Invertebrate Biodiversity in Woodland on the University of Lincoln Riseholme Campus

Results of an analysis carried out by Level 3 students in 2006 compiled by Charles Deeming

This study investigated the diversity of invertebrates found in three different types of woodland on Riseholme Campus:

The hypothesis of the study was that the different habitat types would influence the biodiversity of the invertebrates living on the ground. As well as direct comparison of the species variability at the three sites, two types of diversity indices were calculated to get a comparative measure of the invertebrate biodiversity of the three habitats.

 

Figure 1. A) Setting a pitfall trap; B) A trap in situ.

In early October 2006 students laid pitfall traps in a random layout in the three habitats (Figure 1). Each traps consisted of a plastic cup sunk into the ground, filled with ~20 ml of diluted anti-freeze and covered by a Petri-dish lid. The contents of the traps were collected after 7 days. The students sorted and identified the invertebrate species to Order level using a standard identification key (Tilling, 1987). Numbers of each taxonomic group in each pitfall trap were recorded. Using this data Shannon and Simpson diversity indices were calculated per sample. Species and indices data were analysed using one-way analysis of variance (ANOVA).

The total numbers of individual invertebrates were significantly affected by the type of woodland (Table 1). The average number of animals per pitfall trap was highest for the Sycamore plantation and lowest for the Coniferous woodland.

The mean numbers of invertebrate taxa collected per trap were also significantly influenced by the woodland type (Table 1). Whilst the average number of taxa per pitfall trap was highest for the Sycamore plantation, the lowest values were observed for the Mixed woodland. A total of 14 different taxa were recorded from the Mixed woodland, 16 taxa from the Sycamore wood and 15 taxa from the Coniferous habitat.

Table 1. Mean values (± SD) for mean total number of invertebrates, and the mean number of taxa caught, in pitfall traps set in the three woodland types. Results of one-way analysis of variance are as indicated.
	Mixed Deciduous Woodland (N = 27)	Sycamore Plantation (N = 30)	Coniferous Plantation (N = 30)	One-way ANOVA
Mean total number of invertebrates per trap	72.2 ± 33.6	111.5 ± 69.1	31.3 ± 24.6	F2,84 = 21.86, P < 0.001
Mean number of taxa represented in each trap	5.8 ± 1.5	7.4 ± 2.4	6.4 ± 2.2	F2,84 = 3.69, P < 0.05

The distribution of invertebrate taxa caught in the three habitats are illustrated as pie-charts in Figure 2. In mixed woodland harvestmen (Opiliones) and beetles (Coleoptera) were over 75% of all animals caught in the traps. By contrast, these two groups were only just over 50% of the animals caught in the Sycamore plantation and less than 25% of the animals caught in the Coniferous woodland. Springtails (Collembola) were common in the Sycamore plantation (Figure 2). No particular taxa dominated the species found in the coniferous woodland (Figure 2).

Figure 2. Pie-charts showing the distribution of different invertebrate taxa collected in the three different woodland habitats. Values are derived from mean values for numbers of individual animals caught in traps.

The mean numbers of each taxa in the three habitats are shown in Figure 3. On average almost 50 harvestmen and 15 beetles were caught per trap in the Mixed woodland. Sycamore woodland had comparable numbers of harvestmen but more beetles (over 20 per trap) and almost 20 springtails per trap (Figure 3). Coniferous woodland had a low invertebrate count for all taxa with the highest counts being for woodlice (Isopoda), spiders (Aranae) and mites (Acarina). In all habitats the beetles were mainly from the Family Carabidae.

  

 

 

 

 

 

 

 

 

 

 

 

Figure 3. Mean number of animals caught per pitfall for each taxon observed in the three different types of woodland. Significant effects of woodland tested by one-way analysis of variance are as indicated : * = P < 0.05; ** = P < 0.01; *** = P < 0.001. The absence of an asterix indicates that woodland type did not significantly affect the mean number of animals caught per taxon.

The Shannon and Simpson diversity indices were calculated for each sample from each woodland type. Average values are shown in Table 2. In each of these measures of biodiversity the lowest values, i.e. the poorest invertebrate diversity, were seen in the Mixed woodland and the highest was for the Coniferous woodland (Table 2). The Sycamore plantation had intermediate values. One-way analysis of variance showed that the type of woodland had a significant effect (Table 2) on invertebrate biodiversity on Riseholme Campus.

Table 2. Mean values (± SD) for Shannon and Simpson diversity indices for the three woodland types. Results of one-way analysis of variance are as indicated.
	Mixed Deciduous Woodland (N = 27)	Sycamore Plantation (N = 30)	Coniferous Plantation (N = 30)	One-way ANOVA
Shannon diversity index	0.960 ± 0.219	1.317 ± 0.375	1.448 ± 0.369	F2,84 = 16.16, P < 0.001
Simpson diversity index	2.059 ± 0.514	3.177 ± 1.119	4.641± 1.967	F2,84 = 25.92, P < 0.001

The three different habitats were represented by a variety of species, most of which were found in the three types of woodland but in quite different frequencies. The invertebrate diversity in the three woodland types was significantly different and this did not necessarily correspond with numbers of animals caught. Whilst the number of animals caught per trap in Mixed woodland were much higher than in coniferous woodland the diversity of species was very much lower in the former habitat; most of the increased capture rate was associated with only two species. In the coniferous woodland, whilst the total number of invertebrates caught per pot was low their diversity was high – no one taxon dominated the fauna. For the Sycamore plantation both numbers and diversity were the highest recorded in the study but three taxa dominated the fauna.

The reasons for this distribution of taxa may lie in the quality of the habitat to support different invertebrates. For instance, springtails were commonly found in the traps laid in the Sycamore plantation but were almost absent from the mixed woodland. The latter habitat had a good covering of low-growing plants which were absent in the Sycamore habitat; springtails were slightly more common in coniferous woodland which also had little ground vegetation. Whether this distribution of springtails represents adoption of a good habitat, or the absence of predators, in the Sycamore plantation is unclear and would merit further investigation.

Coniferous habitats may serve as a home to a greater diversity of species than other habitats but the numbers of any particular Order are low. Other habitats are able to support higher species numbers and this can affect diversity.

However, another possibility to explain this distribution may lie in the size of the habitats themselves. The pitfall traps were laid centrally in an area of mixed woodland that is ~100 m wide and perhaps 400 m long. By contrast, the Sycamore and the Coniferous plantations were smaller, only 50 m wide and 150 m long. In these two sites, it is possible that the pitfall traps caught some types of invertebrates that were only passing through the habitat rather than inhabiting the habitat on a long term basis.

Further investigation could set pitfall traps based on a specific grid pattern, which could be related to the position relative to the edge of the woodland. The species numbers and diversity could then be plotted on this grid to determine whether location is important in the type and number of invertebrates caught in the traps.