7   

Scientific Research Paper

You will write a lab report using the scientific format of introduction, methods, results, and discussion to report the findings of this lab. You need to search the literature on edge effects for your introduction and to support or to compare with your conclusions for the discussion section of your paper (citing your literature as shown in the format given to you previously).

Things to think about in your paper:

Why are the potential factors causing differences in species richness and/or abundance between edge and interior habitats? What are some of the things that explain this difference from the literature?

Why was canopy cover presumed to have an effect on the species richness and abundance of arthropods in the forest? What other data that you collected might be useful in analyzing the arthropod species distributions? How would you analyze them?

If you had null results (no significant difference between habitats and/or no strong correlations) for your experiment, what are the potential reasons?

What are the differences, if any, in the types of species and their population sizes that occur in the two different habitats? How would you analyze this? Suggest some possible statistical analyses in the discussion section.

Potential literature sources:

Murcia, C. 1995. Edge effect in fragmented forests: implications for conservation. Trends in Ecology and Evolution 10:58-62.

Hernández-Santin, C., M. Cuautle, M.N. Barranco-león, J. García-Guzmán, E.L. Badano, F. Luna-Castellanos. 2019. Eucalyptus edge effect on Quercus-herbivore interactions in a Neotropical temperate forest. Neotropical Entomology. https://doi.org/10.1007/s13744-019-00694-5

8   

Research Paper in Ecology

Forest edge effect on species richness and abundance of arthropods at BOLOS

Scoring Rubric

Introduction (20 pts)

 Is the topic clearly and concisely introduced?  Is there a sufficient literary review of the topic of edge effect?  Does the information forecast the remainder of the paper?

Methods and Results (25 pts)

 Methods are logically organized with adequate description of materials and methods used to gather data.

 Results contain tables and/or graphs used to depict species numbers in different habitats.  Results contain the use of statistical methods to illustrate whether there is significant difference in

arthropod distribution between forest interior and edge habitats.  Linear regression equation is computed and used to draw best fit line between the plots.

Discussion and Conclusions (35 pts)

 Primary literary sources (peer reviewed) are used to support or refute the edge effect on arthropod community patterns.

 Discusses the impact of related research on the concept of edge effect.  Summarizes the evidence with respect to thesis statement (that arthropod species richness and

abundance are or are not affected by edge effect).

Grammar and Mechanics (10 pts)

 Grammatical errors or spelling does not detract from the paper. Literature Cited (10 pts)

 Literature is listed alphabetically and in the format required.  At least 5 sources cited and listed from this section are primary literary sources

1

Lab 10 Forest Edge Effect (Data Analysis) Objectives:

 To compare arthropod species richness and abundance between forest edge and interior habitats at BOLOS.

 To fit simple linear regression model on arthropod species richness and canopy cover.

 To fit simple linear regression model on arthropod abundance and canopy cover.  To plot the data of arthropod species richness against canopy cover.  To plot the data of arthropod abundance against canopy cover.

Background Information

To compare the abundance and species richness (α diversity) of arthropods between forest edge and interior habitats, we will use analysis of variance (ANOVA). Although fairly robust, this method makes some assumptions about the data, so we need to test those assumptions about our data first.

1. What are some of the assumptions of ANOVA and how can they be tested?

To examine the relationship between the species richness of arthropods and some environmental characters (e.g., canopy cover %), we will use simple linear regression. This statistical method analyzes the statistical relationship between two quantitative variables (predictor and response) with hypothesized causality between them (Fig. 10.1).

2

A simple linear regression model represents the relationship between the mean (expected value) of the response and the predictor by the function

μy = a + bx,

where x is the predictor, y is the response, and a is the intercept. Notice that y does not always equal to a + bx. Rather, the observations have variations around the regression line and their mean (μy) is given by the function.

A linear regression model makes a few assumptions:

1. The mean of responses (μy) at each predictor value (xi) is described by a linear function of xi.

2. The errors of responses are independent. 3. The errors of responses at each predictor value are normally distributed. 4. The errors of responses at different predictor value have equal variances

(σ2).

