Atlantic Forest

Background

(Reference citations are included at the bottom of the webpage)

Introduced species recently have become recognized as a significant threat to the diversity of native ecosystems worldwide, leading to an increase of interest in invasion biology and theory (Enserink 1999). Alien species are second only to habitat destruction and degradation in extirpating species from their native habitats (Vitousek 1996; Enserink 1999).

The branch of ecology studying introduced species is a new one that has achieved enhanced recognition of late. Much of the increase in prominence is due to several recent high-profile species introductions (zebra mussel, green crab, Asian longhorned beetle, the West Nile Virus, and purple loosestrife in the continental United States) and the enhanced theoretical rigor of the field.

These introduced species are leading to a dramatic restructuring of ecoystems around the world and to the extinction of thousands of species. Partly as a recognition of the importance and rapid development of this field, Science magazine recently had a special issue reviewing the problem (Vol. 285, No. 5435). Successful invaders can significantly restructure ecosystems when they are most influential, in the process altering several key ecosystem functions and thus the ecosystem itself (Cox 1999).

Most of these species were introduced into novel areas due to human activity. Because human mobility and shipping have increased, the number of accidentally introduced species around the world has reached a fever pitch and continues to escalate. Introduced species are also intentionally introduced as biological control agents and for erosion control, farming, and sport fishing.

Irrespective of the mode of introduction, these species can and have become serious pest species, leading to millions of dollars of economic impact and untold damage to the local ecological balance. Governmental and private funding for basic and applied research on exotic species and permanent research positions focusing exclusively on exotics have each proliferated worldwide. The field of invasion biology will only continue to become more prominent as additional human-facilitated species introductions continue.

Intentional introductions of exotic plants can transform the ecosystem into a completely non-native agglomeration of introduced species. This is particularly notable for tree species that are planted in dense monospecific aggregations, such as the eucalyptus throughout this area of Brazil. Native species often cannot cope with the sudden infusion of many individuals of an exotic species. The native plants are often out-competed for nutrients and shade. The native animals often cannot cope with the anti-herbivory and defensive secondary chemicals that the exotic plant species may have. Once the native herbivores are lost, native predators, parasites, and often decomposers also vanish. As a consequence native species often cannot live in these dense stands of exotics and are locally lost (extirpated) from the area.

As is often stated, nature abhors a vacuum, and even those ecosystems comprised of exotic species are no exception. The stand of exotic trees is a resource waiting that will be exploited by some set of species. Consequently, these heavily altered ecosystems often predispose the ecosystem for further invasions by exotic species. Exotic species are often very hardy and can live in a great diversity of ecosystems, including novel environments such as exotic species monocultures.

Invasive social insects and ants in particular are among the most influential of introduced species (Human and Gordon 1997). The argentine ant, Linepithema humile, the red imported fire ant, Solenopsis invicta, and the big-headed ant, Pheidole megacephala are all extremely successful invasive ant species in the United States. These ants have lowered diversity of species and functional roles in native arthropod and vertebrate communities (Porter and Savignano 1990; Cole et al. 1992; Dejean et al. 2000; Huxel 2000; Vanderwoude et al. 2000; Wojcik et al. 2001).

The species and functional roles that have been lost can significantly affect other animals and plants that rely on the ecosystem services provided by the native animals. Soil turnover, pollination efficiency, and loss of other key relationships that can restructure the local ecosystem may all result from the loss of native species. Additionally, the arthropod communities that remain after successful ant invasions are often skewed toward those insects that live underground, such as mites, or those that have hard exoskeletons, such as isopods and cockroaches (Porter and Savignano 1990; Cole et al. 1992; Human and Gordon 1997; Wojcik et al. 2001). Highly influential exotic ants could also alter nutrient flow and biomass cycling, through both their own activity and by excluding other species and thereby ending their ecological impact.

