1 An overview on ecosystems: 2 Ecosystems: units with boundaries that can be isolated for study [as any system] 3 Ecosystems

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1 1 An overview on ecosystems: n What are they? n What are their important characteristics? n How are they organized? 2 Ecosystems: units with boundaries that can be isolated for study [as any system] 1. Hierarchical: complex, adaptive, emergent Fig. 3-4 (D&R) or Fig. 3.9 (KR8B) 3 Ecosystems 4 Terrestrial vs aquatic ecosystems n The predominant biomass in forests is in trees (the bottom of the food web) n Yet the predominant biomass in aquatic systems is in fish/mammals (oceans) at the top of the food chain n Something significantly different is going on in these different systems! n Furthermore, in between these two extremes are grassland/savannah systems where the predominant constituent of biomass are the herbivores (grazers like buffalo, antelope, etc.), the middle of the foodweb n How do we understand these differences? In spite of boundaries... and differences n All ecosystems remain interconnected and interdependent Terrestrial biomes are connected by rivers Sediments/nutrients from land wash into aquatic ecosystems All share a common hydrologic cycle and a common atmosphere n All species on Earth (along with their environments) could be considered one vast ecosystem (landscape): the biosphere n But inherently impractical as a unit of study 8 If everything is connected to everything else,... n How many ecosystems can be degraded or destroyed before we see effects on the entire biosphere? n To what extent can basic global elements be altered (e.g. the atmosphere and its temperature, the ocean and its chemical composition) before all ecosystems are affected? n What are the implications for the long-term persistence of humans? 9 The characteristic structure of ecosystems I 1.The environment (abiotic factors) Tolerance range of an individual Tolerance ranges of the population - niche Adaptation of populations/acclimation of individuals Natural Disturbance Unpredictable (earthquake, volcano, tsunami, human activity) Somewhat predictable (fire, flood, changes in vegetative cover, soil chemistry) Anthropogenic Disturbance 10 The characteristic structure of ecosystems II Abiotic Factors n The degree to which abiotic factors are present or absent/high or low affects the ability of

2 organisms to survive. n Since each individual in a population/species may have a slightly different (genetically determined) response to a particular factor, populations will differ in their responses to the abiotic environment, reflecting the sum of individual variation n The nature of a particular ecosystem will be a result of this underlying variation in both abiotic factors and populations responses 12 For every environmental factor and every population If we drew a graph for every variable (abiotic or biotic) affecting a species, we would have a picture of a species niche 14 n For any particular population, numbers (or density) will be highest where all relevant environmental conditions are optimal. n Some organisms have generally wide ranges of tolerance (generalists). Other have narrower ranges (specialists). n Those with wide tolerance ranges (generalists who have broad niches) can live in a variety of habitats. Those with narrower ranges (specialists with narrow niches) have more restricted distributions. 15 Fundamental vs. realized niches n However just having a wide tolerance range (a wide fundamental niche) does not guarantee a species will occupy the whole of the niche 16 Liebig s law of the minimum n Restricting any one of the many different environmental factors that influence an organism will limit the population n e.g. plants need water, light, nutrients and proper temperatures for growth n Even if water, nutrients and light are optimum, the plants cannot survive and prosper if temperatures are above or below their limit of tolerance n Ecologists expend considerable effort trying to quantify species niches and the population s most likely limiting factor(s) 17 Draper or Draper/Reed Designating large areas as biomes is somewhat of an oversimplification given the 3 dimensional structure of landscapes 21 Space and time! 22 In aquatic systems, moisture is irrelevant but temperature, light, nutrients and a variety of biological interactions remain important variables regulating species 23 distributions 24 Microclimates