Sometimes the linear regression relationship between the predictor and response entails transformation of both variables. A common transformation is the log10 transformation, which gives the data points a better fit to the linear regression model.

We will model the abundance of arthropods by the canopy cover percentage using simple linear regression in R. You will then plot the two variables and draw the least squares linear regression line.

2. What is α (alpha) diversity?

3. Which variable is the predictor? Which variable is the response?

Fig. 10.1. Liner regression between predictor (x) and response (y). https://cdn-images-1.medium.com/max/1600/1*LEmBCYAttxS6uI6rEyPLMQ.png

3

Activity

Work in groups, download the OneDrive spreadsheet as an Excel file. Next, import the data into R, using RStudio. Be sure to select the correct sheet from your Excel file, and give it a concise name that’s easy to type with no spaces (e.g., yourDF). You can view your data frame by clicking on it in the RStudio Environment.

We first need to create two new variables in our data frame, the α (alpha) diversity and total abundance for each cover board (row). Use this line of code to create a column named “Alpha”:

yourDF$Alpha <- rowSums(yourDF[,c(9:21)]>0)

Use this line of code to create a column named “Abundance”:

yourDF$Abundance <- rowSums(yourDF[,c(9:21)])

Now let’s test for the normality and homogeneity of our data. We will first test normality using Q-Q plots. We will do this for both alpha diversity,

qqnorm(yourDF$Alpha) qqline(yourDF$Alpha)

and abundance.

qqnorm(yourDF$Abundance) qqline(yourDF$Abundance)

Normally distributed data plots should look something like Fig. 10.2. Any major deviations from the line suggest non-normality.

We will then test the homogeneity of the variances our data using the Bartlett Test.

bartlett.test(Abundance~Habitat, data = yourDF)

The hypotheses tested by the Bartlett test are:

H0: σ12 = σ22 = … = σk2 Ha: σi2 ≠ σj2 for at least one pair (i,j).

H0 is rejected if p < 0.05. Fig. 10.2. Q-Q plot of normally distributed data.

4

To perform ANOVA, use the R function aov().

yourmodel1 <- aov(Alpha ~ Habitat, data = yourDF)

summary(yourmodel1)

yourmodel2 <- aov(Abundance ~ Habitat, data = yourDF)

summary(yourmodel2)

4. What are the p-values for each model?

5. Is the null hypothesis rejected for each metric (alpha diversity and abundance)? Why or why not?

Next, we will perform the linear regressions of alpha diversity and abundance based on canopy cover. However, it turns out that R does not like the “%” character in the title of the “Canopy_cover_%” column of the data frame, so let us fix that first. We will do so by making a new column in our data frame with a simplified title “Canopy” and copy the values from the original column. Use this line of code:

yourDF$Canopy <- yourDF$`Canopy_cover_%`

To construct simple linear regression model on the predictor and response variables, use the lm() function. First, construct the model for alpha diversity:

canopyreg1 <- lm(Alpha~Canopy, data = yourDF)

Then show results of the regression using the summary() function.

summary(canopyreg1)

5

6. What are the p-values for the intercept and the predictor (canopy)? Is this model a good fit for the data? Why or why not?

7. What is the linear function of this simple linear regression model?

Now plot the transformed variables and draw a regression line through the data points. Use the following codes:

attach(yourDF)

plot(Canopy, Alpha, xlab = “Canopy cover %”, ylab = “no. of species”)

abline(lm(Alpha~Canopy), col = “red”) #drawing regression line

Save a copy of your plot. Does the regression line look like a good fit?

Repeat the linear model construction and graph plotting for arthropod abundance against canopy cover. Copy the R codes that you used below:

6

References

Engineering Statistics Handbook. Bartlett’s Test. https://www.itl.nist.gov/div898/handbook/eda/section3/eda357.htm

Pardoe, I. 2018. STAT 501 Online course material website. The Pennsylvania State University. https://newonlinecourses.science.psu.edu/stat501/

Quick-R. Assessing Classical Test Assumptions. https://www.statmethods.net/stats/anovaAssumptions.html

Sokal, R. R. and F. J. Rohlf. 1995. Biometry: the principles and practice of statistics in biological research. W. H. Freeman and Company, New York, NY. 887 p.

