Biological Communities

1. Biological Communities • Community: all the organisms that live together in a specific place • ______________________ • _______________________ • _______________________ • ______________________ • Communities can be characterized either by their constituent species or by their properties • Species richness: the number of species present • Primary productivity: the amount of energy produced

2. Biological Communities • Two views of structure and functioning of communities • Individualistic concept: H.A. Gleason; a community is nothing more than an _____________________________that happen to occur together at one place • Holistic concept: F.E. Clements: a community is an integrated unit; _______________________________-more than the sum of its parts

3. Biological Communities Most ecologists today favor _______________________________ • In communities, species respond independently to changing environmental conditions • Community composition changes gradually across landscapes

4. Biological Communities • Abundance of tree species along a moisture gradient in the Santa Catalina Mountains of Southeastern Arizona • Each line represents the abundance of a different tree species • Community composition ________________________________________

5. Biological Communities • Sometimes the abundance of species in a community does change geographically in a synchronous pattern • ________________: places where the environment changes abruptly

6. Ecological Niche • Niche: the total of all the ways an organism uses the resources of its environment • _______________________________ • ______________________________________________________________________________________________ • Fundamental niche: the entire niche that a species is ____________________________________, based on physiological tolerance limits and resource needs • Realized niche:__________________set of environmental conditions, _____________________or _____________________of other species, in which the species can establish a stable population Billock

7. Ecological Niche • Interspecific competition: occurs ________________________________________________ and there is not enough resource to satisfy both

8. Billock Billock Ecological Niche • Other causes of niche restriction • ____________________absence or presence • Plant species • Absence of pollinators • Presence of herbivores

9. Ecological Niche Principle of competitive exclusion:___________________________________________________________________________________________________________________________________________ • G.F. Gause’s classic experiment on competitive exclusion using three Paramecium species shows this principle in action

11. Ecological Niche • Niche overlap and coexistence • Competitive exclusion redefined: no two species can occupy the same niche indefinitely _________________________ • Species may divide up the resources, this is called _____________________ • Gause found this occurring with two of his Paramecium species

12. Resource partitioning is often seen in __________________________________ that occupy the same geographic area • Thought to result from the process of __________________________________ Resource partitioning among sympatric lizard species

13. Ecological Niche • Character displacement: differences in morphology evident between sympatric species • May play a role in adaptive radiation

14. Ecological Niche • Detection of interspecific competition can be difficult • If resources not limited there may be no competition • Small versus large population size • May be environmental conditions that cause the decline of a species, not competition

15. Ecological Niche Detecting interspecific competition