Formicidae Biodiversity in Texas Vegetation

A COMPARISON OF FORMICIDAE BIODIVERSITY IN NATIVE AND NON-NATIVE VEGETATION IN SOUTH TEXAS

A study to determine how ant communities in non-native vegetation, specifically in Cenchrus ciliaris, differ from native vegetation in south Texas.

ABSTRACT

When non-native grasses become invasive, they can alter plant communities and can therefore, potentially affect arthropods due to their relationships with the vegetation they reside on. Cenchrus ciliaris is a non-native grass to the United States and is commonly known as buffel grass. Its drought resistance and quick propagation has made buffel grass invasive and has changed the ecosystems they now reside. Ants will be sampled from patches in native vegetation and buffel grass in San Ygnacio for 12 months. This study seeks to determine how ant communities in predominantly Cenchrus ciliaris, differs from relatively undisturbed native vegetation in south Texas. I pursue to compare ant richness between native vegetation and buffel grass as well as compare richness and abundance between native ant species and non-native ant species. I expect the results to demonstrate lower ant richness and abundance in the locations with buffel grass and higher abundance of invasive species in buffel grass.

Introduction

The introduction and spread of invasive plants is a cause of concern worldwide (Blossey 1999; Didham 2005). The ability of humans to travel between different countries around the world has facilitated the introduction of non-native plants to new locations. These new environments usually lack the natural predators and other natural biological control factors, thus causing these plants to become invasive. (Keane & Crawley 2002; Tallamy 2004). Invasive plants can also have characteristics that aid their establishment and survival. For example, some of these plants can have a higher tolerance to drought or can propagate more quickly. They can also create unfavorable conditions for native plants by altering soil litter and nutrients (Bakker & Wilson 2001). Therefore, invasive plants can often out-compete native plants, resulting in lower vegetation diversity and abundance (Pimentel 1999; Bakker & Wilson 2001). Many species of plants have been introduced into the United States, and although a relatively small percentage of these species negatively impact the ecosystems they invade, studies should be done on specific invasive plants to determine the negative impacts they may be causing to the environment.

Buffel Grass

Cenchrus ciliaris is a non-native grass to the United States and is commonly known as buffel grass. It is native to most of Africa, southern and southwestern Asia, and Italy, Sicily. Buffel grass was originally introduced to Texas (U.S.A.) and northern Mexico in the 1930s and 1940s to improve pasture in overgrazed habitats and to develop new rangelands (Cox et al. 1988). Its drought tolerance and high biomass productivity made it the most popular grass to use in these countries (Arriaga et al. 2004). Due to its commercial value and impact as a weed it is considered a contentious species. Although the agricultural benefit of buffel grass is controversial, buffel grasslands can be a threat to biodiversity because they are created by invading and removing native plants (Arriaga et al. 2004; Cox et al. 1988). The threat that buffel grass poses to the native vegetation and alteration of the ecosystem, can have an effect from birds to arthropods. Buffle grass appears to provide a less suitable habitat for breeding birds, especially bird species that forage on or near the ground (Bingham et al. 2006). While changes in plant litter can alter arthropod abundance (Wolkovich 2009).  Buffel grass is also associated with increased severity of fires by a buffel grass-initiated fire invasion feedback (Miller et.al 2010). Despite the serious environmental effects buffel grass may cause, there are no national strategies to manage it (Marshal et al. 2011).  Understanding the effects buffel grass has on biodiversity in south Texas can bring insights on whether there is a serious threat to other native vegetation and ecosystem functions.

Arthropods: Formicidae

Arthropods have many ecological roles within an ecosystem, functioning as prey resources for many taxa, as important predators, and as pollinators and seed dispersers (Isaacs et al. 2009). Recent studies document how plant invasions contribute to arthropod abundance (Wolkovich 2009). Changes in the vegetation cover can have an effect on arthropod diversity and are therefore used as indicators of negative effects on an environment. An important arthropod that is very diverse, does not fall into a single functional group, and can be classified as herbivores, predators, and detrivores, are ants (Triplehorn & Johnson 2005). Ants (order Hymenoptera, family Formicidae) are relatively well-studied and easy to identify to the species level (Wolkovich et al. 2009). Structure and composition of ant communities can reflect the nature of the environments in which they reside on. Ants are also commonly used as bio-indicators in studies for fire management, pesticide contamination, and habitat disturbance (Burbidge 1992).  Reduction in ant species abundance, diversity, and richness has been documented when alterations of ecosystems occur, for example, an increase of invasive plants (Burbidge 1992; Wolkovich et al. 2009). Therefore, this study will be measuring ant richness and abundance to determine how ant communities in non-native vegetation, specifically in Cenchrus ciliaris, differ from native vegetation in south, TX. This will further our understanding of the effects that buffel grass has on the ecosystem.

METHODS

Study Sites

Study plot areas were selected in San Ygnacio, TX. The study area was comprised of a mixture of grasses and shrubs. Native grasses included knotroot bristle grass (Setaria parviflora), Texas Grama (Bouteloua rigidiseta), Common Curly Mesquite (Hilaria belangeri) and tanglehead (Heteropogon contortus). Predominant native shrubs included honey mesquite (Prosopis glandulosa), guajillo (Acacia berlandieri), and blackbrush (Acacia rigidula). The non-native grass was predominantly buffel grass. The soil in the study site was mostly sandy and dry. The native areas where traps will be placed were selected based on the abundance of native vegetation and lack of buffel grass, while the areas for the non-native traps will be placed where buffel grass is the most predominant plant.

Sampling

It was determined that surveying arthropods was a more cost-effective and accurate design for assessment of biodiversity (Oliver & Beattie 1996) Direct sampling with pitfall traps seems to be the optimal collection method for surveying ants so it will be the method of collection that will be used in this study (Jaffe & Romero 1989). There will be six pitfall traps placed in predominantly native vegetation and six pitfall traps in areas that are predominantly invaded with buffel grass. The pitfall traps will contain either propylene glycol or alcohol glycol for trapping and conservation of the arthropods. These traps will be place at ground level and will each be labeled accordingly; N for native and B for buffel grass. Each of these traps will have their GPS coordinates and the nearest vegetation to the traps recorded. They will be left out for a week and they will be collected by hand for a year.

Ant Sorting and Identification

After the traps are collected ants will be sorted into separate vials labeled with their respective trap number and date. All the other arthropods collected in the traps will be sorted to order. Ants will be identified down to species in Dr. Mott’s lab following a set of identification keys. The data collected will be recorded and data analysis will be performed. Species richness, abundance, and evenness will also be calculated.

RESULTS & DISCUSSION

With this study, I expect to see a difference in biodiversity, richness and abundance between native vegetation and buffel grass. I expect a decrease of these in buffel grass. I also would like to analyze and compare the abundance and richness between native and non-native ants between native vegetation and buffel grass. This could bring insight on the effect buffel grass has on non-native species of ants and determine if it facilitates their settlement. If there is a difference in diversity more studies should be made on the impacts buffel grass has in the ecosystem to further understand the negative effects and determine management techniques.

CONCLUSION

Cenchrus ciliaris, buffel grass, is an invasive grass that can alter and cause negative effects to the ecosystems they invade. This study will provide insight to the effects this grass truly has on the environment and determine the ecological impact of buffel grass. This will be achieved by comparing ant biodiversity, richness and abundance in native vegetation and, buffel grass.  I expect the results of this study demonstrate a difference in ant diversity between native and non-native vegetation and that further studies can be made to determine buffel grass management.

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