Sparganophilus pearsei

## Source: ResearchGate

ABSTRACT

A correlation analysis of quantitative data collected from

71 sites in the Haliburton Highlands was presented. The

effects of numerous abiotic and biotic factors on megadrile

activity in the soil, which have universal application, were

demonstrated. A flow-diagram model illustrates these habitat

interactions on earthworm activity.

UN MODELE CONCEPTUEL PRELIMINAIRE DE

L'ACTIVITE ET DE L'ABONDANCE DES

LOMBRICIDES AUX HIGHLANDS

D'HALIBURTON, ONTARIO

Une analyse de correlation a ete presentee sur les donnees

quantitative recueillies de 71 stations aux Haliburton High-

lands. Les effets de beaucoup de facteurs abiotiques et

biotiques sur l'activite des lombricides dans le sol, d'application

universelle, y sont dernontres. Un "flow-diagram" mod ele

ilIustre ces interactions d'habitat sur l'activite des lombricides.

EIN VORLAUFIGES, SCHEMATISCHES MODEL

FUR REGENWURMT ATIGKEIT UND

HAUFIGKEIT IM HALIBURTONISCHEN

BERGLAND VON ONTARIO

Der Artikel enthalt das Ergebnis einer Korrelationsanalyse.

von quantitativen Daten, die durch Untersuchungen an 71

verschiedenen Standorten im haliburtichen Bergland von Ontario

erhalten wurden. Die Wirkung auf die Regenwurrntatigkeit von

zahlreichen biotischen und abiotischen Factoren, die von uni-

verseller Bedeuting sind, wurde aufgezeigt. Diese Wechselwir-

kungen im Regenwurmhabitat sind in schematischer Darstellung

ilIustriert.

"TallTimbersResearchStation,Tallahassee,Florida,USA,32303.

'Faculty of Forestry, Universityof New Brunswick, Fredericton,New

Brunswick,Canada,E3B 5A3.

INTRODUCTION

A study of the earthworms (megadriles) from 71 sites in

Haliburton County, Ontario, including detailed habitat information

was presented in a previous paper (Reynolds, 1972a). One

objective of that initial study was to expand the habitat data

normally recorded in order to later evaluate its possible effects

on megadrile activity and distribution. Requests for such

additional data have been heard from oligochaetologists the

world over (Bouche , 1972; Gates, 1972, Ljungstrorn, 1970;

and Reynolds, 1972b and 1973a) but will also be useful to

biogeographers and ecologists.

As a result of that initial paper we will now attempt to

determine which habitat factors controlled earthworm distribution

and activity and to model their interactions. In addition to

date, location and name of col!ector(s), ten habitat factors

(variables) were recorded,

viz.

slope, aspect, elevation, physio-

graphic position, soil reaction, soil temperature, soil moisture,

soil colour, soil texture and vegetation (nutrient source).

To the best of our knowledge, slope, aspect and soil

colour have not previously been considered as factors affecting

earthworm activity. Elevation and physiographic position in

relation to earthworm distribution were discussed by Reynolds

(1971 and 1973). Soil reaction has received considerable atten-

tion (Evans and Guild, 1947; Lee, 1959, 0lson, 1928; Reynolds,

1971 and 1972c; Satchel!, 1967; and Wherry, 1924). The

effects of temperature have been discussed by Grant (1955b),

Kollmannsperger (1955), Michon (1954) and Reynolds (1972c)

while soil moisture has been discussed by Evans and Guild

(1947), Olson (1928), and Reynolds (1973a). Soil texture appar-

ently has been handled only by Guild (1948), and the influence

of vegetation and palatability studies presented by Edwards and

Heath (1963), Heath

et al.

(1966) and Reynolds (1972b and

1973a).

METHODS AND RESULTS

Data for the ten variables recorded at each site

(vide,

Reynolds, 1972a) were coded for purposes of computer assisted

analysis as follows:

1. Slope - degrees

(0)

from the horizontal.

2. Aspect - degrees

(0)

from north (azimuth) where north

=

O.

3. Elevation - meters (m) above sea level.

4. Physiographic Position - subjectively coded, where 1

bottomland, 2

=

terrace, and 3

=

upland.

2

A Preliminary Conceptual Model of Megadrile Activity

5. Soil Reaction or H+ concentration - pH values

(vide

Black, 1968; p. 273-355).

