FORAGING AND RECHUITMENT ABILITIES OF SOLENOPSIS INVICTA BOREN, CO*!PARED WITH OTHER ANT SPECIES INDIGENOUS TO TEXAS by STANLEY R. JONES, B.S. A THESIS IN ENTOMOLOGY Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE Approved May, 1985 yv C-C^^'^ ACKN0^LEDGE?1ENTS I would like to express my sincere appreciation to Dr. Sherman Phillips, committee chairman, for his guidance and support of this research. To Dr. Bernard Hartaan and Dr. James Wangberg I extend my gratitude for serving as commit­ tee members and for review of this thesis. I ar^ grateful to Dr. a. Willig for his helpful comments and assistance with data analysis, to Dr. Oscar Francke for verification of ant species identification, and to Is. Mary Peek for technical assistance. Finally, I thank James Cok- endolpher for review of preliminary drafts of this thesis. Special recognition is given to my parents for their encouragement and support of my education. To my wife Jo Ann, I express r^y deepest appreciation for her understand­ ing, support, and consideration during my graduate studies. This research was conducted through the facilities and financial resources provided by '^exas Tech University. To this institution I aii indebted. 11 ABSTRACT Since its accidental introduction into "•obile, Alabama, the red imported fire ant, Solenopsis invlcta Buren, has be­ come an economic pest of much of the southern United States. Each year this ant continues to expand its range. Why S. invicta is able to successfully colonize areas previously inhabited by multifarious ant species is not understood. Possible explanations include its aggressive behavior, large colony size, and foraging efficiency. This study was con­ ducted to compare the foraging efficiency of S. invicta to three ant species native to south central Texas. Native ants studied include Pheidole dentata Mayr, wonomorium mini­ mum (Buckley) , and Forelius foetid us (Buckley) . Temporal recruitment and food retrieval patterns were recorded and con^pared for all four species held at equal colony strengths. Results indicate that interspecific differences in recruitment patterns do occur. However, these differenc- 9.5 are subtle and do not suggest that S. invicta is a more efficient forager under laboratory conditions, than the oth­ er three species. Ill TABLE OF CONTENT'S ACK>:OWLEDGEME!yTS 11 ABSTRACT 111 LIST OF TABLES iv LIST OF FIGUPES V CHAPTER I. INTPODUC^ION AND LITERATURE REVIEW 1 Foraging and Pecruitment 5 Aggression 21 Competitive Avoidance 24 Objectives 31 General .Species biology 32 Pheidole dentata 32 Solenopsis invicta 32 Forelius foetidus 3 3 Monomorium minimum 3U II. r^STIIODS AND MATERIALS 36 Confrontation 37 Aggressive Ability 37 Defensive Ability 38 Recruitment and Foraging 39 Distance Travelled and Turns "Executed 44 Recruitment 47 Paits 48 Foraging 51 III. PiSUL'^:^ 53 Confrontation 53 Aggressive Ability 53 Defensive Ability 58 Recruitment and Foraging 61 Distance Travelled and Turns Executed 61 Pecruitment 63 Foraging 67 IV IV. DISCUSSION 71 LIT^RATUFE CITED 87 APPENDIX A. ANALYSIS OF VARIANCE TABLES FOR FLFVEN PARA'IETERS 94 LIST OF TABLES 1. Analysis of variance table for number of contacts made by 17 species-caste combinations 94 2. Nested analysis of variance table for distance travelled 94 3. Nested analysis of variance table for number of turns executed 95 4. Nested analysis of variance table for initiation of recruitment 95 5. Nested analysis of variance table for time to reach peak numbers 96 6. 'tested analysis of variance table for peak numbers recruited 96 7. Nested analysis of variance table for bait retrieval time 97 ^. Nested analysis of variance table for numbers foraging prior to bait placement 97 9. Nested analysis of variance table for time required to discover a bait following placement 98 10. Nested analysis of variance table for numbers foraging after bait retrieval 98 11. Nested analysis of variance table for time to retrieve single baits 99 VI LIST OF FIGURES 1. Top ard side view (with detail) of a single ant foraging tray/myrmicary container 4 0 2. Side view of a free water dispenser, constructed from ^0X20 mm petri dishes 43 3. Top view of single ant foraging tray/myrmicary container 45 4. Results of confrontation studies between four ant species for 17 species-caste combinations 54 5. Results of confrontation studies between four ant species 57 6. Comparison of defensive abilities between 17 species-caste combinations 5 9 7. Comparison between species for distance travelled and number of turns executed 62 8. Comparative recruitment patterns of fotir ant species 64 9. Peak numbers recruited to food baits and bait retrieval times for four ant species 65 10. A comparison between species for the number of ants foraging prior to bait placement and after bai^ retrieval 68 11. A comparison between species for the time required to retrieve single baits 22 cm 69 vii CHAPTFIR I INTRODUCTION AND LITERATURE REVIEW The manner in which various biotic and abiotic factors interplay in the environment determines not only the diver­ sity of an