Biosphere 2 Center

Exercise 14a: Ecological Impacts of a Single Introduced Ant Species
Module 14: Exotic Species Introduction

Introduction

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

Introduced species recently have become recognized as a 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). 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).

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.

The crazy ant, Paratrechina longicornis, occurs worldwide as both a tramp and an invasive ant species. Little is known about the basic biology of the crazy ant (Trager 1984). Its native habitat is thought to be West Africa (Creighton 1950), but its current worldwide distribution (Banks and Williams 1989; Farnsworth 1993; Wetterer 1998; Dejean et al. 2000) makes this difficult to ascertain. Crazy ants prefer moist conditions for reproduction but will nest anywhere (Trager 1984). They are quick to arrive at bait and then quick to recruit workers in high numbers, but they defer to more aggressive competitors when confronted (McGlynn 1999; Dejean et al. 2000). The more aggressive Solenopsis invicta has been observed to competitively displace P. longicornis, even though P. longicornis is much faster at arriving and using bait (Banks and Williams 1989). Crazy ants are known for their small size and ephemeral nests, and have been reported to be both monogynous (Yamauchi and Ogata 1995) and polygynous (Dejean et al. 2000). The ants tend homopterans for honeydew (Trager 1984), as well as scavenge dead insects.

The crazy ant is currently the ecologically dominant ant in the Biosphere 2 Center (B2C), North of Tucson, Arizona. The ants were accidentally introduced from an unknown source, but probably either via a soil core or in rootstock. Crazy ants were first documented inside B2C in 1993, two years after the first closure of the domes. As early as this first collection they were in high densities relative to the other five species present (Wetterer et al. 1999). By 1996, virtually all ants coming to bait were P. longicornis , which help to increase population sizes of the homopterans feeding on plants and producing honeydew. Later soil and litter surveys in 1997 (Wetterer et al. 1999) found an arthropod community skewed towards those species with physical defenses against ants (isopods, millipedes) or those able to escape ant predation (mites, thief ants, cockroaches), a characteristic fauna of areas invaded by dominant exotic ants ( Porter and Savignano 1990; Cole et al. 1992; Human and Gordon 1997; Wojcik et al. 2001).

Recent observations indicate that the crazy ants are not contained within the B2C domes (Danoff-Burg and Bahn unpub. data). The caulking between the glass panes of the B2C glass housing were initially tested and found to be termite-proof (Zabel 1996). However, the crazy ants became established after the termite test and are able to chew through the caulking, presumably also using the caulk for nest material (Zabel 1996). The holes provide a route through the glass and metal spaceframe housing of the B2C domes that the ants can use to forage for fluid and dead insects in the surrounding Arizona desert environment. The ants could then bring the solid and liquid material back to their nests inside the B2C domes. In the process, these ants could alter the amount of organic material in this otherwise materially closed environment, as well as the biochemical cycles occurring within it.

The current dominance of the crazy ant in the Biosphere 2 Center is a unique opportunity to study the effects of a single invasive/tramp species in an artificial, enclosed ecosystem. Our activity today aims to determine the impact of crazy ants on the B2C environment through the influx of solid and liquid nutrients foraged from the surrounding desert ecosystem. In particular, our goals are to estimate the annual nutrient influx into the Biosphere, soley as a consequence of crazy ant activity.

Lecture

1. Introduced or exotic species have been suggested to be involved in the extinction of over half of all species around the world!
• Competition
• Predation
• Introduction of parasites and other diseases
• Habitat alterations
• Disruption of native ecology
2. Species are introduced into nearly every possible environment, mostly due to human activity
• Deliberate introduction of desired species (crops, ornamentals, pollinators, biological control agents, fisheries, etc.)
• Accidental introduction of species (ballast water, plant movement, crop transportation, human movement, etc.)
3. Introduced species are most common in areas where humans conduct the greatest amount of trade or transportation of humans.
• These tend to be the centers of origin, from which introduced species radiate outwards to invade other areas
4. Population growth curves of introduced species differ from other species, generally growing exponentially. What are the two main population growth types and talk about when they would exist in nature (Draw each curve and label the X axis, Y axis, and the significant points in the curve)? 
• Exponential — unregulated growth, consistently exponentially increasing population size, apparently slow initially but rapid explosion eventually when growth is mapped out on the same graph 
• Occurs in nature when populations invade novel habitats or when food supply suddenly outstrips population size
• Difficult to naturally maintain, usually comes about as a consequence of environmental change 
5. Devising manners of controlling the reproduction and spread of these species is one of the greatest challenges facing conservation biologists, otherwise we could be implementing a gross homogenization of the Earth
6. Quick introduction to the basic biology of Paratrechina longicornis (see above)