3 n Even with latitudinal/altitudinal considerations, there will be small spaces or patches in an environment that have temperature, moisture, light, nutrient or other conditions significantly different from the overall regime (e.g. a south-facing slope or sheltered ravine, proximity to a creek, the shade of a rock or tree) n Similarly, a given aquatic site may have temperature, light or nutrient conditions that are significantly different than the open water (e.g. upwellings or coral reefs in the ocean, streamside vegetation in a river, sunken logs in a lake) n Specific conditions found in a localized area (patch) are referred to as its microclimate 25 Microclimates II 26 For animals, patchiness is also relative to the organism s size and speed: Grain 27 biotic as well as abiotic factors structure ecosystems 1.Trophic relationships: predator/prey or foodwebs (producers, consumers, decomposers) 2.Non-feeding relationships (competition, symbiosis) 28 The nature of relationships n Don t worry about the names of the interactions just yet! n Just note there are 3 possible outcomes n Both species benefit; only 1 species benefits but the other is unharmed; one benefits, the other is harmed 29 Feeding relationships: food webs 30 In spite of the variety and apparent complexity of foodwebs, they all have the same underlying trophic pattern Secondary (2 o ) consumers or carnivores (also heterotrophs) Primary (1 o ) consumers, grazers or herbivores (heterotrophs) Producers, usually plants or autotrophs 31 The relationship between producers and consumers is one we have seen before as the carbon cycle n Autotrophs (self-feeders) feed themselves through photosynthesis (the process of turning inorganic carbon into organic carbon and capturing energy) CO 2 + H 2 O <=> C 6 H 12 O 6 + O 2 n Heterotrophs (other feeding) feed themselves by consuming organic carbon already fixed by autotrophs and extracting its energy via respiration that energy is then available for growth reproduction, etc. (though they have to get rid of the CO 2 ) C 6 H 12 O 6 + O 2 <=> CO 2 + H 2 O 32 A heterotrophic web we often ignore is that of the detritivores Energy also helps us understand the limits of food webs n The 2 nd law of thermodynamics tells us that there will be an inevitable loss of useful energy (or an increase in entropy) with the progressive movement to higher and higher

4 trophic levels. n Eventually there will not be sufficient energy to support an additional trophic level. n Most ecosystems are characterized by 3 (terrestrial) or 4 (aquatic) trophic levels. 35 Thermodynamics also helps us understand the ecological consequences of ever increasing meat consumption by humans 36 Non-feeding relationships Symbiosis Mutualism Commensalism Parasitism (are these just teeny-tiny carnivores?) 37 non-feeding interactions: symbiosis (mutualism) 38 Mutualisms 39 Speaking of mutualisms! 40 non-feeding interactions: symbiosis (commensalism) 41 Cool but complicated commensals 42 non-feeding interactions: symbiosis (parasitism) 43 Some parasites have little contact with their hosts 44 Symbioses within symbioses Competition: Recall the wood warblers and the difference between their fundamental and realized niches 47 Why does it matter whether species compete for the same resource? 48 There appears to be an advantage to co-existing or avoiding competition: optimizing allocation of energy n If an organism can avoid spending time competing with other organisms, it can spend more time (and devote more energy) to finding a mate, reproducing and caring for young (increasing the chances that its genes will persist into the next generation in the form of more offspring) n Perhaps at the expense of the organisms who spend more of their time competing 49 Similarly to Fig 3-11 (D&R): Rather than competing, these 5 species of warblers avoid competition by partitioning their habitat or by co-existing (over long evolutionary time, each has developed a unique approach to feeding) The species of organisms we see coexisting today may be the result of competitive interactions that took place thousands or millions of years ago (the ghost of competition past)

5 50 Plants also exhibit strategies to avoid competition over nutrients, water, light or pollinators (i.e. co-exist) 51 Species of wood warblers or planaria or plants represent examples of avoidance of interspecific competition. However organisms might also compete with other members of their own species (intraspecific competition) with similarly negative results Differentiation between larvae and adult, e.g. larval caterpillars and adult moths or butterflies, is assumed to be a mechanism to avoid intraspecific competition 52 Territoriality is another mechanism for avoiding intraspecific competition 53 n Over time (and assuming a reasonably stable environment), random genetic changes (mutations) could confer on some individuals an increased ability to better exploit a narrower segment of the resource gradient. n These individuals thus avoid niche overlap and potential competition (whether intra or inter). n IF this proves successful (i.e. the individuals with this characteristic leave more offspring than individuals without the characteristic), then over time more and more individuals of that species will come to possess the characteristic over time n The result is that the population will be ever more finely tuned to its environment! 54