See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/49757343

Edge Effects in Fragmented Forests: Implications for Conservation

Article  in  Trends in Ecology & Evolution · February 1995

DOI: 10.1016/S0169-5347(00)88977-6 · Source: PubMed

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ECOLOGY, BEHAVIOR AND BIONOMICS

Eucalyptus Edge Effect on Quercus-Herbivore Interactions in a Neotropical Temperate Forest

C HERNÁNDEZ-SANTIN1, M CUAUTLE1 , M DE LAS N BARRANCO-LEÓN2, J GARCÍA-GUZMÁN1, El BADANO2, F LUNA-CASTELLANOS1

1Depto de Ciencias Químico Biológicas, Univ de las Américas Puebla, Cholula, Puebla, Mexico 2División de Ciencias Ambientales, Instituto Potosino de Investigación Científica y Tecnológica, San Luis Potosí, Mexico

AbstractKeywords

Quercus , herbivory, edge effect, Lepidoptera caterpillars

Correspondence M Cuautle, Depto de Ciencias Químico Biológicas, Univ de las Américas Puebla, Cholula, Puebla, Mexico; [email protected] hotmail.com

Edited by Martin F Pareja – UNICAMP

Received 18 June 2018 and accepted 26 April 2019

* Sociedade Entomológica do Brasil 2019

Fragmentation leads to the formation of edges between habitats, which in turn changes biotic and abiotic factors that might influence herbivory or plant-herbivory interactions. The aims of this study were to describe the herbivory community associated with oak (Quercus) and to determine the effects of proximity to a Eucalyptus edge and season on insect herbivory. We selected three forest sites that were subsequently divided into three quadrants located at different distances from the Eucalyptus edge: edge (0 m), intermediate (30 m), and oak forest interior (60 m). We randomly selected 10 oak trees per quadrant and conducted monthly surveys, during the dry and rainy season (from February to October 2010), where we quantified leaf area and the percentage of herbivory. These were analyzed using linear mixed models, with distance and season as fixed factors and individual and site as random factors. The primary oak herbivores were Lepidoptera caterpillars. We found that herbivory increased away from the edge but just during the rainy season, although higher herbivory levels were found during the dry season. These results seem to be related to a specialist community of herbivorous associated to the Quercus. This study emphasizes the importance of considering border effect, especially within Natural Protected Areas to establish strategies to improve and maintain native oak forest and the biodiversity of its Lepidoptera herbivorous community.

Introduction

Landscape modification due to anthropogenic activities (e.g., land conversion to agricultural or livestock) has resulted in habitat fragmentation, one of the major threats for forest conservation (Buckley 2000, Franklin et al 2002). Fragmentation is defined as the disruption or breakdown of large vegetation patches into smaller ones resulting in a dis- continuity of resource distribution that affects species occu- pancy, reproduction, and/or survival (Franklin et al 2002). One of the important features of this phenomenon is an increase in edge length relative to the forest area, particular- ly in small habitat fragments (Laurance 1991, Laurance &

Yensen 1991, Murcia 1995, Laurance et al 2007, De Carvalho Guimarães et al 2014). Edges are defined as bound- aries between distinct patches types, so edge identification depends on how patches are defined (Ries et al 2004, Wirth et al 2008). Both physical (light, humidity, solar incidence; Buckley 2000, Murcia 1995, Williams-Linera et al 1998) and biotic conditions (e.g., plant-insect interactions, species and resource distribution) are strongly altered in forest edges relative to interior (Lidicker 1999, Bogaert et al 2001, López 2004, De Carvalho Guimarães et al 2014), and these changes are referred to as edge effects (Wirth et al 2008). The chang- es in the physical environment are followed by changes in forests structure and species composition and abundance

Neotrop Entomol https://doi.org/10.1007/s13744-019-00694-5

along the forest edges (Ries et al 2004, De Carvalho Guimarães et al 2014). Finally, changes in species composi- tion may result in modified species interactions (De Carvalho Guimarães et al 2014).