6. Soil Temperature - in degrees Celcius

("C).

7. Soil Moisture - subjectively coded, where 1 = dry,

2 = dry-moist, 3= moist-dry, 4 = moist,

5

= moist-wet,

6 = wet-moist, and 7 = wet.

Soil Colour - Munsell notation (Hue, Value, Chroma).

(vide

Munsell, 1954; USDA, 1951).

9. Soil Texture - per cent of soil separates.

Vegetation - subjectively coded based on palatability scale.

where

0

=

Robinia,

2

=

Populus,

4 =

Acer, Salix, Ulmus,

Rhus, Pr un us,

5

=

Liriodendron,

6

=

Betula, Fraxinus,

Gleditsia, Tilia,

8 =

Fagus, Q'uercus,

9 = conifers.

Alterations to the original data are found in the Appendix.

Data were punched on computer cards and a correlation

analysis performed, employing a computer program initially

prepared by Kozak (1970) and modified for the IBM/370-158

at the University of New Brunswick. Results are summarized

in Tables

1

and 2.

Table 1. Elementary Statistics for Haliburton Earthworm

Data (n

=

71).

Factor Mean Standard Minimum Maximum Coefficient

Deviation of Variation

Juvenile

2.658 3.468 0 17.000 130.49

Aclitellate

0.757 1.658 014.000 219.11

Adult

Clitellate

1.387 2.487 0 13.000 179.25

Adult

Postclitellate

0.171 0.537 0 3.000 313.86

Adult

Total

4.964 6.227 1.000 34.000 125.45

Earthworms

Slope

6.631 6.075 0 30.000 91.62

Aspect

156.811 117.849 0 360.000 75.15

Elevation

872.466 105.515 685.160 1122.580 12.09

Physiographic

2.054 0.749 1.000 3.000 36.45

Position

pH

5.592 0.718 3.900 7.200 12.83

Temperature

16.820 1.960 14.000 22.000 11.64

Moisture

3.126 1.322 1.000 7.000 42.29

Hue

9.865 0.568 7.500 10.000 5.76

Value

4,324 0.811 2.000 6.000 18.75

Chroma

2,946 0.989 0 6.000 33.58

% Sand

36.685 28.458 5.000 90.000 77.58

%

Silt

33.450 21.375 5.000 70.000 63.90

% Clay

20.343 13.746 5.000 45.000 67.57

%O.M.

5.117 16.289 0 85.000 318.33

% Gravel

4.748 11.896 050.000 250.56

Vegetation

4.333 1.855 2.000 9.000 43.04

DISCUSSION

Many ecological factors can affect earthworm population

densities, biomass and the species complex. Undoubtedly, the

obvious and most frequently cited are soil moisture, temperature

and reaction, each of which potentially can act as a complete

limiting factor. Other factors, such as soil depth and texture,

nutrient and food supply (vegetation species), physiographic

features (physiographic position, slope, aspect, elevation) and soil

colour can interact with the above factors and influence 'soil

conditions. ~ ,..~.

Soil Moisture

Given adequate and suitable food supplies, the presence

of available water in their immediate environment is the most

essential requirement for earthworms. Although the success

of any animal in a terrestrial environment depends largely

upon its ability to conserve water, mechanisms for such are

virtually absent in earthworms because respiration takes place

by diffusion of water-dissolved gases through the body wall.

This wall is therefore heavily vascularized and has a thin

cuticle. Water is also lost through the nephridia and dorsal

pores with excretory products and must be replaced.

Moisture studies relative to earthworms have been con-

cerned with percentag-e moisture content in the soil (Olson,

1928; Evans

&

Guild, 1947). Evans and Guild developed

regression coefficients based on activity, temperature and per

cent soil moisture. For several years, the senior author has

not been satisfied with this approach and has suggested an

alternative -

soil moisture tension

(Reynolds, 1973a). Since earth-

worms are 80-90% water by live weight (wet weight or fresh

weight biomass) (Grant, 1955a) and are able to withstand

desiccation of 70% or more of this water without ill effects

(Roots, 1956), the consideration should be shifted from per

cent soil moisture to soil moisture tension. This suggested

approach is reinforced by the fact that varying the soil texture

while keeping the per cent soil moisture constant will show the

soil moisture tension varies with the soil texture. Since earth-

worms must compete with plants and other organisms for the

water absorbed on the soil particles, the forces which the earth-

worms must exert to obtain this water (vs-plant-water adhesive

forces and soil-water adhesive forces) is more important than

the absolute amount of water present.

