Biodiversity Survey Discussion Examples | Species Richness, Dominance, Diversity Indices, and Sources of Error

Plants and insects were surveyed at Site A, a deciduous forest; Site B, a park grassland; and Site C, a pond margin, using the same survey area and duration.

Plant species richness was 12 at Site A, 9 at Site B, and 15 at Site C. Total plant abundance was 64 at Site A, 104 at Site B, and 87 at Site C.

The plant Shannon index was 2.21 at Site A, 1.84 at Site B, and 2.48 at Site C. Simpson diversity was 0.86 at Site A, 0.78 at Site B, and 0.90 at Site C.

At Site B, white clover was most abundant at 26 individuals, with a relative dominance of 25.0%. The proportion of invasive plants was 21.2%, the highest of the three sites.

The numbers of insect taxonomic groups detected were 14 at Site A, 12 at Site B, and 17 at Site C, with Site C having the highest value.

Sites A and B shared four plant species, giving a Jaccard similarity of approximately 0.24.

Overall, Site C had high plant and insect richness and diversity indices, whereas Site B had high total abundance but also high proportions of particular dominant species and invasive plants.

This survey compared species richness, abundance, dominance, and diversity indices of plants and insects among three contrasting environments: deciduous forest, park grassland, and a pond margin.

Plant species richness was highest at Site C, with 15 species, and its Shannon index, Simpson diversity, and evenness were 2.48, 0.90, and 0.92, respectively.

Site C included a pond, waterside wetland, and adjoining grassland, so both species favoring dry conditions and those favoring moist conditions could potentially occur there.

Such transition zones where different environments meet can provide a variety of habitat conditions and therefore support multiple biological groups.

Site C also had the highest number of insect taxonomic groups, 17, and dragonflies were especially abundant, with 17 individuals.

The pond provides aquatic habitat for dragonfly larvae, while surrounding grassland and vegetation provide places for adults to rest, forage, and emerge.

The continuity of aquatic and terrestrial habitats may therefore have increased insect diversity.

Site A had fewer plant species than Site C, at 12, but its Shannon index of 2.21 and evenness of 0.89 were relatively high.

Forest-adapted species such as Konara oak, Japanese blue oak, and ferns were found at Site A. Because the canopy limits sunlight, grassland plants requiring strong light were likely less common.

On the other hand, diverse microhabitats occur vertically and structurally in litter, bark, fallen wood, and soil, which may explain the relatively high number of beetles.

Site B had the highest total plant abundance, 104 individuals, but the lowest species richness, 9, and the lowest Shannon index, 1.84.

This shows that high abundance does not necessarily mean high biodiversity.

At Site B, a few species such as white clover, plantain, Japanese silver grass, and invasive plants accounted for much of the community.

Park grasslands are repeatedly disturbed by mowing, trampling, and cleaning. Species tolerant of such disturbance may become dominant, while species dependent on forests or wetlands may decline.

The proportion of invasive plants at Site B was 21.2%, higher than the 4.7% at Site A and 9.2% at Site C.

In places with frequent movement of people and vehicles, construction, and lawn management, seeds can be introduced easily and invasive plants adapted to disturbed habitats may establish readily.

However, the mere presence of invasive species does not by itself mean that the environmental condition of a site is poor.

Their effects should be assessed through continued surveys of competition with native species, occupation of plant communities, and impacts on ecosystem functions.

The Jaccard similarity between Sites A and B was approximately 0.24, indicating relatively few shared plant species.

This likely reflects major differences in light, moisture, management, and human disturbance between the shaded forest at Site A and the sunny grassland at Site B.

Sites A and C shared seven species and were more similar than Sites A and B.

This may be because parts of Site C contained trees and shade, allowing some species associated with forest edges to occur there.

However, similarity indices based only on presence or absence do not reflect differences in abundance. The same species may occur as one individual at one site and as many individuals at another.

For more detailed comparisons of community structure, abundance-based measures such as Bray–Curtis dissimilarity can also be used.

In the seasonal survey, total species richness was highest in summer at 60 species. Insects were especially diverse, with 31 species, likely because higher air and water temperatures, plant growth, flowering, and increased food resources promoted activity.

In winter, insect richness fell to five species, whereas bird richness was highest at 14 species.

This may reflect the arrival of wintering birds and the greater visibility of birds in trees after leaves have fallen.

Therefore, a survey conducted in only one season cannot fully characterize the biodiversity of an area.

Among the diversity indices, Site C had the highest values and Site B the lowest. However, a site with a high diversity index is not necessarily the most important for conservation.

Even a site with low species richness may have high conservation value if it supports rare species or species dependent on a particular habitat.

In addition, invasive species can sometimes increase apparent species richness, so native, invasive, rare, and indicator species should be examined separately.

Although survey area, duration, and number of observers were standardized in this study, detection probability varies with weather, time of day, and observer experience.

Insects are strongly affected by temperature and wind, bird detections depend on the ability to identify calls, and plants may be difficult to identify when flowers or fruits are absent.

It is therefore important to survey the same sites repeatedly and integrate results from different seasons and times of day.

Unidentified organisms should not simply be excluded, because doing so underestimates diversity. Recording them separately as “Unknown Species A” or “Beetle A” allows later identification from photographs and field guides.

Overall, the complexity created where aquatic and terrestrial habitats meet likely contributed to the high plant and insect diversity at Site C.

Site A supported a forest-specific biota, while at Site B a small number of species tolerant of human management and disturbance were dominant.

Biodiversity should therefore be evaluated not only by species richness but also by evenness of abundance, species composition, invasive and rare species, habitat conditions, and seasonal change.

If species richness is high but the diversity index is low, abundance may be concentrated in one or a few species. Relative dominance and evenness should be examined in addition to species richness.

If total abundance is high but species richness is low, a few species adapted to the environment may dominate. Disturbances such as mowing, trampling, drying, or eutrophication may contribute to simplification of the community.

A high abundance of invasive species may result from seed introduction by people or vehicles, construction, bare-ground formation, or frequent management. Their abundance and distribution should be monitored over time to evaluate effects on native species.

Few shared species may indicate that environmental conditions such as light, moisture, vegetation structure, land use, and management differ, resulting in different biological communities at each site.

Differences among survey rounds may result from season, weather, time of day, organism movement, and observer detection rates. Rather than drawing conclusions from a single survey, use averages and frequencies from repeated surveys.

If a rare species is detected, the site may retain food resources, breeding sites, vegetation, moisture conditions, or other habitat features used by that species. Exact location information should be handled carefully, and repeated surveys should be used to assess persistence and habitat conditions.