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Approaches to Ecological Studies Outline • General Approach: Observation vs. Hypothesis Testing • Experimental Design and Statistical Analysis P.O. Ang, Jr. Biology Department The Chinese University of Hong Kong Ecological studies are ways to understand our mother nature ! STUDY NATURE, NOT BOOKS ! Louis Agassiz 1807-1873 STUDY NATURE, NOT BOOKS ! jus t STUDY NATURE, NOT Wikipedia ! jus t Field Observation STUDY NATURE through observation ! Hypothesis Generation UNDERSTANDING NATURE through hypothesis testing and experiments ! Field Validation Asking the Right Question Experimental Testing Field vs. Lab Works Field Observation Coral Reefs Ecology AFCD Photo Polyp and Skeletal Structure - Corallite - Septa - Coenosteum - Columella - Paliform lobe - Wall - Costae Veron 2000 Coral Growth Forms Massive / Submassive • Encrusting • Branching • Columnar • Tabular • Foliose • Laminar • Biology of Corals - Temperature: found in water mainly between 20o - - - to 35oC, optimal range is between 23o-25o C Light: corals need light because of the photosynthetic activities of associated zooxanthellae – limit the development of coral reefs in shallow water Salinity: corals are true marine organisms, grow best at 32 to 35 o/oo Sedimentation: corals are suspension feeders, have limited capability to clean sediments settle on them Exposure: corals cannot tolerate prolonged exposure to air Hong Kong Coral Community Dominant species ? Brain coral Dominant growth form ? Massive form Many fish ? No fish or very little if any Why ? How ? Tropical Coral Reef Field Observation Hypothesis to be tested Hypothesis Generation Field Validation Asking the Right Question Experimental Testing Field vs. Lab Works • Competition is the driving force behind dominance of certain species • Hierarchy of coral aggressiveness - Some corals are more aggressive than the others Field Observation Hypothesis Generation Field Validation Asking the Right Question Experimental Testing Field vs. Lab Works Strategies of Coral Competition Direct Competition: Use of Sweeper Tentacles Direct Competition: Use of Sweeper polyps Nematocysts (stinging cells) of Corals Direct Competition: Use of Mesenterial Filaments © Dickson Wong Indirect Competition: Over-Topping Direct Competition: Overgrowth © Dickson Wong Experimental Works on Coral Competition Vs. Veron 1986 Hypothesis to be tested • Competition is the driving force behind dominance of certain species • Hierarchy of coral aggressiveness - Some corals are more aggressive than the others Vs. Hierarchy of Coral Competition • Three types of competitive outcome: Winner, Loser or Stand-off • Ranking of coral abundance in nature vs. their aggressiveness Field Observation Hypothesis Generation Field Validation Asking the Right Question Experimental Testing Field vs. Lab Works Loser B A Winner © Connie Determine the Consequences of Competition: Winner, Loser or Stand-off Who is the Winner? A A B B © Connie Who is the Winner? Who is the winner? P.verweyi A.echinata P.acuta P.carnosus F.complanata F.pentagona A.digitifera P.ryukyuensis C P.decussata G.djiboutiensis A F.abdita F.rotumana C.serailia F.speciosa F.lizardensis F.flexuosa G.aspera L.undulatum L.purpurea Key: Standoff Direction of C.japonica M.peltiformis A.tumida Dominance B P.lutea T.peltata P.lobata © Connie P.aranetai Aggressive Ranking of Coral Species in Shallow Water Abundance of Coral Species vs. Aggressiveness Fig. (3) Relative Abundance of coral species in Shallow Water Region 25 20 Most aggressive species % 15 10 5 Platygyra acuta (brain coral) P. a P. cu ta ca rn os u P s L. . lu te pu a rpu F. re sp a ec P. iosa ar a ne G . tai a A . spe dig r a itif er P. P. lo a ry uk bata yu en F. s i s P. ab d i de t a cu C. s sat jap a on A ica F. .tu m pe id n ta a F. g on a fle F. x u os ro tu m a P. ana ve rw A eyi F. .glau liz ard ca en G . F. v s i s dji er bo o n u M tien i .p e si lti s fo r T. mis pe lta ta 0 Species Hong Kong Coral Community Field Observation Hypothesis Generation Field Validation Asking the Right Question Experimental Testing Field vs. Lab Works More Hypotheses to be generated and tested Use of Oxygen probe • Other biological forces, like predation, may be playing a critical role • Other physico-chemical factors may be important etc… Use of Pulse Modulated Fluorometer Simple Observations and Experiments in Different Field Environments Experimental Design vs. Statistical Analysis • Experiment – Mensurative (Observation) vs. Manipulative • Sampling - Replication vs. Control - Pseudoreplication • Differential tolerance to temperatures of fish, invertebrates: to test on survival, growth and dominance of different species • Clearing experiments to observe succession of species: Pioneer (rselected) species vs. K-selected species Finding Trends in Long Term Monitoring 45 @AFCD Ice Cover in Lakes Experimental Designs for Hypothesis Testing: Sampling Statistical Analysis: Mean values being compared Study on the effect of certain chemicals Y and Z on fish growth Study on the effect of certain chemicals Y and Z on fish growth Control (no chemical) Control (no chemical) Four fish per tank: replicates Four fish per tank: replicates Measure the change in length Y Z Treatments ic Cho ct s orre c f eo ode al m c i t tatis Measure the change in length Y Z Treatments an port m i ls t !!! Statistical Analysis Statistical Analysis - Common Statistical Models: - Parametric vs. Non-parametric Statistics - Common Parametric vs. Non Parametric Models - t test vs. Mann Whitney U Test for two sets of sample - Analysis of Variance (ANOVA) for > two sets of sample - One Way ANOVA vs. Kruskal-Wallis One Way ANOVA - Parametric statistics: Testing difference between mean values - Assumptions of Parametric Statistics: - Randomness and Independence - Normal Distribution - Equality of Variance - Non-parametric statistics: testing difference between rank orders or median - Parametric tests more powerful Sampling Sampling Replication vs. Pseudoreplication (Independent vs. not independent) Replication vs. Pseudoreplication Control Control Mean value Y Y Z Mean value Z Mean value Sampling Replication vs. Pseudoreplication Sampling Sampling error involving puedoreplication committed when using parametric statistics like t test or ANOVA for evaluation I I II II III III Summary - Careful field observation important in ecological studies - Better understanding of nature processes can be gained by experimental testing of hypotheses - Important to have proper experimental design and use of statistics to evaluate results of experiment - More questions raised after experiments - This is how we understand nature TO STUDY NATURE IS BOTH FUN AND CHALLENGING ! Thank you…!