For example, consider two sites where the soil moisture

is 30 per cent at each. The moisture appears to be the same

at both sites under the current system. Suppose the soil

texture at one site is a sand, loamy sand or gravelly sand and

the other is a clay soil. The difference in the soil moisture

tension could be on the magnitude of 45X,

i.e.

the sandy soil

could be at

field capacity

or 1/3 Atm. (= .bar tension) and the

clay soil could be at

wilting point

or 15 Atm. One of the

chief advantages of the

tension method

is that it removes the

soil textural effect and places the emphasis on available

moisture. In the case of plants, water at 15 Atm. is unavail-

able regardless of the per cent moisture. The level at which

moisture is available for earthworms, or whether there are

species differences, is not presently known.

The sampling period (August 1971) was considered to be

a very dry season. In July 1971 precipitation occurred pre-

dominantly during the first half of the month, while the

August 1971 precipitation occurred after the sampling ended

on August 21. Because of limited field laboratory equiprrient,

measured soil moisture data were not obtained. Therefore, it

was necessary to rely on subjective tactile determinations.

These findings were then coded. Generally the upland soils

were drier unless the collection site was near a water source

such as a stream bank or the shore of a lake or pond.

Precise soil moisture data determinations would have been more

desirable.

Table 2. Correlation Matrix for Haliburton Earthworm Analysis.

Species

Juveniles

Aclitellate

Adults

Clitellate

Adults

Postclitellate

Adults

Total

Slope

Aspect

Elevation

'"

<lJ

'0

<lJ '"

0. <lJ

Vl

==

1.000

-0.197

-0.277

0.068

-0.318 0.486

-0.182 0.881

-0.010 0.004

0.025 -0.012

-0.089 0.080

c

<lJ

>

::l

<lJ

-",

"'-

=~

~1J

'e«

«

1.000

~

'"

~~

~.g

(3«

c,

1.000

<lJ",

~.:::

-::l

Qj1J

.-=:

«

o

1.000

0.542

0.358 0.327

0.445 0.134 1.000

Cii

(5

I-

1.000

<lJ

o

Vi

ti

<lJ

.{

u

:.c

a.'"

~ 0

0.0'';:;

o'(ij

'Vi 0

>-a..

it

0.725 0.695 0.525

0.061 -0.080 0.153 >-.001 1.000

c

o

.~

>

<lJ

m

0.030 -0.007 -0.024 -0.002 0.272 1.000

0.029 -0.075 -0.116 0.013 -0.056 0.089 1.000

pH

Physiographic -0.096 0.123 0.025

-O.OGO

-0.0460.047 -0.048 0.121

Position

1.000

0.752 1.000

I

0.049 -0.016 -0.052 0.035 0.011 -0.008 -0.096 -0.017 -0.275 -0.050

Moisture

Temperature -0.076 0.052 0.149 -0.034 0.116 0.063 -0.035 0.050 -0.176 -0.309

Hue

Value

Chroma

Sand

Silt

Clay

0.104

0.027 0.123 0.060 0.054 -0.095 0.099 0.379 0.125 0.119 0.103 -0.073 -0.261

-0.070 0.080 0.061 -0.140 0.077 0.011 0.144 0.075 0.011 -0.036 -0.014 0.038

0.085 -0.193 -0.123 0.023 -0.0.45 -0.134 -0.103 -0.036 -0.033 -0.149 -0.020 -0.037

-0.050 -0.066 0.020 -0.184 <0.001 -0.107 0.104 0.094 0.151 0.225 0.090 0.079

~

::l

'iii

Qj

E

<lJ

I-

~

.;

o

:2

<lJ

::l

I

1.000

<lJ

::l

~

1.000

'"

E

o

..c

u

1.000

1J

c

'"

<J)

1.000

1. 000

-0.038

-0.140 -0.003

0.005 -0.094 0.260

0.016 -0.235 -0.174 -0.187 -0.117 -0.261 0.144 0.107 0.009 -0.082 0.048 0.253 -0.069 0.014 0.287 0.292 1.000