Social insects have the capacity to be highly successful colonizers due to their potential flexibility at both the individual and colony level. In some species workers can forage individually or cooperatively according to which is more efficient (Moller 1996; Morrison 2000). Worker size polymorphisms can vary to adapt to changing conditions (Moller 1996; Morrison 2000). Conspecific colonies often suppress territoriality, particularly in those species that are facultatively polygynous "supercolonies" (Moller 1996; Holway et al. 1998; Suarez et al. 1999; Tsutsui et al. 2000; Wojcik et al. 2001). Facultatively polygynous species such as S. invicta are able to have colonies that are twice or three times as dense as conspecific solitary colonies. These benefits may make social insects especially effective when in competition with other non-social native arthropod species (Moller 1996).

When their unique traits are combined with those that are frequently found in other successful exotics (e.g., quick and massive reproduction, preferring disturbed habitats, and competitive release), ants become super exotics capable of invading or colonizing many novel habitats (Holway et al. 1998; Feener 2000; Morrison 2000). Most successful invasive ant species are quick to recruit to bait, able to nest in different types of areas, able to raid interspecific nests, and able to thrive in disturbed areas (McGlynn 1999). They excel in aggressively garnering disproportionately large amounts of resources, relative to local species. Additionally, not all successful exotic ant species are aggressive invaders. Tramp ants may often occupy niches not filled by native ants, such as urban environments.

Today, we will analyze to what extent a monoculture of eucalyptus trees has on the biodiversity in the area. You have the opportunity to choose the organisms that you wish to study and the specific question that you wish to answer. A few possible starting points are given in the questions above.

Your Assignment

This assignment involves completing four tasks.

• Design of field experiment (1 hr, day before activity)
• Data collection for field experiment (3 hrs)
• Data analysis and write-up (1.5 hrs)
• Presentation (0.5 hr)

To complete these tasks, you should proceed through the following steps. First, you and your lab group should design a field experiment that would test some aspect of the effect of eucalyptus monocultures have on the biodiversity of communities. Some possible applications of the above main questions that your group could address include the following:

1. Setting aside the question of the affect of the plants on other species, are there ecological correlates that can be used to predict the probability of establishment of freely propagating eucalyptus stands?
2. Do eucalyptus affect the community diversity of plants and insects living nearby in areas where there are fewer trees relative to others where they are in a monoculture?
3. Do the eucalyptus trees most strongly affect those species with which they directly interact relative to others in the community?
4. Another question of your own design that is related to one of the main questions.

Be certain to control for environmental differences, including moisture, topography, sunlight, temperature, slope orientation, etc., when determining which sites are appropriate to compare.

Include another type of forest to compare with the eucalyptus monoculture. What is the best forest to use for this study? A climax Atlantic Forest? A forest of the same age as the monoculture? A forest of the same canopy size as the monoculture, irrespective of the age of the trees in it? Be able to justify your answers.

Third, you should collect the data that you will need for your study, analyze it, and then present it before late afternoon.

You will have to finish all of this assignment today. As with previous activities, the quality of the data from the field experiment and the rapidity with which you are able to complete the task both will be enhanced if multiple lab pairs cooperate to collect data for the same study. The day before we do the activity, ask around to other groups to find others who are interested in addressing similar questions. Also as with previous activities, you will be graded not only on your experimental design, execution, and outcome, but also on how well you work together and on the final oral presentation.

Objectives

1. Grasp that accidental introductions of pest species by humans are one of the main contributors to habitat degradation.
2. Recognition that reductions in biodiversity and ecosystem processing often accompany the introduction of exotic species.
3. Basic understanding of how insect pest species spread and interact with other ecological community members.
4. Knowledge of the basic biology and ecology of the eucalyptus tree species we have locally, where they live, and the species with which they directly interact, including scientific names.
5. Improved grasp of scientific methodology principles.
6. Improved understanding how to create a set of hypotheses to test a question.
7. Familiarity with the origins of measurement error and how to minimize it.

Key Skills

1. Facility in conducting animal or plant community surveys.
2. Familiarity with how to conduct a systematic survey for a single species.
3. Skill in interpreting ecological correlates included in georeferenced community survey data.
4. Ability to estimate community diversity indices.
5. Dexterity in comparing diversity indices between sites and ecological conditions.
6. Skill at designing equal sampling efforts between heterogeneous sites.
7. Improved ability to present work orally.
8. Greater facility with GPS and GIS data processing.

