Results
Species richness at TF
A total of 22 species of butterflies were recorded in 82 butterfly counts (surveys with no species name recorded were excluded) at 42 TFs with a mean of 1.76 species per survey. The average number of species recorded per TF was 3.88, with a maximum of 9. The most widespread species were small white (24 TFs), large white (18 TFs), and common blue (8). The most abundant were small white, large white and small heath. Simpson diversity index (SDI) varies with species richness (SR) - TFs with higher SR and SDI have greater butterfly diversity.
Within each taxonomic group, SR and SDI were significantly correlated, but there was little association between groups apart from SDIs for ground dwellers (ants excluded) and pollinators ?@fig-ft-but-sr-1.
SPAC
For butterfly species, 22 butterfly species (gamma diversity) were observed in 51 surveys across 41 TFs. As SACs show (Figure 2), saturation is nearly achieved implying that the vast majority of butterfly species occupying these areas have were spotted in the surveys. For ground-dwellers and pollinators, saturation was reached at 13 and 10 species groups respectively, and for both is achieved within a relatively small number of surveys. [discussion - relatively difficulty of observing butterflies, relatively less ‘effort’ per survey - may need fewer pollinator and ground-dweller surveys to estimate gamma diversity].
##3 Survey level analysis
Model outcomes
# A tibble: 7 × 7
effect group term estimate std.error statistic p.value
<chr> <chr> <chr> <dbl> <dbl> <dbl> <dbl>
1 fixed <NA> (Intercept) 1.79 0.0387 46.2 0
2 fixed <NA> month 0.00948 0.0314 0.302 0.763
3 fixed <NA> mean_age_days 0.0316 0.0599 0.528 0.597
4 fixed <NA> y 0.0759 0.0353 2.15 0.0318
5 fixed <NA> mean_ht 0.133 0.0683 1.95 0.0509
6 fixed <NA> shannon -0.112 0.0424 -2.65 0.00807
7 ran_pars tiny_forest_id sd__(Intercept) 0.179 NA NA NA
X.Intercept. | mean_age_days | mean_ht | month | shannon | y | AICc |
---|---|---|---|---|---|---|
1.8 | 0.16 | -0.118 | 0.077 | 863 | ||
1.8 | 0.031 | 0.14 | -0.113 | 0.076 | 865 | |
1.8 | 0.16 | 0.0085 | -0.118 | 0.077 | 865 | |
1.8 | 0.15 | -0.113 | 866 | |||
1.8 | 0.121 | -0.069 | 0.066 | 867 | ||
1.8 | 0.032 | 0.13 | 0.0095 | -0.112 | 0.076 | 867 |
1.8 | 0.040 | 0.11 | -0.106 | 867 | ||
1.8 | 0.102 | 0.067 | 868 | |||
1.8 | 0.15 | 0.0080 | -0.113 | 868 | ||
1.8 | 0.116 | -0.069 | 868 |
# A tibble: 7 × 7
effect group term estimate std.error statistic p.value
<chr> <chr> <chr> <dbl> <dbl> <dbl> <dbl>
1 fixed <NA> (Intercept) 1.60 0.0462 34.7 1.64e-263
2 fixed <NA> month 0.0265 0.0445 0.595 5.52e- 1
3 fixed <NA> mean_age_days -0.0648 0.0674 -0.961 3.37e- 1
4 fixed <NA> y -0.0682 0.0454 -1.50 1.34e- 1
5 fixed <NA> mean_ht 0.169 0.0762 2.21 2.68e- 2
6 fixed <NA> shannon -0.0638 0.0509 -1.25 2.10e- 1
7 ran_pars tiny_forest_id sd__(Intercep… 0.0642 NA NA NA
X.Intercept. | mean_age_days | mean_ht | month | shannon | y | AICc |
---|---|---|---|---|---|---|
1.6 | 0.096 | -0.067 | 522 | |||
1.6 | 0.106 | 522 | ||||
1.6 | 0.136 | -0.061 | 523 | |||
1.6 | 0.124 | -0.059 | -0.066 | 523 | ||
1.6 | 0.086 | 0.036 | -0.071 | 524 | ||
1.6 | -0.048 | 0.142 | 524 | |||
1.6 | 0.099 | 0.028 | 524 | |||
1.6 | -0.042 | 0.128 | -0.066 | 524 | ||
1.6 | -0.072 | 0.196 | -0.074 | 524 | ||
1.6 | -0.065 | 0.179 | -0.071 | -0.065 | 524 |
# A tibble: 7 × 7
effect group term estimate std.error statistic p.value
<chr> <chr> <chr> <dbl> <dbl> <dbl> <dbl>
1 fixed <NA> (Intercept) 8.11e-1 0.0979 8.29 1.13e-16
2 fixed <NA> month 2.43e-2 0.102 0.238 8.12e- 1
3 fixed <NA> mean_age_days 1.65e-2 0.137 0.120 9.04e- 1
4 fixed <NA> y -6.94e-2 0.105 -0.664 5.07e- 1
5 fixed <NA> mean_ht -2.16e-1 0.150 -1.44 1.50e- 1
6 fixed <NA> shannon -4.11e-3 0.108 -0.0380 9.70e- 1
7 ran_pars tiny_forest_id sd__(Intercept) 5.01e-6 NA NA NA
X.Intercept. | mean_age_days | mean_ht | month | shannon | y | AICc |
---|---|---|---|---|---|---|
0.81 | -0.19 | 187 | ||||
0.82 | 188 | |||||
0.81 | -0.21 | -0.071 | 189 | |||
0.82 | -0.109 | 189 | ||||
0.81 | 0.028 | -0.21 | 189 | |||
0.81 | -0.19 | 0.0175 | 189 | |||
0.81 | -0.19 | -0.0099 | 189 | |||
0.82 | -0.0545 | 190 | ||||
0.82 | -0.025 | 190 | ||||
0.82 | 0.0043 | 190 |
Model outcomes
Descriptive analysis of SR by taxa at TFb
As Figure 12 shows insects, vasculat plants and birds are the most diverse taxa across all habitat type. Insect and plant diversity are greatest in residentail gardens; bird and mamal diversity are siialr betwen gardens, grasslant and arable land.