10

o

1.000

Gravel

Organic Matter-0.12l

-O.OlD

-0.059 0.116 -0.080 0.018 0.058 -0.069 -Q.084 0.011 -0.021 -0.204 0.126 -0.133 -0.356 -0.345 -0.291 -0.228 -0.128 1.000

Vegetation

Vi

0.032 0.291 0.293 0.177 0.237 0.328 -0.128 -0.036 -0.014 0.046 -0.141 -0.078 0.006 0.067 -0.101 -0.185 -0.704 1.000

0.482

0.061 0.093 0.008 0.046 0.054 0.077 -0.080 -0.090 '.105 -0.018 0.056 -0.130 -0.063 0.093 -0.124 -0.233 -0.659

-0.001 -0.052 -0.050 -0.086 -0.107 -0.085 -0.130 -0.019 0.216 0.104 0.103 -0.020 0.058 -0.072 0.115 0.356 0.026 -0.359 -0.251 -0.098

0.017 -0.061 -0.115 -0.083 -0.003 -0.097 0.008 -0.133 0.213 0.169 0.075 -0.257 0.090 0.021 -0.030 -0.084 0.102 -0.122 -0.095 0.032

~

~

:2

.~

c

'"

ClIJ

o

0.007

~

o

1.000

'"

.12

'iii

t

<lJ

>

1.000

s:::

.t"'j

~

o

~

.....

5

o

.....

o

;...

w

4

A Preliminary Conceptual Model of Megadrile Activity

SoilTemperature

Michon (1954) when studying the effects of temperature

on the growth period in earthworms, reported that diapause

ends spontaneously, and in some species does not occur if

reared at low temperatures (9°C), even with adequate energy

sources and soil moisture availability. Studies by Doekson

and Wingerden (1964) did not confirm Michon's latter finding.

Kollmannsperger (1955) determined that the optimum tempera-

ture for surface activity of

Lumbricus terrestris

was 10.5°C pro-

viding there had been rain during previous days, indicating

that regardless of temperature, earthworms will migrate within

the soil profile if drying air is present. Grant (1955b) found

the upper lethal temperature for earthworms to be 25-27°C

but this could be increased by acclimatization. In the Smoky

Mountains (Reynolds, 1972c), the earthworms greatest activity

during the year occurred when the soil temperature was around

200C. The optimum soil temperature for the development

of six lumbricid species reported in this study is:

Allolobophora

turgia

12°C,

Dendrobaena rubida

18-20

o

C,

Eisenia foetida

25°C,

Eisenia

rosea

12°C,

Lumbricus rubellus

15-18°C and

Octolasion

cyaneum

15°C (Reynolds, 1973

after

Voisin, 1961). It should be

pointed out that

D.

rubida

and

E. foetida

are not true soil

dwelling species (=geobionts or euedaphics) but geophiles or

hemiedaphics.

Dendrobaena rubida

utilizes an under bark habitat

and

Eisenia foetida

is commonly referred to as the "manure-

worm". Therefore, it is not surprising to find that their optimum

developmental temperature is higher than that of the geobionts.

The soil temperature range of the sites in this study was

14-22°C(mean 16.8°C) which is close to the optimum tempera-

ture for development of many of the species encountered.

Soil Reaction

Wherry (1924) stated, "the life of the earthworm is very

strongly influenced by the reaction of the soil, so that they

can live only in slightly acid and neut.ral' soils ... earthworms

cannot live in raw humus which has a pH lower than

6 [H20]." Four years later, Olson reported the soil reaction

range for earthworms from Ohio to be pH 5.45-8.6 (H20)

saying that he believed that these organisms could not live in

soils beyond this range. A range of pH 6.3-8.1 (H20) was

reported for various habitats from several workers by Evans

and Guild (1947). From New Zealand, Lee (1959) wrote,

"since most soils are in the slightly acid to neutral range,

soil dwelling earthworms are not usually subjected to very high

or very low pH. Therefore, pH conditions have little in-

fluence on earthworms." This may be the case in New

Zealand, but Satchell (1967) reported on some European field

experiments with acid plots where the pH was 4.0-4.9 (H20).

Lumbricus

rubellus

tunnelled into the soil and lived, while

Allolobophora longa

remained on the surface and soon died.

