Ants in the GrasslandAnn B. MayoUniversity of Texas–ArlingtonAmerica’s Grassland ConferenceManhattan, KS

their importance and potential as indicators of ecosystem health

Why study ants?

• They bit and sting.• They may be pest and invasive species.• We do not invite them on picnics.

Fire ants (Solenopsis sp.) on an Oreo

Ants are quite fascinating and important.

Importance of Ants

• Ubiquitous • Diversity• Ecosystem engineers• Important relationships

Nest mound of the Western harvester ant

Internal nest of the Florida harvester ant

Potential as Bioindicators• Ecology and small scale• Ease of monitoring• Hypotheses

– Ground active ant assemblage will vary (and therefore, indicate)

– with habitat– with disturbance

• Comparison of ant assemblages in 17 sites– Fort Worth Nature Center, Fort Worth,

Texas

Tree trimming and mowing in an electrical power line right of way

17 Study Sites

• 3 wooded sites and 14 prairie sitesNatural experiment: sites were paired– same ecological unit/soil type• burned and unburned: 2 replicates• mowed and unmowed: 3 replicates• wooded and non-wooded: 3 replicates

Details of a Comanche harvester ant nest

Study Sites

burned site

oak woodland

mowed/disturbance site

mowed/disturbance site

mowed/disturbance site

Aquilla prairie

Aquilla prairie

Aquilla prairie Aledo clay loam

Methods• Environmental variables– soil characteristics– vegetation characteristics– ecological units

• Ant collection– pitfall traps in a 3 X 5 grid– 72 hour collection per month– March – September 2012

• Ordination Analysis in CANOCO• Functional Groups

Results: PCA

• Environmental variables

*** Summary of PCA for Environmental Variables ****Axes 1 2 3 4 Total

varianceEigenvalues 0.402 0.331 0.142 0.050 1.000Cumulative percentage variance of site data

40.2 73.3 87.5 92.5

Sum of all eigenvalues 1.000

PCA: Ecological Units

Aquilla prairie

Aquilla woodland

other sites

other sites

Results: RDA• Species occurrence and environmental variables

**** Summary of Full RDA with interaction term ****Axes 1 2 3 4 Total variance

Eigenvalues 0.158 0.120 0.100 0.084 1.000

Species-environment correlations 0.936 0.971 0.978 0.921

Cumulative percentage variance of species data

15.8 27.8 37.8 46.2

Cumulative percentage variance of species-environment relation

22.1 38.9 52.9 64.7

Sum of all eigenvalues 1.000Sum of all canonical eigenvalues 0.715

Significance of Effects SummaryMarginal EffectsVariable Lambda 1LiC*DRN 0.13LiCov 0.12DRN 0.12

Conditional EffectsVariable Lambda A P FLiC*DRN 0.13 0.001 2.17DRN 0.11 0.005 2.00LiCov 0.06 0.331 1.11

RDA: Sites and Variables

RDA: Species Occurrence

RDA: Species and Sites

Functional Groups• Dominant

Forelius (2)• Camponotini

Camponotus (2)• Hot Climate Specialists

Pogonomyrmex (2)Solenopsis (2 fire ants)

• Cold Climate SpecialistsPrenolepis (1)

• Cryptic SpeciesBrachymyrmex (2)Solenopsis (2 thief ants)Strumigenys (3)

• Opportunistic SpeciesAphaenogaster (2)Dorymyrmex (2)Nylanderia (2)

• Generalized MyrmicinaeCrematogaster (2)Formica (pallidefulva group - 1)Monomorium (1)Pheidole (4)Temnothorax (2)

• Specialist Predators -- none • Tropical Climate Specialists

Labidus (1)Trachymyrmex (2)

the Comanche harvester antharassed by Forelius

Functional Groups: site evaluation

Dom Camp Hot Cold Trop Opp GM Cryp0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

Frequency of Ant Functional Groups

Aquilla PrairieAquilla WoodlandOther

Functional Group

Freq

uenc

y

Conclusions

• Align with environmental, vegetation, and ecological characteristics.

• Potential as indicators of habitat types

• Potential as monitors of ecosystem health

the Comanche harvester ant foraging on seeds

Acknowledgements• Photo of Dr. Tschinkel (Florida State University)

and nest cast used with permission• Fort Worth Nature Center and Wildlife Refuge• City of Fort Worth, Texas

– Parks and Community Services Department

Questions Asked

• Are there implications for understanding/monitoring climate change?

Yes, this is one reason for studying ants – they are thermophilic in general and some species are found only in arid grasslands and deserts. As climate changes, the ant species present are expected to change in their occurrence, distribution and range. In the past, ants present in packrat middens have been used to asses or confirm climate conditions.

Questions Asked

• How are nest casts made?

Dr. Walter Tschinkel has especially developed techniques for making casts in wax, plaster, and aluminum. The chosen material is poured into a nest, allowed to harden, and then excavated. Visit his site at Florida State University for more information. He has several papers on nest casts and architecture.

Questions Asked

• What does low intensity fire mean?

The prairies that were burned were controlled, low intensity burns meant to control scrubby woody growth and reduce litter. Intensity of a burn has to do with how hot and how long. These burns did not significantly effect the soil. For ants, this means that only the microclimate above ground was affected which can be a significant deterrent to ant activity and presence. I did not detect such an effect in this study.