Hello everyone!
In my last post, I discussed the direct effects acid deposition has on amphibians leading to mortality, development abnormalities, and shifting of community structure. I would like to continue from there and discuss the indirect effects acid deposition has on amphibians.
As I have previously discussed, we have seen how low pH on surface water has significant direct effects on eggs and larvae stages while not so much on the adults. The indirect effects on terrestrial habitats are more important for adults. Acid deposition can affect trees either directly or indirectly. The direct damage mechanism involves a progressive loss of foliage and discoloration of the remaining leaves. Sometimes, there is also evidence of death or distortion of roots (Antal & Puttonen, 2006). This deterioration may result in the eventual death of the tree. Besides direct damages, acid deposition can make a tree more vulnerable to other stresses. Branches and stem can suffer fungal, insect, mammal attack, increased evaporation as well as direct damage by wind and storms. Potentially the most serious effect is the destruction of forests which leads to deterioration and narrowing of habitats (Antal & Puttonen, 2006). There are thus several consequences of damaging forests on amphibians that I will discuss here based on the study by Antal & Puttonen, 2006:
#1 Increased warming:
As a result of foliage loss, an increased amount of sunlight is able to reach the forest floor leading to higher evaporation of surface water. To make matter worse, wind speeds within forests can increase and thus maintain high evaporation demand. This can lead to drying out of small ponds and wet surface areas which are important reproduction sites. As a result of foliage loss, shaded hiding places decreased. The warmer temperatures and increased evaporation can cause the sensitive outer layer of amphibians to desiccate more easily. With a reduced water body, they would have to resort to traveling further distances exposing themselves to many threats that reduce their fitness (Antal & Puttonen, 2006).
#2 Balks in the food chain:
During the larvae stages, they consume algae, other aquatic vegetal substrates, mud, seaweeds, and small animals. Shrinkage of such water bodies endangers food sources for these juveniles. Fortunately, most adults can consume a variety of prey and thus can tolerate such alteration. However, the altered environment can change the composition of predators which can negatively affect these amphibians populations (Antal & Puttonen, 2006).
#3 Difficulties in winter survival
To survive through winter, amphibians apply the method of suspended animation. Some amphibians burrow into the ground while some choose the mud layer of aquatic habitat. As temperature declines, the amphibian body temperature decreases. During suspended animation, body temperature decreases to 2-4°C, heartbeat declines to 10 %, and oxygen utilization declines to only 2 % of the normal. If you are interested to know more about how the Wood frog is able to freeze and thaw, do watch this video by Smithsonian Channel.
They also prefer soils of deciduous forests rather than conifers. Firstly, there is a significant thermal effect from the fallen dead leaves more so than the coniferous needles. Secondly, neutral or mildly alkaline soil condition is required as they produce alkaline mucus to keep the outer layer moist. Under acidic conditions of coniferous soil, this function can be impaired. Acid deposition results in reduced thermal cover due to reduced leaf litter and lower temperatures on the forest floor. Soil acidity has a negative impact on the distribution of terrestrial amphibians (Wyman & Hawksley-Lescault, 1987). As the normal functioning of the skin glandules is impaired, the uncertainty for winter survival becomes greater.
Acid deposition can affect amphibians both directly and indirectly. Forest serves as an important habitat for them. It is thus evident that the protection and restoration of these forests from acidification are imperative in conserving these species.
That brings me to the end of this post.
See you guys soon!
References
Antal, S. & Puttonen, P. (2006): The effects of acid rain on anurans and the possibilities of protection in Hungary, focusing on the challenges of forest management. North-Western Journal of Zoology 2(1): 47-58.
Wyman, R. L., & Hawksley-Lescault, D. S. (1987). Soil Acidity Affects Distribution, Behavior, and Physiology of the Salamader Plethodon Cinereus. Ecology, 68(6), 1819-1827. doi:10.2307/1939873