Summary of environmental predictors
Category | Metric | Mean | Sd | Q25 | Q75 |
---|---|---|---|---|---|
Blue_infrastructure | still_water | 21590 | 39716 | 2451 | 21590 |
Blue_infrastructure | watercourse | 39287 | 135997 | 3753 | 39287 |
Blue_infrastructure | nearest_water | 276 | 251 | 82 | 410 |
Built | built_area | 2086421 | 653916 | 1694140 | 2591003 |
Climate | tf_temp_2020 | 10.88 | 0.76 | 10.65 | 11.17 |
Climate | tf_temp_2022 | 11.27 | 0.70 | 11.02 | 11.56 |
Climate | tf_rain_2020 | 70 | 20 | 59 | 71 |
Climate | tf_rain_2021 | 61.5 | 13.1 | 54.6 | 63.1 |
Climate | tf_rain_2022 | 55.8 | 14.7 | 47.8 | 57.5 |
Climate | mean_spring_rain | 145 | 29 | 130 | 153 |
Climate | mean_spring_temp | 9.28 | 0.66 | 9.02 | 9.55 |
Connectivity | nc_y | 10.0 | 3.8 | 7.0 | 12.0 |
Connectivity | lnk_y | 136 | 95 | 58 | 205 |
Connectivity | slc_y | 113078 | 131052 | 26100 | 144700 |
Connectivity | msc_y | 21423 | 53115 | 5630 | 21423 |
Connectivity | ccp | 0.48 | 0.22 | 0.32 | 0.66 |
Connectivity | lcp | 0.0046 | 0.0110 | 0.0000 | 0.0046 |
Connectivity | cpl | 2.7 | 1.1 | 1.9 | 3.2 |
Connectivity | ecs | 94889 | 124745 | 17650 | 117182 |
Connectivity | awf | 6042740107 | 17522014830 | 173363627 | 3765155663 |
Connectivity | iic_y | 0.0026 | 0.0071 | 0.0000 | 0.0000 |
Green_infrastructure | perc_tree | 0.0187 | 0.0245 | 0.0038 | 0.0220 |
Green_infrastructure | perc_garden | 0.201 | 0.089 | 0.136 | 0.260 |
Green_infrastructure | perc_veg | 0.41 | 0.16 | 0.32 | 0.50 |
Green_infrastructure | wood_area_sum | 227252 | 202858 | 82726 | 327279 |
Green_infrastructure | gi_prop | 0.55 | 0.18 | 0.42 | 0.68 |
Green_infrastructure | tree_density_m_2 | 0.73 | 0.36 | 0.49 | 0.98 |
Greenness | green_prop | 0.30 | 0.21 | 0.12 | 0.44 |
Greenness | ndvi | 0.51 | 0.10 | 0.46 | 0.57 |
Greenness | savi | 0.263 | 0.071 | 0.218 | 0.306 |
Greenness | gbndvi | 0.28 | 0.12 | 0.23 | 0.35 |
Greenness | evi_2 | 0.310 | 0.086 | 0.256 | 0.361 |
Landscape | aggregation_index | 92.4 | 2.1 | 91.0 | 94.0 |
Landscape | modified_simpsons_diversity_index | 0.89 | 0.31 | 0.69 | 1.11 |
Landscape | perimeter_area_fractal_dimension | 1.317 | 0.027 | 1.303 | 1.335 |
Landscape | patch_richness | 8.3 | 1.6 | 7.0 | 9.0 |
Landscape | shape_index | 47.1 | 8.2 | 41.1 | 52.4 |
Linear_features | hedge_len | 3870 | 2898 | 1575 | 5692 |
Linear_features | road_length | 40002 | 11801 | 33248 | 47869 |
Tf_char | tf_age_y | 579 | 204 | 572 | 655 |
Tf_char | total_trees | 142 | 60 | 100 | 200 |
Tf_char | elevation | 80 | 51 | 32 | 121 |
Tf_char | lon | -1.79 | 1.11 | -2.13 | -1.16 |
Tf_char | lat | 53.00 | 1.39 | 52.36 | 53.32 |
Many indicators are highly correlated or cluster as shown in Figure 5 which orders pair-wise correlations of scaled (normalised) metrics by hierarchical cluster. Rainfall metrics cluster and are inversely correlated with temperature indicators. Gardens, built areas and roads form a separate cluster as do connectivity metrics, and vegetation/‘greenness’ indicators.
