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Home arrow Environment arrow Bats in the Anthropocene: Conservation of Bats in a Changing World

Effects of Agricultural Intensity on Bat Assemblage Structure, Behavior, and Ecology

We found 70 studies addressing the effects of habitat conversion or management on the assemblage structure, behavior, or ecology of bats. Fifty-two studies assessed bats in both natural and agricultural areas. Twenty-two studies (42 %) demonstrated negative effects of habitat conversion, twelve (23 %) showed variable responses (e.g., only some species or ensembles declined, different agricultural systems were associated with different effects), twelve (23 %) showed increased richness, activity, or abundance in agricultural areas, and six (12 %) showed little or no difference between agricultural and natural areas. Forty-five studies addressed some aspect of agricultural intensification, with 38 of these (84 %) documenting a negative effect of intensification on bats, four showing variable or neutral (9 %) responses, while three studies (7 %) documented increases in bat richness, abundance, or activity in more intensive systems.

Response variables differ in response to habitat conversion and agricultural intensification (Fig. 6.2, Table 6.2), with measures of species richness showing no significant change between treatments. In contrast, measures of relative activity and abundance show stronger responses (Fig. 6.2). Agroforestry systems are more structurally similar to the original non-anthropogenic land uses, making them less intensive than annual crops dominated by one plant species or pasture systems lacking structural complexity. This relationship presumably explains why agricultural systems that incorporate trees and other large woody perennials on farms and throughout the agricultural landscape have little effect on bat activity and abundance (Fig. 6.2). Agroforestry systems appear to mitigate negative effects on bat assemblages in cases of both habitat conversion and agricultural intensification (Table 6.2).

Several studies have considered the effects of agricultural management at landscape scales versus focusing exclusively on farm-level management practices (Estrada et al. 1993; Ekman and de Jong 1996; Verboom and Huitema 1997; Numa et al. 2005; Faria et al. 2006, 2007; Faria and Baumgarten 2007; FuentesMontemayor et al. 2011; Boughey et al. 2011; Maas et al. 2013). Within agricultural areas, bat activity increases with proximity to natural areas (Estrada et al. 1993; Verboom and Huitema 1997; Boughey et al. 2011) and in less fragmented landscapes (Fuentes-Montemayor et al. 2011; Frey-Ehrenbold et al. 2013) or in landscapes with more natural elements such as hedgerows and woodlots (Verboom and Huitema 1997).

Agricultural areas also serve as matrix habitat connecting fragmented nonanthropogenic habitats. Although one study has suggested that landscapes dominated by crops and open fields have a stronger negative influence on bats than water (Ekman and de Jong 1996), a recent analysis of bat responses to isolation on islands versus in forest fragments embedded in agricultural matrix suggests that the anthropogenic matrix is more permeable than water matrix (Mendenhall et al.

Fig. 6.2 Mean effect size (log odds ratio, circles) ±95 % CI of relative abundance and activity (left) and species richness (right) of habitat conversion versus agricultural intensification (top row), and of contrasts (both habitat conversion and agricultural intensification) with and without agroforestry systems (bottom row). Positive effect sizes indicate reductions in relative abundance and activity or species richness in response to habitat conversion and intensification

2014). Thus, agricultural intensification at the landscape level should make the matrix less permeable due to the reduction of natural resources and structural elements such as trees, affecting not only the persistence of bats in fragmented landscapes, but also the degree to which bat assemblages show a negative response to agriculture. A few investigations have confirmed such interactions between farmand landscape-level intensification: Intensification in cacao matrices in Brazil (Faria et al. 2006, 2007; Faria and Baumgarten 2007) and coffee matrices in Colombia (Numa et al. 2005) resulted in reductions in the species richness and abundance of bats in diverse shade agroforests relative to forest fragments. In Europe, effects of landscape management on bat assemblage structure and ecology in temperate landscapes dedicated to the production of annual crops remain largely unexplored compared to the extensive information available at the field and farm scales.

Table 6.2 Effects of latitudinal zone and agroforestry systems on effect size (log odds ratio) for two response variable types under habitat conversion and agricultural intensification

Response variable

Land change type

Model

AIC

χ2

P

Abundance/ activity

Habitat conversion

Effect

size ~ (Method) + (Continent)

60.7

Effect size ~ Agroforestry + (Met hod) + (Continent)

49.7

13.00

<0.001

Effect size ~ Latitude + (Method)

+ (Continent)

62.0

0.00

1.000

Effect size ~ Agroforestry + Latitu de + (Method) + (Continent)

51.9

12.15

<0.001

Intensification

Effect

size ~ (Method) + (Continent)

52.4

Effect size ~ Agroforestry + (Met hod) + (Continent)

49.2

5.22

0.022

Effect size ~ Latitude + (Method)

+ (Continent)

53.6

0.00

1.000

Effect size ~ Agroforestry + Latitu de + (Method) + (Continent)

50.6

4.923

0.026

Species richness

Habitat conversion

Effect

size ~ (Method) + (Continent)

20.7

Effect size ~ Agroforestry + (Meth od) + (Continent)

21.7

0.99

0.319

Effect size ~ Latitude + (Method)

+ (Continent)

24.0

0.00

1.000

Effect size ~ Agroforestry + Latitu de + (Method) + (Continent)

24.1

1.82

0.178

Intensification

Effect

size ~ (Method) + (Continent)

22.9

Effect size ~ Agroforestry + (Meth od) + (Continent)

24.4

0.54

0.460

Effect size ~ Latitude + (Method)

+ (Continent)

26.3

0.06

0.806

Effect size ~ Agroforestry + Latitu de + (Method) + (Continent)

27.0

1.34

0.248

Parentheses indicate random effects, and bold text indicates best fitting model based on AIC value

 
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