BirdnestS22.pptx

Nest predation: Developing a question and purpose:

Example of a scientific question: Does nest height matter for influencing nest predation?

Remember developing a question(hypothesis) for scientific research must meet the following requirements:

Testable

Repeatable

Measurable; through statistical analysis

Should be influenced by the scientific literature

Should have a reason for testing; i.e., Why do we care, or why is it important to society, the environment, the public, etc.

Tentative Location: (M,W, F classes)

Flat Rock State Natural Area

2381 Factory Road,

Murfreesboro, TN 37130

860 17’ 43”W, 350 51’ 30”N

Analyzing Ecology:

Independent variables: factors that are presumed to cause other variables to change.

Dependent variables: factors that are being changed.

Example:

We hypothesize that variation in the nest condition has led to different predation rates.

Independent variable = Nest condition

Dependent variable = Predation

* Experimental unit = nest

5.5ft

Use transects and marking them

Map it or sketch it

Assign treatment/control conditions along transects

Random table generator or random # table

Pattern

Random

Combination

Layout experiment

Brown Egg Nest

Speckled Egg Nest

POSITIVE SIGNS OF PREDATION

For this class we focus on Chi Squared Statistical Method:

“Goodness of Fit” Test

2X2 Contingency Table analysis

It is intended to test how likely it is that an observed distribution is due to chance. It is also called a "goodness of fit" statistic, because it measures how well the observed distribution of data fits with the distribution that is expected if the variables are independent.

Data	High Nest	Low nest	Total
Predation	5	6	11
No Predation	11	10	21
Total	16	16	32

Data Collection:

Dependent Variable 

Independent Variable 

Pred/No	Trt.	Obs.	Calc.	Calc.	Expected
Pred	high	5	Col1 x row1/Total	(16 x 11)/32	5.5
Pred	low	6	Col2 x row1/total	(16 x 11)/32	5.5
No Pred	high	11	Col1 x row2/total	(16 x 21)/32	10.5
No Pred	low	10	Col2 x row2/total	(16 x 21)/32	10.5

How to calculate expected frequencies:

Data	High Nest	Low nest	Total
Predation	5	6	11
No Predation	11	10	21
Total	16	16	32

Pred/No	Trt.	Obs.	Exp.	(Obs – Exp)2 /Exp
Pred	High	5	5.5	(5 – 5.5)2/ 5.5	0.045
Pred	Low	6	5.5	(6 – 5.5)2/5.5	0.045
No Pred	High	11	10.5	(11 – 10.5)2/10.5	0.024
No Pred	Low	10	10.5	(10 – 10.5)2/10.5	0.024
				Sum of Chi-square	0.139

Calculating Chi-square:

From the observed and expected frequencies

x2 = Σ(observed – expected)2

expected

x2 = (5-5.5) 2+ (11-10.5) 2+ (6-5.5) 2+ (10-10.5) 2

5.5 10.5 5.5 10.5

x2 = 0.139

Hypothesis – Additional info and X2(Chi square):

H0: The height of the nest has no effect on predation of eggs

HA: The height of the nest does have an effect on predation of eggs

Each group will have a X2(chi square critical value of 3.841), so if the calculated test statistic is…..

≥ critical value means that it supports the hypothesis of a difference (reject Ho)

≤ critical value means that it does NOT support the hypothesis of a difference (accept Ho))

Interpretation

Because our x2 is less than the critical value for p = 0.05, we fail to reject the null hypothesis

There is no significant difference in the predation of nests placed high versus nests that low

X2 = 0.139

critical value (from table, p = 0.05) = 3.84

0.139 < 3.84

Your Project:

Model birds find at Flat Rock

Lists on D2L

Control & treatment

Manipulate Nest or egg

Shape, size, color, materials, or decoy

BirdnestS22.pptx

BirdnestS22.pptx

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