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Section One Introduction
1.2 Ecological Methods
1.3 Spatial Scale
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1.2 Ecological methods
• Example: Study of Locust Outbreaks
– What causes outbreaks of locusts, which destroys crops and other vegetation?
– Development of study plan.
– Interaction web (Figure 1.8)
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NATURAL ENEMIESBacterial parasites Bird
predatorInsect parasites
COMPETITORS
Vertebrate herbivores
Other insects
PHYSICAL ENVIRONMENT
Physical extremes,such as temperature and moisture.
Host plant quality
Host plant quantity
FOOD AVAILABILITY
Fig.1.8 interaction web of the factors that could influence locust population size.
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Interaction web
• Natural enemies – Birds or other
vertebrates
– Insect parasites
– Bacterial parasites
• Competitors– Other insects
– Larger vertebrate grazers
• Host Plants
– Host plant quality
– Host plant quantity
• Physical factors
– Temperature
– Rainfall
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Where to begin
• Observations and Interpretations (Figure 1.9a, Figure 1.9b and Figure 1.9c).
Locu
sts
num
bers
per
m
% predation % predation % predation
(a) (b)(c)
Fig. 1.9 How locust numbers might be correlated with predation.
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Observations and Interpretations
• Statistical tests to determine significance of relationships.
• Causation vs. correlation.
• Experimentation – Predator study
• Hypothesis: Increased predators will decrease locust population.
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Experimentation
• Two study groups
– Treatment Group: Locusts with predators removed
– Control Group: Locusts with nothing done – predators present.
• Measurements
• Replications (Figure 1.10)
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Mean values
Predators removed
Predators still present
Locu
sts
num
bers
per
m 2
Fig. 1.10 a predator removal experiment
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Experimentation
• Statistical Tests
– ANOVA and t-tests.
– Means and Standard error
• Types of Experimentation
– Laboratory
– Field
– Natural
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Laboratory Experiments
• Most exact regulation of abiotic and biotic factors.
• Vary only the factor of interest.
• Disadvantage: Oversimplification of the biotic community.
• Best uses: Physiological responses of individuals.
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Field Experiments
• Conducted outdoors.
• Manipulation of abiotic or biotic factors (eg. Elimination of a competitor).
• Disadvantage: Methods of exclusion are unlikely to be generated by nature.
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Natural Experiments
• Uses natural perturbations to disrupt biotic community.
• Used to follow the trajectory of the perturbation over time.
• Results can be extrapolated to other communities.
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Experimental Problems
• Logistic problems lead to low replication
• Which leads to a Type I error; declaring that a hypothesis is false when in fact it is true. ( 否定 null 假說，但事實上是「 null 假說是成立的」 )
• Low replications lead to greater standard error (SE) values.
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two types of error in measurement
• type I error—the conclusion that there is an effect when in fact there is none, ( 否定 null 假說，但事實是「假說是成立的」 )
• type II error—when an impact exists but is not detected. ( 接受 null 假說，但事實是「假說是錯誤的」 )
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two types of error
• 自然現象的研究，盡量的下降 type I error 。– 盡量避免否定 null 假說。– 如此可以避免研究方向的錯誤。
• 然而，對於自然資源 ( 災害 ) 的研究，則需要選擇下降 type 2 error
– 譬如：漁業資源的耗減
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declining fish stocks
• Current management focuses on reducing type I errors because maximizing fish catch is of primary economic importance (Paully et al., 1998; Williams, 1998).
• However, scientific advice should be explicit about type II errors also, because the environmental consequences from type II errors are much more serious and take longer to recover from.
• Type I errors usually result in only short-term economic costs.
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Experimental Problems
• Difficulty in combining studies with differences in statistical power.
• Meta-analysis – a technique for combining studies.
– Meta-analysis weights different studies primarily on the basis of their sample size.
– Starts by estimating the size of the effect of a treatment from every experiment and then pooling all the effects together to get one overall effect size, usually called d.
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Mathematical Models
• Experiments may not be possible.
• Give valuable signposts on how natural systems might work.
• Indicate need for further data
• Indicate need for further observations.
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1.3 Spatial scale• A space occupied by an individual (behavio
r ecology)
• A local patch occupied by many individuals (a population)
• A large enough space to comprise multiple populations (a community)
• A biogeographic scale large enough to encompass a community, and its nutrients and energy cycles (an ecosystem).
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• Fig. 1.12 Determining the correct spatial scale
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Temporal Scale
• Proper choice of scale, depends on phenomenon and species studied.
• Short time scale studies for behavioral responses.
• Longer time scales studies for population dynamics and ecosystem processes.
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Discussion Question
• In a local park, forest, or even in your backyard think about five ecological questions you could ask and the information you would need to answer them.
• Do your questions relate to behavioral, population, community, or ecosystems ecology or do they cross categories?
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網路資源• http://www.prenhall.com/stiling
• The tools that you'll find on our site include:
• CHAPTER OUTLINES: help summarize all of the key information in the chapter.
• CHAPTER QUIZZES: self-grading quizzes for each chapter to help you reinforce your understanding
• CASE STUDIES: concise reviews and analysis of important ecological research
• DESTINATIONS: accurate, dependable Web sites