Recently, Reynolds (1971 and 1972c) reported on studies in

the Smoky Mountains of east Tennessee where at lower

elevations (below 610 m) the pH was 5.3 (KC1) and at higher

elevations (610-915 m) dropped to pH 3.4 (KC 1). During

the same sampling period at even higher elevations (above

1525 m), earthworms were obtained in Inceptisols where the

pH was between 2.8 and 3.3 (KC1). No data exist for earth-

worms from soils at the upper end of the pH scale,

i.e.

pH values> 9.

The range of soil acidity of the sites in this study was

pH 3.9-7.2 (KCl) which is within the usual range reported

by most researchers.

SoilTexture

Guild (1948) investigated five broad soil textural groups

and .found significant differences in earthworm population

densities and species compositions. Several species were found

at too Iowa density to be tested statistically.

Allolobaphora

turgida (

=

Allolobophora caliginosa)

was the dominant species at

each of his sites and the population ratio showed the following

significant differences: light loam > medium loam = clay =

alluvium> gravelly sand.

In the original study (Reynolds, 1972a), the soil textural

groups were mainly in the coarser textures, ego sandy and

gravelly loams (Alfic Eutrochrepts). There were some black

mucks or organic soils (Histosols) in the river bottomlands.

In lieu of the time consuming and costly mechanical analysis

(pipette or hydrometer methods), tactile textural analysis was

performed by two soil scientists (Drs.

J.

R.

J

ared and R.

J.

Miller) skilled in this method.

Vegetation

Earthworms feed on dead and decaying plant remains,

or occasionally on animal remains. Because of their limited

capacity for moving about, they live very dose to their sources

of food.

Studies in leaf litter breakdown have been conducted by

Edwards and Heath (1963) and Heath

et al.

(1966). They

found the disappearance rates of leaf discs in fine mesh bags

in woodland soil to be: elm

(Ulmus)

> ash

(Fraxinus)

= lime

(Tilia)

> oak

(Quercus)

= beech

(Fagus).

When coarse mesh

bags were used to allow earthworms to act on leaf discs,

the same order of disappearance was observed. Sometimes the

rates of

Quercus

and

Fagus

disappearance were similar but

Quercus

always disappeared before

Fagus.

Their studies did not

include maple

(Acer).

The action of earthworms

(Lumbricus

terrestris)

on the disappearance of

Ulmus

and

Acer

was studied

by Reynolds and McBrayer (1968, unpub.). They found that

after the first few weeks the disappearance rates of these two

leaf species were almost identical, and thus corroborated the

observations of earlier workers that leaf disappearance and

palatability for earthworms are positively correlated.

i.e.

the

quickly disappearing species

(Ulmus

and

Acer)

are more palat-

able than the slowly decomposing species

(Quercus

and par-

ticularly

Fagus).

These factors were also reflected in a study

of earthworm density and biomass in six heterogeneous wood-

lot sites by Reynolds (1972b). Additional reports by Witkamp

and Olson, (1963) and Reynolds (1972a) give an expanded leaf

palatability scale:

Robinia

> >

Alnus

=

Populus

>

Prunus

=

Salix

=

Ulmus

=

Acer

=

Liriodendron

>

Fraxinus

=

Tilia

=

Gleditsia

=

Betula> Quercus

=

Fagus.

None of the previous

studies utilized any conifers. A number of conifers were

encountered in this study:

Abies

(fir),

Larix

(tamarack),

Picea

(spruce),

Pinus

(pine),

Thuja

(cedar) and

Tsuga

(hemlock).

Species of these genera would be at the lower end of the

scale,

i.e.,

<Fagus.

Elevation

Reynolds (1971 and 1972c) correlated changes in species

composition with changes in elevation. At elevations below 610

m in the Smoky Mountains, the megadrile faunal composition

was

Octolasion-Pheretima-Diplocardia-Bimastos

while at higher ele-

vations (above 610 m) the faunal composition was

Octolasum-

Pheretima-Allolobophora-Dendrobaena.

It might be coincidental that

as one increases in altitude in the Smoky Mountains, the habi-

tats become similar to those found as one moves northward

latitudinally, and the earthworm faunal composition becomes

similar to populations in more northerly regions. For example,

Dendrobaena

replaces

Bimastos

and

Allolobophora

replaces

Diplocardia

as previously described in the Post Quaternary

Introduction theory for megadrile introduction and establish-

ment in North America (Reynolds

et al.,

1974; Reynolds,

1973b, 197&, 1973d and 1974).