Timetable

1. Total elapsed time to perform the experiment : One day
   • Design of field experiment, implementation of field experiment, insect censusing, mapping, statistical analyses, write-up and oral presentation should all be done in one day
2. Total elapsed hands-on time: approximately Six hours
   • Design of field experiment (1 hr, day before activity)
   • Data collection for field experiment (3 hrs)
   • Data analysis and write-up (1.5 hrs)
   • Presentation (0.5 hr)

Procedural Notes

1. The degree to which students in the class collaborate will determine which question they should be encouraged to answer
   • If the entire class is interested in one of the Community Diversity questions, then it would be possible to answer that question. The methodology outlined above is very time consuming and would require a large work effort—this is too much work for a small group
   • However, if only a subset of the class is interested in the Community Diversity questions then one group should be encouraged to answer the Ecological Correlates question and another group could answer another question of their own design.

Materials Needed

1. GPS units
2. Insect collecting equipment—determined by students
3. Plant presses and leaf baggies
4. Clipboards & paper or notebooks, and writing implements
5. Soil moisture and texture evaluation methods and equipment
6. Slope measuring tool (two yardsticks attached at end with a level on one and a protractor)
7. Thermometer
8. Dissecting microscopes
9. Sorting trays, forceps, alcohol
10. Computer with Excel, Word, SPSS, and eBiome loaded

References

Cohen, J.E. and D. Tilman. 1996. Biosphere 2 and biodiversity: the lessons so far. Science. 274(5290): 1150-1151.

Cole, F.R., A.C. Medeiros, L.L. Loope, and W.W. Zuehlke. 1992. Effects of the Argentine ant on arthropod fauna of Hawaiian high-elevation shrubland. Ecology. 73(4): 1313-1322.

Dejean, A., J. Orivel, J.L. Durand, et al. 2000. Interference between ant species distribution in different habitats and the density of maize pest. Sociobiology. 35(1):175-189.

Enserink, M. 1999. Biological invaders sweep in. Science. 285(5435): 1834-1836.

Feener, D.H., Jr. 2000. Is the assembly of ant communities mediated by parasitoids? Oikos. 90: 79-88.

Holway, D.A., A.V. Suarez, and T.J. Case. 1998. Loss of intraspecific aggression in the success of a widespread invasive social insect. Science. 282(5390): 949-952.

Human, K.H. and D.M. Gordon. 1997. Effect of argentine ants on invertebrate biodiversity in northern California. Conservation Biology. 11(5): 1242-1248.

Huxel, G.R. 2000. The effect of the Argentine ant on the threated elderberry longhorn beetle. Biological Invasions. 2: 81-85.

McGlynn, T.P. 1999. The worldwide transfer of ants: geographical distribution and ecological invasions. Journal of Biogeography. 26(3): 535-548.

Moller, H. 1996. Lessons for invasion theory from social insects. Biological Conservation. 78:125-142.

Morrison, L.W. 2000. Mechanisms of interspecific competition among an invasive and two native fire ants. Oikos. 90: 238-252.

Porter, S.D., and D.A. Savignano. 1990. Invasion of Polygyne Fire Ants Decimates Native Ants and Disrupts Arthropod Community. Ecology. 71(6): 2095-2106.

Suarez, A.V., N.D. Tsutsui, D.A. Holway, & T.J. Case. 1999. Behavioral and genetic differentiation between native and introduced populations of the Argentine ant. Biological Invasions. 1: 43-53.

Tsutsui, N.D., A.V. Suarez, D.A. Holway, T.J. Case. 2000. Reduced genetic variation and the success of an invasive species. Proceedings of the National Academy of Science. 97(11): 5948-5953.

Vanderwoude, C., L.A. Lobry de Bruyn, & A.P.N. House. 2000. Response of an open-forest ant community to invasion by the introduced ant, Pheidole megacephala. Austral Ecology. 25: 253-259.

Vitousek, P.M, C.M. D'Antonio, L.L. Loope, and R. Westbrooks. 1996. Biological invasions as global environmental change. American Scientist. 84: 468-478.

Wocjik, D.P., C.R. Allen, R.J. Brenner, E.A. Forys, D.P. Jouvenaz, and R.S. Lutz. 2001. Red imported fire ants: impact on biodiversity. American Entomologist. 47(1): 16-23.