Welcome to BIOL 207 – General Ecology Fall 2010/2011

1. Welcome to BIOL 207 – General EcologyFall 2010/2011 1

2. www.greenresistance.wordpress.com Know that site. 3

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5. Extra Credit 8 5

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7. Index cards for chapter 1? Remember: we’re using a new book this semester 2

8. Chapter 1: Introduction 10

9. ? “Where we humans fit in a less than perfect world is a judgment each of you must make, guided by your own sense of values and moral beliefs. Regardless of your own stand, it will be more useful to you and to human kind in general if your judgment is informed by a scientific understanding of how natural systems work and the ways in which humans are a part of the natural world.” 12 9

10. other important questions • what is ecology • what do ecologists do • what are ecologists interested in • where did ecology emerge from in the first place • ... what is its relationship to my life? 10

11. What is Ecology? …. Oikos = home “By ecology, we mean the body of knowledge concerning the economy of nature -- the investigation of the total relations of the animal both to its organic and to its inorganic environment; including above all, its friendly and inimical relation with those animals and plants with which it comes directly or indirectly into contact -- in a word, ecology is the study of all the complex interrelationships referred to by Darwin as the conditions of the struggle for existence.” Ernst Haeckel, 1870. 13 11

12. So, what is ecology? • Ecology is the science by which we study how organisms (animals, plants, and microbes) interactin and with the natural world. • in that case - ecology is the oldest science! • early ecologists were applied ecologists. how so? • ecology is also a ‘pure’ science - understanding for the sake of understanding • ecologists strive to develop an understanding of very basic and apparent problems in a way that recognizes the uniqueness and complexity of all aspects of nature but seeks patterns and predictions within the complexity 14 12

13. Ecology - A Science for Today • We have a great need for ecological understanding: • what are the best policies for managing our environmental support systems -- our watersheds, agricultural lands, wetlands? • we must apply ecological principles to: • solve or prevent environmental problems • inform our economic, political, and social thought and practice Example? 15 13

14. So what do ecologists do? • They try to explain and understand • Two different classes of explanation in biology: proximate and ultimate • Proximate explanation: what is going on ‘here and now’ • The present distribution and abundance of a particular species of bird may be ‘explained’ in terms of the physical environment that the bird tolerates, the food it eats, and the parasites and predators that attack it • Ultimate explanation: answer in evolutionary terms • How did this bird come to have these properties that now govern its life… • Ecologists must describe before they explain… • Ecologists also try to predict what will happen to x under y

15. Scales, diversity, and rigor • Ecological phenomena occur at a variety of scales • Ecological evidence comes in a variety of different sources • Ecology relies on truly scientific evidence and application of statistics

16. Questions of Scale: Ecological Systems Large and Small • Individual Organism(“No smaller unit in biology ... has a separate life in the environment...”) • Population (many organisms of the same species living together) • Guild (a group of populations that utilizes resources in essentially the same way) • Community (many populations of different kinds living in the same place) • Ecosystem (assemblages of organisms together with their physical environment; community + physical environment) • Biosphere (the global ecosystem, all organisms and environments on earth) 17 16

17. ecological systems 17

18. Ecological systems… human view 19 18

19. Perspectives of Ecologists: Organism Approach • How do form, physiology, and behavior lead to survival? • Focus is on adaptations, modifications of structure and function, that suit the organism for life in its environment: • adaptations result from evolutionary change by natural selection, a natural link to population approach… ? - Why are trees the dominant plants in warm, moist environments – and shrubs the dominant plants in regions with cool, wet winters and hot, dry summers? 21 19

20. Perspectives of Ecologists: Population Approach • What determines the numbers of individuals and their variations in time and space? • Focus is on processes of birth and death, immigration and emigration, influenced by: • the physical environment • evolutionary processes • interactions with other populations, a natural link to community approach… ? – Why have mosquitoes increased in number and in extent? 22 20

21. Perspectives of Ecologists: Community Approach • How are communities structured from their component populations? • Focus is on the diversity and relative abundance of different kinds of organisms living together, affected by: • population interactions, promoting and limiting coexistence • feeding relationships, responsible for fluxes of energy and materials, a natural link to ecosystem approach... ? – what is the relationship between birds, crops, and insects? 23 21