The range in elevations of the sites in this study was

685-1122 m which is too narrow and too low to show

significant differences relating to earthworm distribution.

MEGADRILOGICA

5

Physiographic Position

A discussion of preliminary observations of megadrile

distribution in the physiographic regions of the eastern United

States,

i.e.

faunal changes in moving from the Coastal Plain

to the Allegheny Mountains, was presented by Reynolds (1974).

There were in this study only three physiographic posi-

tions - bottomland, terrace and upland. Physiographic position

is closely related to elevation. In areas of greater megadrile

diversity, certain species will occupy specific habitats of various

physiographic positions. For example, on the flood plains of

the bottomland areas, earthworm species such as

Allolobophora

chlorotica, Eiseniella tetraedra

and

Spargonophilus eiseni

will be more

abundant than on any other level.

Slope, Aspect and Soil Colour

The three remaining variables (factors), as far as we know,

have not been examined previously. All three are related to

soil temperature and that is why they were examined. Slope

and aspect are related to the angle of incoming solar radiation

while soil colour is important in the absorption of that radia-

tion.

The Munsell Colour Notation

(eg.

lOYR 3/4) is composed

of three parts: hue (lOYR), value

(31)

and chroma (/4). Hue

is the dominant spectral colour. In this study nearly all hues

were 10YR. Value (brilliance) refers to the relative lightness

of colour

i.e.

when the value increases from 2 to 8, the

colours become lighter. In this study the values ranged from

2 to 6 with a mean of 4.3. Chroma (saturation) is the relative

purity of strength of the spectral colour and increases with

decreasing grayness,

i.e.

as chroma decreases from 8 to 0,

the colour becomes grayer. In this study the chromas ranged

from 0 to 6 with a mean of 3. Both values and chromas

averaged at about the centre of each scale.

Interactions

The many ecological factors affecting earthworm popu-

lations produce a complex system which can be diagramatically

represented (Figure 1).

The major habitat factors (rectangles) affecting earthworms

activity are: soil moisture, soil temperature, soil reaction and

vegetation.

Soil moisture is the factor which controls earthworm

aestivation (inactivity) during the warm portions of the year.

Soil moisture interacts with the other major factors: soil

temperature

(a) -

by increasing the conductivity in the soil

of incoming radiation; vegetation

(b) -

soil moisture has an

effect with other factors on the suitability of a habitat for

certain tree species and soil acidity

(c) -

variations in soil

reaction are produced, in part, by variations in the amount

of moisture in the soil, hence the use of KC1 pH determina-

tions to remove the influence of soil moisture.

Soil temperature is the factor which controls earthworm

hibernation (inactivity) during the cold portions of the year.

The interaction involves thermal conductivity in the soil. Soil

temperature also governs the developmental rate of earthworms

and their cocoons.

Vegetation is influenced by soil temperature and soil

moisture plus many additional factors. The importance of

vegetation regarding available nutritional requirements for earth-

worms was discussed earlier. The presence of conifers on the

site usually increases the acidity of the litter and then the

soil

(d).

The type of vegetation influences the type and amount

of litter, its decomposition and hence, its availability as a

buffer against solar radiation and water runoff.

Soil reaction is a more complex situation. It may not be

the reaction itself which affects earthworm activity but other

soil interactions which are governed by the level of soil reaction.

An example of such interaction involves mineral bonding. At

low pH values (high acidity), elements such as aluminum, cal-

cium and iron are bound in an unavailable state or in a non-

exchangeable condition. Determination of exchangeable calcium

has been shown to affect earthworm populations (Satchell,

1955). Therefore, it is highly probable that other mineral

bonding affected by soil reaction and as yet unknown might

affect earthworm activity.

The next group of habitat factors (circles) may affect

earthworm activity directly, or as in most cases, may influence

or regulate one or more of the major (primary) factors.

These secondary factors are: soil texture, soil colour, slope,

aspect, physiographic position, elevation, soil minerals, and

climate.

Soil texture influences soil moisture

(e),

soil temperature

Ij),

vegetation (g) and soil acidity

(h').

