Focus on the Biota: Metabolism, Ecosystems and Biodiversity

Transcription

1 Chapter 9 Major environmental issues associated with Global Change on short-time scales Focus on the Biota: Metabolism, Ecosystems and Biodiversity Global Warming Stratospheric Ozone Depletion Deforestation and Loss of Biodiversity Components of the Earth system through which elements (such as C) recycle. The biosphere plays an important role in many interactions and in the recycling of elements. Fundamental characteristics of life that allow it to interact with the physical processes that occur on the planet in such a way that Earth is a habitable planet. 1. Life spreads exponentially 2. Life needs energy 3. Life pollutes 4. Life is versatile 2 ways for classifying life: 1. in a systems-way according to processes, related to the use of energy and other interactions with the ecosystem 2. Taxonomy, with regards to the physiological and evolutionary relationships between organisms 1

2 Recall that CO 2 and CH 4 are greenhouse gases - methanogenous are important as either (a) autotrophic or (b) heterotrophic (a) CO 2 + 4H 2 CH 4 + 2H 2 O (b) CO 3 COOH CH 4 +CO 2 The net result of the activity of methanogenous and oxygenic photosynthesizers is to release O 2 and CH 4 to the atmosphere: Oxygenic photosynthesis: 2CO H 2 O CH 2 O + 2O 2 Fermentation: 2 CH 2 O CH 3 COOH Heterotrophic methanogenesis: CH 3 COOH CH 4 + CO 2 NET: CO H 2 O CH 4 + O 2 SIGNATURE OF LIFE Lovelock points out that our atmosphere is far from chemical equilibrium, but obviously dynamically stable. Chemical Equilibrium: All reactions have an equilibrium constant associated with them, which indicates the ratio of products to reactants (depending on temperature and other conditions). For example: H 2 CO 3 H+ + HCO 3 - carbonic acid bicarbonate K=4.4E-7 atm mixed layer (CO 2 ) g THE INORGANIC CARBON CYCLE: interaction with the biological pump (CO 2 ) aq H 2 CO 3 HCO 3 - CO 3 2- SIGNATURE OF LIFE Lovelock points out that our atmosphere is far from chemical equilibrium, but obviously dynamically stable. Without biological processes (i.e. life), the atmosphere would be in chemical equilibrium (such as exists on other planets). The fact that the atmosphere of our planet is in a state of chemical disequilibrium is a signature of life! In fact, one way to try to identify the presence of life on other planets is to see if the atmospheric constituents are in equilibrium or not. Yet, the chemical composition of the atmosphere has been very, p p y stable over long periods of time because of the systems dynamics, which includes the biogeochemical cycles in which life plays an important role. 2

3 Structure of the Biosphere species all closely related organisms that can potentially interbreed. Possible feedbacks between the boreal forest and climate - from experiments conducted with a General Circulation Model change all forest north of 45N to bare ground and compare to actual forest equivalent to moving forest line south population all the members of a single species that live in a region community 2 or more groups of interacting species biome region with a characteristic plant community (desert, boreal forest) ecosystem communities with the physical environment that supports them negative coupling Implied by Model Results positive coupling Model Results positive feedback 1. increase in wintertime albedo trees prevent snow from covering homogeneously the area less trees more snow on bare ground - albedo increased 2. decrease in Tair in April about 12 deg C drop in T 3. colder T in winter leads to increase in sea-ice cover which in turn leads to higher albedo of the area 4. this further higher albedo leads to a decreased Tair 5. Implied by this results: more sea-ice keeps SSTs lower decreasing the ocean s thermal content which keeps high-latitude Tair unusually low and so the forest is prevented from re-growing We might say that the forest keeps the climate that it needs to grow healthily: it prevents winter T from being dangerously low for its own survival! The figure presents a systems diagram of the feedbacks involving boreal forest cover, albedo, temperatures, sea ice, and the oceans. The diagram helps us see that it is possible for the northern boreal forest to have a significant impact on the larger-scale climate. Now use information you have about the possible impacts of anthropogenically induced greenhouse climate change and this diagram to discuss the implications in terms of climate and forest cover (Critical-Thinking Problem 1). What do you already know? That anthropogenically induced greenhouse change is a warming trend in the earth s climate, and in particular that this means increased winter temperatures. So the question can be re-stated now: according to the system diagram of this figure, what are the implications of increased winter temperatures for the climate and forest of high latitudes? Warmer winter temperatures would lead to a decrease in sea ice, which would lead to a decrease in albedo and an increase in sea-surface temperatures (SSTs). The increased SSTs lead to increased highlatitude summer temperatures, which would lead to increased boreal forest cover. The increase in boreal forest cover would lead to a decrease in albedo. The decrease in albedo resulting from both increased boreal forest cover and decreased sea ice would lead to higher winter temperatures. In sum: this would be a positive feedback cycle that would accentuate the climatic changes caused by global warming. 3

4 Ecosystems overlap, gradually merge, transitional boundaries: ecotones Decomposers Feed on dead d organic matter from all levels who-eats-whom diagram food chains are interconnected as food webs Trophic levels series of feeding levels The amount of biomass decreases by 1-2 orders of magnitude (90-99%) at every level. Why? Interactions between species can be cooperative, mutually supportive bees and trees: one gets food the other reproduces. An extreme form of this support is symbiosis coral and plantlike dinoflagellates. Another extreme is complete competitive i coexistence, but less often than one might think. Disruptions of ecosystems dynamics is generally followed by a predictable pattern of rebuilding succession. Unpredictability (Stochastic Processes) in these patterns leads to diversity. Biodiversity Measures of Biodiversity Diversity of Interactions Diversity = Stability? 4

5 homogeneous Measures of Biodiversity Simpson s diversity index measures the likehood (probability) that two individuals chosen at random from the same community will be of different species : S d = Simpson s diversity = 1 - [(P A ) 2 + (P B ) 2 + (P C ) ] heterogeneous where P A is the proportion of species A (B, C, etc.) in the community = probability that an individual chosen randomly will be of species A (B, C, etc.). In this example: S d = 1 - (0.99) 2 + (0.01) 2 = 0.02 Community I S d = 1 - (0.5) 2 + (0.5) 2 = 0.50 Community II Assignment 1-To discuss next class Take A Closer Look at Physiology vs Ecological Optimal Growth Box, page 178 Read it once to understand the basic concepts. Then 1. Explain the graphs of figure Describe briefly, but clearly, the two paradoxes referred to in the text of the box 5