Students will be asked at the end of the lecture to begin thinking of how to answer the question: "How could we determine the extent of the impact of crazy ants on nutrient cycling inside the Biosphere 2 domes?" Some relevant background information:

1. Crazy ants nest inside the domes, but forage for food outside of the domes in the surrounding desert
2. When they bring back food into the domes, they do so in both liquid and solid form 
3. Liquid food is brought back stored in their temporary stomachs (called a crop)
4. Solid food is carried back in their mouthparts (called mandibles) 

Objectives

1. Grasp that introductions of pest species by humans are one of the main contributors to habitat degradation.
2. Recognition that reductions in biodiversity and ecosystem processing accompany introduced species.
3. Basic understanding of some of the ways in which a single insect species could restructure an entire ecosystem through modifying nutrient flow.
4. Understanding of how to answer a question that does not have hypotheses.
5. Familiarity with the origins of measurement field error and how to minimize it.
6. Knowledge of some of the abiotic factors that influence ant activity.
7. Knowledge of basic biology of crazy ants including their scientific name.

Skills

1. Facility in devising methods to sample from a continuously flowing source of data (in this case, ant foraging activity) with minimal disruption to the organisms
2. Ability to standardize data collection across different environmental conditions
3. Be able to create confidence intervals
4. Skill in extrapolating data to other time intervals and across spatial scales
5. Be able to integrate data into a coherent story
6. Improved ability to present work orally via PowerPoint presentations

Methodology

• Possible Independent Variables: Time of day, Time of year, Temperature, Exposure (how sunny it is), Wind, Human Traffic, etc.
• Dependent variables: Solid Biomass and Liquid Biomass introduced into B2C
• After lecture, before the start of field time, the students will be asked to confer with their labmates and will be required to come up with a possible way to sample the amount of biomass flowing into B2C in a given period of time
• Best design that adequately answers the question will be that which we follow as a class
• Go to field and sample biomass data, first thing in the day – this will ideally start by 7 AM and finish by 10 AM.
• Return to lab
• Come up with nutrient flow estimates, confidence intervals, and estimations of the annual amounts of nutrient flow into the B2C. 
• Present the work as an oral report at the end of the day in the form of a PowerPoint presentation.

References

Banks, W.A. and D.F. Williams. 1989. Competitive displacement of Paratrechina longicornis (Latreille) (Hymonoptera: Formicidae) from baits by fire ants in Mato Grosso, Brazil. Journal of Entomological Science. 24(3): 381-391.

Burgess, T. L. 1995. Desert grassland, mixed shrub savanna, shrub steppe, or semidesert scrub?: The dilemma of coexisting growth forms. In: The Desert Grassland. Ed., M. P. McClaran and T. R. Van Devender. University of Arizona Press. Tucson, Arizona. 31-67.

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.

Farnsworth, E.J. 1993. Interactions between Cecropia peltata L. (Moraceae) and Paratrechina longicornis (Latreille)(Formicidae) at a sinkhole in the Guanica dry forest, Puerto Rico. Caribbean Journal of Science. 29(1-2): 124-125.

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

Hee, J.J., D.A. Holway, A.V. Suarez, & T.J. Case. 2000. Role of Propagule Size in the Success of Incipient Colonies of the Invasive Argentine Ant. Conservation Biology. 14(2): 559-563.

Holldobler, B. and E.O. Wilson. 1990. The Ants. Belknap Press of Harvard University Press. Cambridge, MA.

Holway, D.A. 1998. Factors governing rate of invasion: a natural experiment using Argentine ants. Oecologia. 115: 206-212.

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.

Kennedy, T.A. 1998. Patterns of an invasion by Argentine ants (Linepithema humile) in a riparian corridor and its effects on ant diversity. American Midland Naturalist. 140(2): 343-350.

McGlynn, T.P. 1999. Other ant invaders. TREE. 14(12): 489.

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.

Orr, M.R. and S. H. Seike. 1998. Parasitoids deter foraging by Argentine ants (Linepithema humile) in their native habitat in Brazil. Oecologia. 117: 420-425.

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.

Trager, J.C. 1984. A revision of the genus Paratrechina (Hymonoptera: Formicidae) of the continental United States. Sociobiology. 9(2): 49-162.

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.

Wetterer, J.K. 1998. Ants on Cecropia trees in urban San Jose, Costa Rica. Florida Entomologist. 81(1): 118.

Wetterer, J.K., S.E. Miller, D.E. Wheeler, et al. 1999. Ecological dominance by Paratrechina longicornis (Hymonoptera:Formicidae), an invasive tramp ant, in Biosphere 2. Florida Entomologist. 82(3):381-388.

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.

Yamauchi, K. and K. Ogata. 1995. Social structure and reproductive systems of tramp versus endemic ants (Hymonoptera:Formicidae) of the Ryukyu Islands. Pacific Science. 49(1): 55-68.