Nurse plants and ecosystem engineering in semi-arid environments

In semi arid env, water and nutrients are limiting.

tree and shrubs scattered sparsely across the landscape drive the availabilityof such resources. they are called nurse plants

they provide shade, cooler temps, stable humidty, UV protection, protect from herbivores and abiotic forces.

as a result, the availability of rare resources is concentrated underneath their canopies. these effects can then facilitate the establishment and survival of interspecifics undernetah them.

Abiotic objects such as rocks, logs and animal diggings have also been recognised as Nurses although they have been given very little attention.

therefore they are critical components generating ecosystem structure and productivity.

nurse objects created by other organisms (i.e. diggings and logs) have the potential to 'engineer' the environment; that is modifying or creating resources for other species ('ecosystem engineers')

this study, investigated how male great bowerbirds may be driving the availbility of rare resources in semi-arid savannah of Australia and if they may be engineering their environment through unique means.

great bowerbirds build a bower to attract and mate with females.

surrounding the avenue is a collection of 'ornaments' such as bark, dung, bones, and fruits which the male waves at females to impress her.

after the breeding season, the bower is abandoned. the ornaments remain and the whole bower gradually decomposes over several years.

Given that great bowerbirds construct a structure of organic material and they are exclusively located underneath shrub canopies, the effect of the bower on the soil may augment the pre-existing nurse effect of shrubs thereby providing such unique conditions that could allow range expansion of less tolerant species, enabling them to survive in environments far beyond their physiological tolerances

In addition, soil enhancement could facilitate other species previously not considered in this context, i.e. fungi and bacteria, potentially further facilitating plant establishment. Furthermore, secondary effects on other species would reveal the bowerbirds as ecosystem engineers

Aim: investigate the effects of bower building and site selection by male great bowerbirds on the nutrient and moisture properties of soils underneath the dominant shrub species Carissa ovata.

Hypothesis:

1. Great Bowerbird bowers modify the moisture, nutrient and chemical properties of the soil.

soil samples taken from

1. shrubs with an abandoned bower (BS)

2. random selected shrubs (RS)

3. canopy controlled shrubs (shrubs with equal canopy cover to bower shrubs (CCS)

4. 1.5 m away from abandoned bower but underneath the same canopy (adjacent control (AC)

Microhabitat variables measured were canopy cover, temperature and relative humidity

Properties tested on the soil were;

N, P, K, Mg, C, Na, Ca, pH, h2o and CEC (sum of K, Mg, Ca and Na)

METHODS

INTRODUCTION