EEMB2W08

Lec2Part2EEMB2W08 - Factors Limiting Distributions(Biotic...

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1 Factors Limiting Distributions (Biotic Interactions - Other Species ) The local distributions of many organisms are limited by the presence of other organisms (biotic interactions) (Competition, Predation, Parasites, Disease ) Competition: can occur between 2 or more organisms or species that exploit the same types of limited resources and live in the same geographical area Competition: (- , -) interaction - Intraspecific - competition within a species - Interspecific - competition between two different species Interference competition - Direct physical interaction over resources Exploitative competition - Indirect interaction over resources Species A Species B Resource Species A Species B Resource Factors Limiting Distributions (Competition) 1) When species A is absent, species B lives in a wider range of habitats (Competitive Release) 2) If competition is strong, the geographic ranges of the two competitors may not overlap but have sharp boundaries Natural patterns indicating competition: Joseph Connell (UCSB) - pioneer of experimental marine ecology, British coast (1961) - Intertidal zone - British coast (1961) Example: Factors Limiting Distributions (Competition) Balanus Chthamalus - Barnacles 1) Balanus (large) 2) Chthamalus “thamalus” (small) Intertidal zone: Barnacles species are found in discreet zones as adults (No overlap in distribution) - But larvae settle in all regions Balanus (Large) Chthamalus (Small) High tide level Mean tide level Settlers Adults Settlers Adults Rock Factors Limiting Distributions (Competition) Why is there zonation? What limits the distributions of Balanus and Chthamalus?
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2 Transplant experiment: - For both species, move Chthamalus low & Balanus high Factors Limiting Distributions (Competition) Upper limits set by desiccation: - Chthamulus can close tighter than Balanus Ch B Spring: marked out quadrats (.1m
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