We found in two habitats, ridges (2015) and valleys (2016), in a Mediterranean mesic woodland ecosystem (Mt. Meron, Upper Galilee, northern Israel) evidence of lower day-butterfly-population indices (richness and abundance) in sites under cattle grazing, compared with ungrazed control sites. This is consistent with other studies that found a negative impact of grazing on butterfly communities (Börschig et al. 2013; Grill and Cleary 2003; Jugovic et al. 2013; Kruess and Tscharntke 2002; Schtickzella et al. 2007).
We found the woody-niche-affiliated butterflies to be more severely affected by grazing, in comparison with batha-patch-affiliated butterflies. This could be due to heavy cattle grazing on shrubs, vines (Schoenbaum et al. 2018), lower tree canopies and the understory Poaceae (grasses) plants, which are hosts for butterfly breeding (Schtickzella et al. 2007). The heavy grazing in the woods might be due to a lack of herbaceous pasture in the batha patches during the long Mediterranean dry season. This effect is supported by the findings of Kirk et al. (2019) in northern Tunisia, which showed severe damage to the woody community composition under moderate-to-high grazing pressure.
In the batha patches we found in the grazed sites (mainly on ridges), a lower abundance of butterfly species that breed on Brassicaceae, Lamiaceae and Poaceae (Tables 5, 6). This can be explained by damage incurred by cattle grazing to both nectar and breeding plants of Lamiaceae and Poaceae (Schtickzella et al. 2007). It is possible that some of the Asteraceae and the Fabaceae nectar and breeding plants (and, in valleys, Brassicaceae, as well) did not significantly suffer from grazing. These plants are the hosts of generalist (polyphagous) butterfly species, mainly the Pieridae (Tables 4, 7), which did not show decline in the grazing sites, and some that even increased (Tables 5, 6, 7, Fig. 6). The moderate damage for batha-patch-affiliated butterflies due to grazing corroborates previous studies from batha Mediterranean grassland ecosystems, which reported a diversity increase under a moderate grazing regime (Noy-Meir et al. 1989).
We conclude that monophagous and endangered butterfly species are more sensitive to cattle grazing than the oligophagous and polyphagous species are (Tables 4, 7). Similar findings have been reported from Morocco (Thomas and Mallorie 1985), Greece (Grill and Cleary 2003), and Italy (Scandurra et al. 2016). This may be the result of big mammals' influence on the vegetation, which increases evenness (less available ecological niches) and mainly damages the more specialist and sensitive butterfly species.
The oligophagous species Aricia agestis was the only endangered species whose population was significantly larger in the grazed site than in the control site – 57 versus 8 individuals in the valleys, respectively (Table 4, Fig. 6). This butterfly breeds on plant species of the Geraniaceae, which are palatable for cattle (personal knowledge). Geraniaceae were observed in the study area only as a minor vegetation feature and could not explain that intriguing effect. This warrants further research.
The common batha-patch polyphagous species Lampides boeticus, which was negatively affected by grazing, behaved almost "monophagously" in our study area. It breeds mainly on young branches of Spartium junceum (a bush, Fabaceae), which is eaten rapidly by the cattle.
We found heavier grazing damage on the ridges in 2015 (under winter–spring grazing regime) than in the valleys in 2016 (under summer–autumn grazing regime), in terms of both butterfly richness index (Figs. 1, 2, 5), and the abundance of the batha-affiliated butterfly species. On the ridge even butterfly populations that breed on increaser plants, which may benefit from grazing, still had lower indices than in the control. However, in the valleys some of these species had higher indices in the grazed sites (see also Briske 1996). Butterfly populations that breed on Brassicaceae were lower in the grazed site on the ridges, but did not decline, and were even higher in the valleys (Tables 5, 6). The same applies to Zerynthia spp. populations, which breed on the poisonous genera Aristolochia. The heavier grazing damage on the ridges, under a winter–spring grazing regime, could be attributed to that more intense management, compared with the valley grazing management of summer–autumn, with early season deferment.
The above difference between the ridges and the valleys habitats might explain the different effect there of cattle grazing on butterfly population evenness (Table 2) and diversity (Table 3). On the ridges we found high and similar evenness for the two managements, but greater diversity in the control. However, in the valleys we recorded in the control lower values of both diversity and evenness, and the evenness was there even lower than on the ridges. This lower evenness resulted from the higher number of endangered butterfly species there, most of which consist of very small populations (Table 4). The higher diversity of the control butterfly population on the ridges, compared with the grazing site, was a result of the control's higher richness combined with a similar evenness under the two managements. Nevertheless, in the valleys, the lower control's diversity resulted from a similar mean richness in the two sites but a lower evenness in the control. This is since Shannon diversity index is positively correlated with both evenness and richness indices.
We suggest that the significant changes in the butterfly populations under cattle grazing in the Mt. Meron region can be attributed to changes caused by grazing to their host and nectar plants (Pe'er and Settele 2008; Thomas and Mallorie 1985; Schtickzella et al. 2007). This is supported by the findings of a concomitant study done on the effect of cattle grazing on the herbs' communities (Oron and Lavi 2017), which was carried out on the same transect lines and years. In this research the herbaceous species richness was found to be lower in the grazed sites compared with the control; species diversity indices were lower under heavy winter–spring grazing management, compared with the less severe summer–autumn grazing regime; and the occurrence frequencies of the plant functional groups was found to differ clearly by management regime. All these changes would be expected to influence some of the butterfly populations. Another concomitant study, on the fungi in the woody patches of the same transects (Perelberg et al. 2016), also found a significant decrease in most of the ecological factors, which may emphasize the deep negative effect of cattle grazing on our research region.
The significantly lower butterfly population indices in the grazed sites, and almost total disappearance of the endangered species, under both heavy winter–spring grazing regime (on the ridges) and more moderate summer–autumn grazing (in the valleys), are consistent with Scandurra et al. (2016) and Schtickzella et al. (2007). However, other studies have reported significant advantages for butterflies under extensive grazing management compared with a no-grazing regime (Bartoňová et al. 2017; Munguira et al. 2017; Slancarova et al. 2015; Stefanescu et al. 2011). These contradicting findings might result from the ambiguity of the definition of "light-medium grazing management." Differences could also stem from the changing balance between the contradicting influences of grazing on plants and butterfly populations. Light-to-medium grazing may open the vegetation complex for more plant species (increase richness and diversity), but at the same time can damage or eliminate plant species of the butterflies' nectar and food complex.
The present research results demonstrate that cattle grazing, as conducted for two decades in the woodland ecosystem in northern Israel, has had significant harmful effects on the butterfly populations, apparently as a result of decreasing the habitat heterogeneity and reducing the food resources, and specifically by impairing plants. We hypothesized that in contrast to thousands of years of traditional goat grazing, the new cattle introduction in this area poses the potential for overgrazing damage. Further research is needed to support this assumption.