Ecology Exam 4 Answer Key (34 Questions)

EXAM 4: 1. Define ecological succession. Process of non-seasonal, directional change in an ecosystem whereby previous seral stages are replaced by subsequent seral stages until a mature climax community is established 2. What is a climax? Self-perpetuating, stable ecological community that is the endpoint of ecological succession; stable until disturbance. 3. Define disturbance. Event that removes biomass and opens up space and resources in an ecosystem. 4. What are 3 different ways that succession can start? They are all generally an event that removes existing biomass. Volcanic eruptions, change in river course produces sand/gravel bar, coastline sand dune formation 5. Define primary succession and give two examples. Succession that occurs in an area that never had soil or following a disturbance that removed the soil.  Occurs in an area that does not have soil  Volcanic eruption, glacial retreat 6. Define secondary succession and give one example. Succession that occurs in an area where the soil remains intact; fire. 7. Explain secondary succession in an old-field in Georgia. Explain the mechanism behind the changing in dominant species as time progresses. Why do shade-tolerant trees dominate after many years (>100)? Annual plants  perennial herbs  shrubs  light-demanding trees (pines)  shadetolerant trees (hickories, beech) Trees are the climax community. 8. (Primary/secondary) succession typically takes longer to reach the climax community. Why? Since there is no soil, it must be built and colonization must happen from outside species. 9. Explain primary succession on a glacial moraine. Lichens, mosses, herbs  alder  sitka spruce  hemlock  sphagnum bogs on poorly drained sites (only on wetter sites) 10. What typically has to happen first for succession to start in an area with primary succession? How do species colonize? First, there needs to be soil built. Then colonization from outside species. 11. Compare the two different approaches that ecologists use to study succession. Longitudinal approach:  Follow individual site from disturbance through climax community  Very long duration Static approach  Compare multiple sites at one point in time that differ in time since a disturbance  However, there may be differences in sites other than time (aspect, soil make-up) 12. List 6 characteristics of early successional species.  Many offspring  Small offspring  Rapid growth  Short lifespan  Small body size  Require abundant resources 13. List 6 characteristics of late successional species. o Few offspring o Large offspring o Slow growth o Long lifespan o Large body size o Tolerant of low resources 14. Are r-selective or k-selective species more likely to colonize early on? Which dominate later on? r-selective colonize early on, but K dominate later on. 15. Species diversity and richness (increase/decrease) as time goes on. 16. Evenness (increases/decreases) as time goes on. 17. Why are early successional communities generally species poor? There may be only a small pool of species that have the ability to disperse the disturbed site, and/or a newly disturbed site may also be a pretty harsh environment (sun, wind).  Dispersal ability  Harsh abiotic conditions 18. True/false. All plant species diversity peaks at intermediate successional stages. 19. Which plant species diversity species peak at intermediate successional stages and which peak in the climax community? Intermediate – tall shrubs and trees Climax – mosses and herbs 20. What is one reason that species diversity often peaks in mid-succession? Late succession species have not had time to colonize, but early successional species have not yet been competitively excluded 21. What are 2 reasons that species diversity peak in late succession? Complexity of habitat increases, creating more ecological niches, allowing partitioning of resources among more species. Great soil diversity, also tipped trees and pit. 22. Explain Hubbard Brook LTER. Bormann and Likens’ large-scale research into changes in ecosystem processes during succession. o Cut forest and suppressed growth with herbicides for 3 years to halt succession. o After herbicides were stopped, succession proceeded and nutrient losses decreased dramatically. o Showed that succession can reduce losses of plant nutrients caused by disturbance. 23. What is a weir? Sampling station for nutrient export in stream water. 24. What is a precipitation station? Measures nutrient input in precipitation. 25. What is the biomass accumulation model? Describe each stage. Four stages of forest succession characterized by different patterns in standing crop biomass and NPP. o Undisturbed ecosystem  disturbance  Aggradation  Transition phase  Steady state phase o Aggradation  Gross NPP far exceeds respiration  Photosynthesis at maximum rate  Greater amount of producers  Rapid increase in biomass and loss of nutrients o Transition – deaths of large trees? o Steady-state  Gross NPP and respiration converge  Constant biomass 26. As succession proceeds, nutrient cycling within the ecosystem becomes tighter.  Years with suppressed succession – high nutrient export o Reflects greater uptake of nutrients by plants when plants start to grow 27. What are the 3 hypotheses for the nature of interactions between early- and latesuccessional species? 1) Facilitation: early successional species change the ecosystem allowing later successional species to establish 2) Inhibition: early SS prevent establishment of late successional species, species replacement occurs when early SS die 3) Tolerance: late SS may experience competition from early SS, but they are able to establish and grow 28. Facilitation may be common in early stages of primary succession. 29. Facilitation may be important in secondary succession in harsh physical environments. 30. What are nurse plants? Give an example. Plant species that ameliorate harsh abiotic conditions allowing other plant species to establish (e.g. Palo verde as nurse plant for Saguaro seedlings) 31. What is the Monoclimax hypothesis? Clement’s hypothesis that for each climatic region there was a single climax species composition to which all successional sequences would converge. 32. What is the Polyclimax hypothesis? Tansley’s hypothesis that the climax community of a site was determined by topography and soil conditions in addition to regional climate – within a climatic region there could be multiple climax communities (e.g. Northern California – Pygmy, redwood) 33. What is ‘alternate stable states’? Give an example. For a single site there are multiple stable climax communities with the identity of the community that does establish determined by the nature of the initiating disturbance and chance colonization events. Deer initially suppress growth of trees which allows ferns to grow. 34. Is the theoretical climax community always achieved? Why or why not? No, because succession is continually being restarted by recurring disturbances – cyclic succession.