The ecological consequences of edge effects have been mostly studied in terms of effects on biodiversity and species abundance and distribution (Lidicker 1999, Bogaert et al 2001, López 2004, Medinaceli et al 2004, Connor 2006), whereas studies on edge effects on species interactions such as herbivory have received relatively less attention (but see, Baraza et al 2004, Bossart and Opuni-Frimpong 2009, Liang & Stehlik 2009, Rossetti et al 2014, De Carvalho Guimarães et al 2014). Herbivory, defined as the consumption of plant tissue by animals (Strauss & Zangerl 2002), is the most wide- spread plant-insect interaction and represents an important determinant of vegetation structure (Medinaceli et al 2004). There are two types of herbivory: external herbivory occurs when herbivores feed on leaves, flowers, and seeds, whereas internal herbivory takes place under the plant’s surface and is caused mainly by insects that cause galls or mines (Strauss & Zangerl 2002). A meta-analysis (31 studies) of the effects of fragmentation on herbivory, performed by De Carvalho Guimarães et al 2014, found a significant increase in insect richness (65%), insect abundance (14%), and plant herbivo- rous rates (74%) on edges, compared with vegetation inte- riors. They also found that herbivorous rates were higher when herbivorous were chewers of the Orthoptera and Lepidoptera orders. AccordingtoDe CarvalhoGuimarães et al 2014, edges can be considered postdisturbance recovering sites, in which plant species number and/or densities incre- ment, representing extra resources for generalist herbivo- rous. This study is in accordance with the revision (55 studies) made by Wirth et al (2008), who found that 82% of the studies reported that edge promotes a positive effect on herbivorous response (abundance, species richness).

In the study area, the native vegetation is oaks forest and the main herbivores are Lepidoptera caterpillars. Oaks (Quercus spp.), from the Fagaceae family, are a group of trees and shrubs distributed throughout the Northern hemi- sphere including Europe, Asia, and North America (Vázquez et al 2004). In Mexico, oak-dominated forests cover 5.5% of the country’s land total surface and include 161 Oak species of which 109 are endemic (Arizaga et al 2009). Based on this, Mexico is considered a center of diversification of oaks in the American continent (Vázquez et al 2004). In the Neotropics, oaks are widely distributed, ranging from the north of the Mexican Transition Zone down to the south of the Colombian Andes, and it includes the greatest oak species diversity re- gion in the mountains of southern Mexico (Rodríguez-Correa et al 2015). The main insect herbivores on oak species belong to Lepidoptera and Hymenoptera which feed on leaf tissue during the larval stage (Summerville et al 2003), and Lepidoptera in particular represents a dominant group of

herbivores on oak by causing up to 88% of the external herbivory on these tree species (Hochwender et al 2003, Williams-Linera & Herrera 2003). Previous work with oak herbivory has found that it is influenced by abiotic factors such as light availability (Baraza et al 2004, Liang & Stehlik 2009), as well as biotic factors such as the age and size of the plant (Medinaceli et al 2004), plant tissue type (Baraza et al 2004), and tissue quality (Murakami et al 2005).

The state park “Flor del Bosque” is a Natural Protected Area (SEMARNAT-CONANP 2013–2018), located in Puebla (Mexico), which has an oak forest. However, in recent de- cades, increasing demand for firewood and clear cutting to establish Eucalyptus spp. plantations have resulted in dra- matic effects of fragmentation in the oak forests (Costes- Quijano et al 2006). The given condition in the study area is similar to other Natural Protected Areas that present some degree of the environmental deterioration caused by land use change, pollution, and habitat fragmentation (Cruz- Elizalde et al 2015, Ochoa-Ochoa et al 2009). Given the pres- ent condition of the study area, understanding Eucalyptus edge effects on species interactions occurring within oak for- est stands is of vital importance for conserving insect diver- sity and oak native populations. The questions addressed in this study included the following: (1) What are the primary external herbivores of the Quercus species in a neotropical temperate forest? (2) What is the Quercus-related effect of proximity to Eucalyptus edges on external herbivory? (3) Does external herbivory varies among seasons (dry and rainy)? We hypothesized that insect herbivory associated with Quercus would decrease away from Eucalyptus spp. edges. It is expected that external herbivory will be higher at the Eucalyptus spp. edge and will decrease gradually to- ward the forest interior. In the study zone, most of the but- terflies reproduce in the rainy season (Barranco-León et al 2016), so we expect higher herbivory in this season.