Gamma diversity
Results
Mean TF butterfly SR was 2.29 (survey sites = 42) and varied between 1 and 8. Taxon richness also varied between 1 and 13 (mean = 6.2, sites = 102) for pollinators and 1 to 10 (mean = 5.03, sites = 81) for ground dwelling invertebrates respectively.
As Figure 7 shows, TF butterfly richness is uncorrelated with TFb butterfly or insect SR.
Intrinsic TF variables were then fitted to butterfly SR using GLMM with a negative binomial error structure and TF as a random effect. The 10 models with the lowest AICc fitted with the dredge
function of the MuMIm
R package are shown in ?@tbl-butterfly-model (Bartoń (2023)). Each row of the table shows the coefficients of the explanatory variables - the number of surveys (n) is included in all 10 models, with mean age at time of survey (scaled) included in four. Survey month and weighted tree height are included in 2 candidate models.
Model selection can be difficult. It has been common practice in ecology to average models with with an AICc within 7 of the model of the lowest AICc but this has been criticised for leading to faulty inferences about relevant predictors (Galipaud et al. (2014); Walker (2017)).
An alternative is use penalised regression where predictors are removed
Ground dwelling invertebrates
GDM
Generalised dissimilarity models (GDM) were fitted to community matrices generated for each TF site for butterflies, pollinators and ground dwelling invertebrates to test the hypothesis that community composition changed as forest aged. Modelling followed the method set out by Mokany et al. (2022).
taxon | Important variables | All predictors |
---|---|---|
Butterflies | Geographic...1 | 0.00 |
Butterflies | shannon...2 | 0.28 |
Butterflies | mean_ht...3 | 0.54 |
Pollinators | Geographic...4 | 0.20 |
Pollinators | mean_ht...5 | 0.58 |
Pollinators | tf_age...6 | 0.28 |
Ground dwellers) | Geographic...7 | 0.00 |
Ground dwellers) | shannon...8 | 0.68 |
Ground dwellers) | mean_ht...9 | 0.66 |
Ground dwellers) | tf_age...10 | 0.00 |
Relationship between intrinsic tiny forest variables and tiny forest species, richness
Impacts of characteristics of surrounding area on tiny forest, biodiversity line Abiotic. Biotic
taxon | metric | estimate |
---|---|---|
Butterfly | gi_prop | 0.18352018 |
Butterfly | n | 0.03240214 |
Butterfly | lnk_y | 0.00093757 |
Butterfly | hedge_len | 0.00000651 |
Butterfly | watercourse | 0.00000115 |
Butterfly | wood_area_sum | 0.00000012 |
Butterfly | nc_y | -0.00009932 |
Butterfly | tf_rain_2021 | -0.00303056 |
Butterfly | perc_tree | -6.97509738 |
Ground-dwellers | lat | 0.02982828 |
Ground-dwellers | n | 0.01232032 |
Ground-dwellers | tf_age_y | 0.00014862 |
Pollinators | n | 0.04499600 |
Environmnental predictors of taxon richness
The results of glment
modelling are shown in Figure 11. For butterflies, green infrastructure, linear features (water courses and hedges), wooded areas, rainfall and connectivity metrics variables were found to be weakly positively associated with butterfly SR, whereas tree cover was strongly negatively predictive. For pollinators and ground-dwellers, SR was associated with the number of surveys, and increased with forest age and latitude for ground-dwellers.
Estimated SR for small areas based on random sampling
Estimated SR for small areas based on SAR
Sampling
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Butterfly richness estimated by sampling
Based on 300 (of 10,000) randomly sample 4Ha pseudo-controls, median butterfly richness was , with a percentile range of Butterfly diversity for TFs was 22 which is at the 95th centile of the distribution. Butterfly richness was highest in suburban areas approaching near saturation at 34 species. Richness in arable areas, improved grassland and deciduous woodland were lower but based on smaller samples.For a single 4Ha site the highest SR was in fen habitat (15 species), with arable (12), suburban (11), grassland (10) and woodland (8).