22. Perspectives of Ecologists: Ecosystem Approach • How can we account for the activities of populations in the common “currencies” of energy and materials? • Focus is on movements of energy and materials and influences of: • organisms large and small • climate and other physical factors, including those acting on a global scale, a natural link to biosphere approach... ? – movement of Nitrogen… ? 24 22

23. Perspectives of Ecologists: Biosphere Approach • How can we understand the global movements of air and water, and the energy and chemical elements they contain? • Focus is on the global circulation of matter and energy, affecting: • distributions of organisms • changes in populations • composition of communities • productivity of ecosystems ? – climate change ?! 25 23

24. Questions of scale: time scales • Ecologists also work on a variety of time scales • Ecological Succession – the successive and continuous colonization of a site by certain species populations, accompanied by the extinction of others • Can be studied from weeks (decomposition?) … to thousands of years (ice age to present) • Migration • Can be studied in butterflies (days…) or in forest trees (thousands of years … or decades)

25. Systems and Processes: Dimensions in Time and Space • Nothing in nature is static: anything we can measure (conditions, number of organisms) exhibits variation. • Variation has temporal and spatial components. • Variation in each measurement has a characteristic scale; for the same degree of change: • air temperature varies over hours • ocean temperature varies over weeks or months (weather vs climate?) 47 25

26. Temporal Variation • Consider two kinds of temporal variation: • predictable, cyclic variations (daily, seasonal) • unpredictable, irregular variations • A temporal “rule of thumb”: • the more extreme the condition, the less frequent (compare cold fronts and hurricanes) … but… • but frequency and severity are relative terms that depend on the organism! 48 26

27. Spatial Variation • Spatial variation occurs at very small (forest sunflecks) and very large (latitudinal variation in solar flux) scales. • Scale of variation importance is a function of the organism: • the two sides of a leaf are different to an aphid • a moose eats the whole leaf, aphid and all 49 27

28. Time and Space • A few generalizations: • moving organisms experience spatial variation as temporal variation • the faster an individual moves: • the smaller the scale of spatial variation • the more quickly it encounters new environments • the shorter the temporal scale of variation • spatial and temporal scales are correlated • frequency is inversely related to extent/severity 50 28

29. Diversity of ecological evidence • Observations and field experiments • Controlled Laboratory experiments • Simple laboratory systems • And mathematical models

30. Ecology Employs the Scientific Method induction observation hypothesis ormodel experiment prediction deduction 60 30

31. What is an hypothesis? An hypothesis is an idea about how the world works: • e.g., “Frogs sing on warm nights after periods of rain.” We often wish to understand two components of such a phenomenon: • how? (encompasses physiological processes) [how does a frog respond to temperature and rainfall?] • why? (encompasses costs and benefits of the behavior to the individual) (how to answer..) 61 31

32. Experiments test predictions. • Hypotheses generate predictions: • if observations confirm the prediction, the hypothesis is strengthened (not proven) • if observations fail to confirm the prediction, the hypothesis is weakened (or rejected) • Best tests of hypotheses are experiments: • independently manipulate one/few variables (or trick frogs into singing on a ‘wrong’ night) • establish appropriate controls 62 32

33. Some Potential Pitfalls • A correlation between variables does not establish causation. • Many hypotheses cannot be tested by experimental methods because: • the scale is too large: • patterns may have evolved over long periods • the spatial extent is too large for manipulation • causal factors cannot be independently tested 63 33

34. Some Approaches to Difficult Problems • Mathematical models are powerful tools: • researcher portrays system as set of equations • model is an hypothesis and yields predictions that can be tested; examples include: • models of disease spread • models of global carbon • Microcosms are sometimes useful: • microcosms replicate essential features of the system in a laboratory or field setting 64 34

35. Microcosms…communities of freshwater invertebrates 35

36. Hypothesis: bird predation on insect herbivores reduces the amount of leaf area consumed. Field Study: construct bird-proof cages to allow insects freedom of movement. 36

37. Yes: insects increased 70% -> leaf area % lost increased 22% to 35% • So? • Leads to important question: Will the decreases in bird populations caused by fragmentation of forests in the eastern US and elsewhere result in increased insect damage to forests? Other questions? 67 37

38. Statistics and scientific rigor • True of false: you can prove anything with statistics • You cannot prove anything with statistics • Statistical analysis attaches a level of confidence to conclusions that can be drawn • In ecology –as in all sciences – we search for confident conclusions, not provable truths