The size of soil separ-

ates (smaller separates have a greater surface area) affect the

tension of the soil moisture on these separates,

i.e.

greater

surface area

=

greater moisture tension

=

available moisture

for earthworms and plants (vegetation)

(=

pathway

e - b).

The direct soil textural effect on vegetation (g) involves a suit-

able substrate for the vegetation. The soil reaction - textural

pathway

(h)

begins with the tertiary (hexagon) factor (parent

material), its breakdown and bonding (exchangeable ions) even-

tually influencing the soil reaction. Another tertiary factor

affecting texture is structure

(i)

(Buckman

&

Bradv, 1969,

p. 60-3). The gravitational forces producing colluvial soils are a

result of the slope influences on texture

(j).

Soil colour influences soil temperature

(h)

where the darker

soils,

ego

dark hues, low values and high chromas absorb and

conduct more of the incoming solar radiation. The tertiary

factor, parent material, influences the colour of soil (I), as

does the amount of organic matter

(m)

coming from the vege-

tation. Therefore, one of the

(b)

pathways between vegetation

and soil moisture passes through soil colour, as the greater

the organic matter content of the soil, the greater its water-

holding capacity.

Slope influence on soil texture

(j)

has been mentioned.

Slope and aspect affect soil temperature

(n, n', n").

The greater

the degree of slope in these latitudes, the more directly the

sun's rays strike the earth's surface causing greater absorption

of the solar radiation (heat). Equally important is the aspect.

The optimum degree of slope facing in the wrong direction

will have the opposite effect on soil temperature. The effect

of slope on soil moisture

(0),

involves the rapid removal of

gravitational water from the soil. The slope effect on vegeta-

tion

(P)

involves a slope-texture-soil moisture relationship. The

aspect-vegetation interaction

(q)

involves a soil temperature

relationship on vegetation

(b).

Physiographic position and elevation are interrelated

(r), ego

bottomlands are always lower than terraces and uplands in a

given area. Like the slope-soil moisture pathway

(0),

these

factors affect soil moisture (s.s') mainly through gravitational

action on moisture at low tension. The pathways to vegetation

(t,t') revolve around low wet positions favouring certain tree

species and earthworm species while changes at higher eleva-

tions via soil moisture and soil temperature interact on soil

acidity and vegetation. Where great elevational differences

occur, there may be an elevation-soil temperature effect

(u).

There is a 2°C drop in air temperatures for each

increase of 300 m in elevation (Schroeder and Buck, 1970).

This lower air temperature will cause a decrease in the soil

temperature. Although soil temperatures are slow to change

and change very little compared to air temperatures, there is

a gaseous exchange between the atmospheres above and below

the soil surface, thus creating a lowering of the soil temperature.

Soil elements were not studied here, but their presence

in the soil is important to earthworms in two ways: 1) as

essential elements for physiological biochemical reactions, and 2)

as metal concentrations in the earthworms' tissues which may

later prove to be lethal. Studies of metal residues in earth-

worms have not been reported until recently (Gish and Chris-

tensen, 1973). The availability of these elements to enter into

reversible reactions is often a function of soil acidity

(v);

in

most cases, a decrease in acidity

=

a decrease in availability.

Since earthworms are omnivorous and rarely carnivorous (more

accurately saprophagous), their source of protein (nitrogen in

particular) is derived from that found in litter or the soil which

they ingest. Nitrogen is highly mobile and leaches quickly,

therefore, it.savailabilityis going to be influenced by vegetation,

soil moisture and soil texture.

As mentioned earlier, earthworm respiration takes place

through the moist body wall. The soil atmosphere is influ-

enced by soil texture

(w)

and soil structure

(w')

which governs

the size and number of pore spaces in the soil. The avail-

ability of soil atmosphere can be reduced by an increase in

gravitational soil water usually from precipitation

(x)

which even-

tually influences the soil moisture via pathways,

x-i-e

or

x-ta-tu-e.

Earthworm respiration is affected by the following: activity,

diurnal rhythm, oxygen tension, carbon dioxide concentration,

exposure to light, ambient temperature and earthworm bio-

volume.