ecosystem, but also the particular habitats and functions of the taxa involved (Odum, 1975). Widely differ­ ing taxa, or similar taxa which utilize different resources, may have widely overlapping ranges with little or no effect on each other. Conversely, similar or dissimilar taxa with similar abiotic and/or biotic requirements may interact in various ways leading to resource partitioning (Wilson, 1971). Thus, organisms in an ecosystem occupy more or less well defined areas or niches. The niche concept has been variously defined by such early authors as Grinnell (1924), and Elton (1927) . In 1957, Hutchinson defined niche in a more complex but perhaps more accurate manner. His niche concept, known as a multi­ dimensional hypervolume, accounts for all environmental variables important to an organisms survival, and defines the organism's fundamental niche. Hutchinson further refined the concept to include an organism's realized niche which is the portion of the fundamental niche actually occupied by an organism after interactions with other organisms are accounted for. In this paper, Hutchinson's definition of niche will be assumed. Ants are conspicuous by their numbers and typically play a prominent role in most terrestrial habitats. Ants are generally among the principal predators of other in­ vertebrates. Their consumption of biomass and energy ex­ ceeds that of vertebrates in most terrestrial habitats. This large accumulation of biotic material is achieved via the continual searching of foragers night and day (Wilson, 1971) . because ants are so prominent in terrestrial habitats, inter- and intraspecific interactions are common and are im­ portant in shaping the distribution of ant species in a com­ munity, other biotic and abiotic factors are also important and include vegetation type and cover, food abundance, dis­ persion and dependability, temperature, rainfall and soil type (Sherba, 1<364) . With respect to food utilization, most ant species are omnivorous (Carroll and Janzen, 1973). Even predacious ants which utilize mobile insects as prey, sup­ plement their diet with scavenged resources. This behavior is due in part to the variable location in time and space of mobile prey, as well as the large energy expenditure required to locate and capture these items (Carroll and Janzen, 1973). Omnivorous food habits are usually correlated with broad niches and low food availability. Niche breadth for any one population should increase as a result o^ selection acting through the resource in short supply C^ernstein, 1979). Species diversity may also be re­ duced by lowered resource availability (Bernstein, 1979). For example, ant colonies are often more widely spaced in areas of low productivity than in areas of high productivi­ ty, with a corresponding reduction in diversity. This cir­ cumstance was described by Davidson (1977) for several spec­ ies of granivorous ants. This relationship indicates that food is probably a limiting resource (Davidson, 1977). Species diversity within a community may also depend on moisture gradients and general environmental heterogeniety (Davidson, 1977). Bernstein (1979) identified three compo­ nents of environmental heterogeniety which are important when considering niche breadth in ants. These factors in­ clude: the range of temperatures utilized for foraging, the size of the foraging area, and the diversity in size and distribution of food sources utilized. 7hen environmental conditions favor an increase in niche breadth, indicated by low species diversity and omnivorous food habits, populations may respond with an increase in either the within phenotype component or the between phenotype component of niche breadth. The between phenotype component is shaped by the above ecological factors and is expressed as differences among individuals within a population. In the extreme case, these ecological factors could lead to a population composed of individuals highly specialized for individual tasks. This condition is unlikely because the diversity of genes within a population limits the phenotypic variability, and genetic recombination tends to dilute high­ ly specialized genotypes (Bernstein, 1979). The within phe­ notype component of niche breadth involves the variety of resources collected and used by each individual within a population. In the extreme case, the population would be totally composed of generalists, each of whose niche breadth would equal that of the population as a whole. A population of this type would be highly inefficient in resource utili­ zation (Pernstein, 1979). However, in areas of low food availability, populations will tend to be generalists in or­ der to secure as much of the available resources as possi­ ble. Ants, due to their social behavior, have been able to increase the efficiency of resource utilization despite an increase in the within-phenotype component of niche breadth (Bernstein, 1979). In ant communities, a gradation of generalists (within-phenotype component) to specialists (between-phenotype component) can be found.