# ants

##### Harkness-Isham ants' nests data

These data give the spatial locations of nests of two species of
ants, *Messor wasmanni* and *Cataglyphis bicolor*,
recorded by Professor R.D. Harkness at a site in northern Greece,
and described in Harkness \& Isham (1983).
The full dataset (supplied here) has an irregular polygonal boundary,
while most analyses have been confined to two rectangular
subsets of the pattern (also supplied here).

The harvester ant *M. wasmanni*
collects seeds for food and builds a nest composed mainly of
seed husks. *C. bicolor* is a heat-tolerant desert foraging ant which
eats dead insects and other arthropods. Interest focuses on whether
there is evidence in the data for intra-species competition
between *Messor* nests (i.e. competition for resources) and for
preferential placement of *Cataglyphis* nests in the vicinity of
*Messor* nests.

The full dataset is displayed in Figure 1 of Harkness \& Isham (1983).
See **Usage** below to produce a comparable plot.
It comprises 97 nests (68 Messor and 29 Cataglyphis)
inside an irregular convex polygonal boundary, together with
annotations showing a foot track through the region,
the boundary between field and scrub areas inside the
region, and indicating the two rectangular subregions
A and B used in their analysis.

Rectangular subsets of the data were analysed by Harkness \& Isham (1983), Isham (1984), Takacs \& Fiksel (1986), S\"arkk\"a (1993, section 5.3), H\"ogmander and S\"arkk\"a (1999) and Baddeley \& Turner (2000). The full dataset (inside its irregular boundary) was first analysed by Baddeley \& Turner (2005b).

The dataset `ants`

is the full point pattern
enclosed by the irregular polygonal boundary.
The \(x\) and \(y\) coordinates are eastings (E-W) and northings (N-S)
scaled so that 1 unit equals 0.5 feet.
This is a multitype point pattern object, each point carrying a mark
indicating the ant species (with levels `Cataglyphis`

and `Messor`

).

The dataset `ants.extra`

is a list of auxiliary
information:

`A`

and`B`

The subsets of the pattern within the rectangles A and B demarcated in Figure 1 of Harkness \& Isham (1983). These are multitype point pattern objects.

`trackNE`

and`trackSW`

coordinates of two straight lines bounding the foot track.

`fieldscrub`

The endpoints of a straight line separating the regions of `field' and `scrub': scrub to the North and field to the South.

`side`

A

`function(x,y)`

that determines whether the location`(x,y)`

is in the scrub or the field. The function can be applied to numeric vectors`x`

and`y`

, and returns a factor with levels`"scrub"`

and`"field"`

. This function is useful as a spatial covariate.`plotit`

A function which produces a plot of the full dataset.

##### Usage

`data(ants)`

##### Format

`ants`

is an object of class `"ppp"`

representing the full point pattern of ants' nests.
See `ppp.object`

for details of the format.
The coordinates are scaled so that 1 unit equals 0.5 feet.
The points are marked by species (with levels `Cataglyphis`

and `Messor`

).

`ants.extra`

is a list with entries

- A
point pattern of class

`"ppp"`

- B
point pattern of class

`"ppp"`

- trackNE
data in format

`list(x=numeric(2),y=numeric(2))`

giving the two endpoints of line markings- trackSW
data in format

`list(x=numeric(2),y=numeric(2))`

giving the two endpoints of line markings- fieldscrub
data in format

`list(x=numeric(2),y=numeric(2))`

giving the two endpoints of line markings- side
Function with arguments

`x,y`

- plotit
Function

##### References

Baddeley, A. and Turner, R. (2000)
Practical maximum pseudolikelihood for spatial point patterns.
*Australian and New Zealand Journal of Statistics*
**42**, 283--322.

Baddeley, A. and Turner, R. (2005a)
Spatstat: an R package for analyzing spatial point patterns.
*Journal of Statistical Software* **12**:6, 1--42.
URL: `www.jstatsoft.org`

, ISSN: 1548-7660.

Baddeley, A. and Turner, R. (2005b)
Modelling spatial point patterns in R.
In: A. Baddeley, P. Gregori, J. Mateu, R. Stoica, and D. Stoyan,
editors, *Case Studies in Spatial Point Pattern Modelling*,
Lecture Notes in Statistics number 185. Pages 23--74.
Springer-Verlag, New York, 2006.
ISBN: 0-387-28311-0.

Harkness, R.D. and Isham, V. (1983)
A bivariate spatial point pattern of ants' nests.
*Applied Statistics* **32**, 293--303.

Hogmander, H. and
Sarkka, A. (1999)
Multitype spatial point patterns with hierarchical interactions.
*Biometrics* **55**, 1051--1058.

Isham, V.S. (1984)
Multitype Markov point processes: some approximations.
*Proceedings of the Royal Society of London, Series A*,
**391**, 39--53.

Takacs, R. and Fiksel, T. (1986)
Interaction pair-potentials for a system of ants' nests.
*Biometrical Journal* **28**, 1007--1013.

Sarkka, A. (1993)
*Pseudo-likelihood approach for pair potential
estimation of Gibbs processes*.
Number 22 in Jyvaskyla
Studies in Computer Science, Economics and Statistics.
University of Jyvaskyla, Finland.

##### Examples

```
# NOT RUN {
# Equivalent to Figure 1 of Harkness and Isham (1983)
data(ants)
ants.extra$plotit()
# Data in subrectangle A, rotated
# Approximate data used by Sarkka (1993)
angle <- atan(diff(ants.extra$fieldscrub$y)/diff(ants.extra$fieldscrub$x))
plot(rotate(ants.extra$A, -angle))
# Approximate window used by Takacs and Fiksel (1986)
tfwindow <- boundingbox(Window(ants))
antsTF <- ppp(ants$x, ants$y, window=tfwindow)
plot(antsTF)
# }
```

*Documentation reproduced from package spatstat, version 1.52-1, License: GPL (>= 2)*