Three last factors to be mentioned which were not studied

but which do affect earthworm activity are cloud cover (light

intensity), relative humidity and wind. Earthworms are

extremely sensitive to ultra-violet radiation (Reynolds, 1973a)

and the longer wavelength heating rays which create a lethal

water imbalance. The amount of ultra-violet and the per cent

relative humidity decrease with an increase in cloud cover

(Robertson, 1967; C. Young, pers. comm.). Earthworms are

generally found living below the

0

soil horizons. The senior

author has observed unpigmented earthworm species

(Allolo-

bophora turgida

and others) crawling on the surface of the soil

during cloudy days when the relative humidity was high

(R.H. 80+ %). It has been reported that the highly pigmented

earthworm species are more resistant to the damaging effects

of the short wavelengths,

ego

ultraviolet light (Stephenson, 1930).

Thus, it was most unexpected to note unpigmented and low

pigmented species on. the surface. One species

(Lumbricus ter-

restris)

which normally and regularly feeds on the surface, does

so usually at night when light is not a factor. Generally, this

nocturnal activity is during the period of the day when the

relative humidity is the greatest. Cloud cover will also reduce

the heating wavelengths reaching the soil and thus soil tempera-

ture

(y),

through soil colour

(y-k

pathway). Research has shown

that up to 40% of the heat lost by surface soil .radiation on

clear nights

(eg.

no cloud cover) is carried off by convection

streams (Molga, 1962, p. 85). This would be shown by pathway

y'

going directly from cloud cover to soil temperature.

Wind is important as a drying agent both for the soil

(z),

(z'-z"-i-e)

or

(z-a)

pathway and the earthworm. If these

animals, without moisture retention mechanisms are continu-

ously exposed to drier (low R.H.) moving air (wind)

(z')

the

rcsulta would be fatal. Many people have seen dead earth-

worms on driveways and sidewalksafter a rain. The immediate

assumption of drowning is probably incorrect, because earth-

worms can withstand long periods of submersion (Guild, 1951;

Roots, 1956; Reynolds

et al.,

1974), and the more plausible

explanation is exposure to lethal ultra-violet and/or drying air

as the earthworms cannot return to the soil easily through the

impervious concrete. Similar situations occur in the tropics

(Gates, pers. comm.). In Burma, on clay soils after a rain

the burrows or exit holes are filled with soil particles and the

earthworms are trapped on the surface, unable to penetrate

the drying clay and reenter their protective environment.

Relative humidity also through gaseous exchange interacts with

the soil atmosphere

(z").

These are by no means all the factors and interactions

involved in earthworm activity. The challenge was presented

to model habitat data and earthworm activity. This paper

should be considered as a preliminary conceptual model in the

search for the factors and their interactions on megadrile

activityand distribution.

In retrospect, four limitations in this study were: 1) coded

vs

measured data, 2) sampling in a region of low earthworm

density, 3) sampling during a dry period of the year (Reynolds,

1972a), and 4) sampling in too small a geographical area,

i.e.

limited range within each variable analyzed. This fourth

point is assumed because despite the low factor correlation

(Table 2), these factors are important in megadrile activity and

distribution.

In summary, we can suggest that megadrile activity IS

represented by the following equation:

Earthworm Activity

=

j[pH, st,sm,v,t,c,s,a,pp,e,pm,sa,ss,se ... ]

where: pH

=

soil reaction, st

=

soil temperature, srn

=

soil

moisture, v

=

vegetation, t

=

soil texture, c

=

soil colour,

a

=

aspect, s

=

slope, pp

=

physiographic position, e

=

elevation, pm

=

parent material, cl

=

climate (precipitation,

wind, relative humidity, cloud cover), sa

=

soil atmosphere,

ss

=

soil structure, se

=

soil minerals (elements), and ...

are other factors not yet determined.

ACKNOWLEDGEMENTS

The authors wish to express their appreciation to D. L.

Dindal, College of Environmental Science and Forestry (Syra-

cuse, NY), A. T. Easley and A.

J.

Kayll, Faculty of Forestry

(UNB), R. D. Mercer, Department of Forestry and Agriculture

(St. John'S, Nfld.) and W. M. Reynolds, Tall Timbers Research

Station (Tallahassee, FL) for reviewing the manuscript, their

comments, criticisms and suggestions. The authors wish to

express their gratitude to Ms. S. Ross, Faculty of Forestry

(UNB) for producing the final figure in this text and to Ms.

F. Forrester, FacuItyof Forestry (UNB) for computer and typing

assistance.