6. Ecosystems tend to grow more diverse, complex and biodiverse over time, slowing and refining the passage of energy and nutrients through the system. Give some examples from a particular ecosystem of how this is or is not occurring.
Comment: Areas of the Amazon rainforest have as many as 200 tree species per acre, while the Siberian taiga averages one tree species per acre. The numerous tree species in the rainforest would each have unique insect and other species associated with them. Such high levels of diversity seem to be the result of ecosystem stability (constantly warm and wet) and interspecies competition—individual species become experts in a particular niche.
7. What is the relative net primary productivity (amount of biomass) of this ecosystem? Is it highly productive, moderately productive, or is primary production relatively low?
Comment: One way to measure net primary productivity is in calories of energy captured per square meter per year. Wetlands and rain forests are the most productive at about 9000 calories captured and stored per square meter. Temperate forests capture about 6000 calories, temperate grasslands 3000 calories, and deserts 500 calories.
8. What are factors limiting primary (i.e. photosynthetic) production?
Comment: Sunlight, water availability, temperature, nutrient availability, carbon dioxide level in the atmosphere, latitude, aspect, ecosystem disturbance and stability over time.
9. What are some factors limiting the overall carrying capacity of the ecosystem, and factors limiting the carrying capacity of a specific species?
Comment: Factors controlling overall carrying capacity are similar to factors limiting primary production (see above). Individual species are limited by food supply (including seasonal bottlenecks, like winter at high latitudes), water availability, predators, reproductive success, and intra-species competition.
10. How stable or unstable is the ecosystem? Is it at an early, mid- or late-seral stage? What are some of the factors controlling disturbance and succession?
Comment: This can be complicated…..while old trees may indicate a relatively stable ecosystem, old bitterbrush in our shrub-steppe suggests that humans have suppressed fire in the area and that the system is shifting from a grass dominated landscape to a shrubland. The scale is relative; some tropical ecosystems may change little for many thousands of years, whereas there was a mile of ice covering the Methow just 15,000 years ago. Our ecosystems can be rapidly set back to an early seral stage by fire and ice, water, insects and humans.
11. What are the assembly rules for the community? Who depends upon whom? Who arrived first? What is the likely succession scenario?
Comment: Colonizing plant species of bare land typically are annuals with limited needs for ecosystem relationships and services. They may, for example, be wind-pollinated, thus escaping the need for animal pollinators. Some weedy plant species reproduce asexually or self pollinate, obviating the need for a mate. Plants capable of fixing nitrogen (such as members of the pea family) are likely early seral species. Some plants need bare soil and bright sunlight to germinate and grow; other species are adapted to grow in humus and minimal sunlight.
12. What are some of the factors controlling disturbance and succession? Is the system subject to alteration by fire, water, storms, insects, grazing/browsing? How would potential early and late-succession plants disperse to the site?
Comment: Fire is obviously related to climate; the fire return rate for the Methow Valley’s shrub-steppe and ponderosa pine is about every 10 years (although frequent fires mean they will burn cool). That rate increases as you go up in altitude (because precipitation increases) or westward (ditto). The Pearrygin Creek blowout last year (2011) showed the power of alluvial fans; debris descended 2000’ down the mountain and sent water-borne debris onto the dry shrub-steppe at bottom of the hills.
13. Where does the garbage and waste in the ecosystem go?
Comment: There is no garbage and no waste in nature.
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