Materials and Methods

Study area

The Natural Protected Area “Flor del Bosque” is located in the state of Puebla, Mexico (between 19°00′00″ and 19°01′ 50″N, and 98°20′35″ and 98°20′53″W). The study area has sub-humid temperate weather with rains during the summer (June–September) while a markedly dry season occurs during the rest of the year (Cwb in Köeppen classification), an an- nual mean temperature of 18°C, and mean annual precipita- tion of 800 mm. Relative humidity ranges from 42 to 67% depending on levels of precipitation. The Natural Protected Area covers a total of 664 ha of which 255 ha (41%, of the total area of the protected area) is constituted by oak forest, 9.3 ha (1.5%) is covered Eucalyptus plantation, and the

Santin et al.

remaining 400 ha is covered mostly by pasture (Costes- Quijano et al 2006).

Oak forests include 10 oak species (Badano et al 2010). In general, forest patches found within the park are highly dis- turbed and trees tend to be small in stature and highly branched. The dense vegetation present in these areas gen- erates more humid conditions and lower light availability, and the dense forest cover prevents rainfall from reaching the ground directly (Barranco-León et al 2016).

Eucalyptus patches are represented by two species, Eucalyptus camaldulensis Dehnh and Eucalyptus globulus Labillardière, which were introduced more than 45 years ago. In contrast to oak forest patches, Eucalyptus stands allow much higher levels of rainfall to reach the soil (81%) and are characterized by greater light availability (Barranco- León et al 2016).

Herbivore community

The main external herbivores that were observed feeding on Quercus species were Lepidoptera. Internal herbivory was also observed, done by insects that cause galls or mines. In this study, we refer to just external herbivory caused by Lepidoptera. From September 2009 to October 2010, Lepidoptera caterpillars that were seen feeding on Quercus spp. were collected and taken to the laboratory for observa- tion until metamorphosis. In each case, the host tree species was recorded. Caterpillars were reared at the Entomology Laboratory of the Universidad de las Américas Puebla and maintained at room temperature (20°C) and 60% relative humidity. Within the rearing room, caterpillars were individ- ually placed inside a 2.5-L plastic container or a plastic bag. Old leaves fed to caterpillars were periodically replaced by new leaves. Date of pupation was recorded for each cater- pillar. When necessary, the containers were filled with a mix- ture of dry leaves and dirt for the caterpillars to dig in and pupate. After metamorphosis, adults were sacrificed for identification. All Lepidoptera were identified to the mini- mum taxonomic level possible using the proposed identifica- tion keys from Borror and White (1970), Borror et al (1992), Marshall (2006), Powell & Opler (2009), and mounted spec- imens were revised by Ph. D Hantke and determined to species. Oaks from which caterpillars were collected were identified whenever possible to species using the Rzedowski and de Rzedowski (2001) key for oaks.

Study design

Due to the fragmentation process that has occurred in the park, the oak forest patches are of different size and border Eucalyptus plantation or pastures. We selected three oak forest patches (i.e., hereafter “sites”) that were bordering a Eucalyptus plantation, to standardize for Quercus-Eucalyptus

border. In each site, we delimited three 20 × 20 m quadrants. The quadrants were established at the edge (0 m from the Eucalyptus stand), 30 m from the edge (intermediate zone), and 60 m from the edge (forest interior).

Within each quadrant, we randomly selected five trees each of Quercus castanea Née and Quercus obtusata Bonpland. These two oak species were chosen because they were abundant and/or its determination to species was pos- sible. Determination of Quercus spp. was just possible for the site two and three. The diamet