39. Rigorous (accurate, exhaustive) Science • Based on conclusions that are the results of investigations carried out with the express purpose of deriving those conclusions • Based on conclusions to which a level of confidence can be attached, measured on an agreed scale • -- note Boxes 1.2 and 1.3 and 1.4

40. Ecology in practice • Let’s examine some more real research programs • 3 main points • Ecological phenomena occur at a variety of scales • Ecological evidence comes from a variety of different sources • Ecology relies on truly scientific evidence and the application of statistics

41. Brown trout in NZ Much can be learned by comparing ecology of streams containing trout with those occupied by non-migratory native fish in the genus Galaxias Question: is the native Galaxias (on the right) hiding from the introduced predator? • Effects on individuals, populations, communities and ecosystems • Understanding enhanced (naturally) when links between all these levels are made clear(er) • Brown trout (Salmo trutta) – introduced to NZ in 1967 from Europe

42. Brown Trout: examining the individual level What are the consequences for invertebrate feeding behavior? Mayfly nymphs of various species: are there differences in their activity rhythms depending on whether they are in Galaxias or trout steams? In a Galaxias stream: active both day and night In a trout stream: daytime activity most reduced

43. Brown Trout: examining the individual level Conclusions derived from both readily controlled conditions of a lab experiment and from the more realistic and more variable circumstances of a field experiment • Trout rely primarily on vision to capture prey • Galaxias rely on mechanical cues • Thus: invertebrates in a trout stream more at risk of predation during daylight hours

44. Brown trout: population level How does brown trout impact the distribution of native fish? At each site, a variety of physical variables were measured Using statistics,  ?: which physical variables (if any) distinguished one type of site from another ? A: Galaxias restricted to sites upstream of waterfalls [cannot be climbed by trout]. Why? Direct predation by trout on native fish below waterfall • 198 sites selected. • Streams of similar dimensions chosen at random in each of 3 tributaries from each of 8 subcatchments of the river • Sites: (1) no fish; (2) Galaxias only; (3) trout only; (4) both Galaxias and trout

45. Brown trout: community level ? Do these changes have community consequences that impact other species ? Trout -> lower invertebrates -> higher algae • Do trout affect the stream food web differently from the displaced Galaxias? • 3 treatments established (no fish; Galaxias; trout) at naturally occurring densities in several randomized blocks in a stretch of stream. Algae and invertebrates – and then fish introduced and then algae and invertebrates sampled

46. Brown trout: ecosystem and energy flow • ? Will the rate at which radiation energy is captured through photosynthesis by the algae be greater in the trout stream? • Annual net primary production (rate of production of plant – i.e. algal – biomass) six times greater in the trout stream than in the Galaxias stream • ? In the trout stream, will the higher primary production be associated with a faster rate of uptake by algae of plant nutrients (nitrate, ammonium, phosphate) from the flowing stream water? • Also yes. • Conclusion: a trophic cascade is responsible for the patterns observed at the ecosystem level

47. Succession… • Ecological succession – what is it? • Excellent place to study: old agricultural fields in the eastern US, abandoned by farmers • What have the studies at Cedar Creek illustrated? • What is the natural successional sequence of plants? • From this understanding: an artificial manipulation can be planned; historical records can be examined

48. 22 fields at different stages in an old-field succession (abandoned between 1927 and 1982) were surveyed in 1983; 22 ‘snapshots’ • Correlations! • ?: are the correlations in (a) – (d) the result of an effect of field age – or is the causal agent nitrogen with which age is correlated?

49. Artificial experiments: search for causation • 6 replications. Two fields (one abandoned for 46 yrs; one for 14 yrs); nitrogen manipulations • Questions: • (1) do patches receiving different supply rates of nitrogen become less similar in species composition over time? • Yes. But 10 years later, plots receiving different amounts of N had diverged in species composition. The greater the difference in N input, the greater the divergence • (2) do patches receiving similar supply rates of nitrogen become more similar in species composition over time? • At the start, different. After 10 years, plots within the two fields subjected to similar rates of N had become remarkably similar

50. Artificial experiments: search for causation • Time itself is not the only cause of successional changes in species composition • Differences in available nitrogen cause successions to diverge; similarities cause them to converge much more quickly than they would otherwise do • Time (= opportunity to colonize) and nitrogen are clearly intimately intertwined. More unanswered ecological questions. • Know the Hubbard Brook study