Thread by @RewildingS

1/ Todays #rewildingscience paper examines how climate change interacts with other disturbances to alter functioning ecosystems in the Serengeti. It shows the joined up nature of ecosystems & trophic levels & challenges conservation to think at a landscape scale. #rewilding

2/ The paper focuses on 4 principles (1) interaction of environmental change with human-modified habitat; (2) slow change in the community; (3) fast change: rapid community shifts and stable states; and (4) other disturbances that override environmental change

3/ The study used road transects between 1997 and 2011 split between savanna and agricultural habitats along with historic literature to sample bird communities and monitored tree densities alongside this to investigate the relationship between tree stem density & bird diversity

4/ Rainfall is the main environmental driver in Serengeti with temperature being of lesser importance. Biological communities respond to changes in rainfall; if conditions become drier, communities will move towards wetter regions, and if wetter then the reverse will occur.

5/ The avifauna is a good example of this, however barriers present limiting factors. If conditions become wetter, the fauna that depends on trees cannot move to drier areas because the habitat changes from savanna (with trees) to open treeless grassland – trees cannot grow

6/ Conversely if conditions become drier, the native avifauna will move towards wetter areas that now are severely modified by agriculture. Trees are largely absent, native grasses are replaced by monocultures of domestic crops and shrubs become abundant along hedgerows

7/ Results showed the number of species in savanna were higher by a factor of two than in agriculture. For African wide species, East African species and Regional endemics there were significantly more species recorded in savannah than agriculture in each range category.

8/ The number of savanna species continued to increase as sample size increased, whereas the number of agricultural species was reaching an asymptote, indicating there would be even larger differences in number of species

9/ The study also found significantly more species in savanna than in agriculture at all trophic levels. Both herbivores and insectivores lost 14–15% of species in agriculture. While for vertebrate feeder richness, 38% of species disappeared in agriculture

10/ These results suggest that major changes in habitat cause animal communities to change. With local endemics (usual most habitat specific) the most impacted, with generalist african wide species the least

11/ This result implies that if climate change causes rainfall to decrease, birds will be forced to move westwards to stay in a region with the same rainfall. The consequence would be that some species would move into agricultural areas causing the loss of fragile species

12/ The results also show a greater proportion of species and individuals at the higher trophic levels are lost in the move to agriculture compared to those at the lower herbivore levels. This change in the trophic structure could result in more marked tropic cascades.

13/ The paper emphasises the loss of key functional species would have profound impacts on the entire system. For example the loss of insectivores recorded, would result in episodic insect outbreaks.

14/ Similarly, rodent-eating raptors respond to outbreaks of rodents. After outbreak events rodents remain at low numbers for intervening years due this response. However, in agriculture effectively all these raptor species disappear causing prolonged outbreaks of these 'pests'

15/ In Serengeti there has been a more general spread of species due to climate change. These illustrate that changes in community structure as a result of ecosystem disturbances, one of which is environmental change, has led to changes in trophic dynamics

16/ Next the paper highlghts the role avifauna plays in determining plant community structure. Change in this fauna due to disturbance, results in a change in plant community state.

17/ The study found that as tree density and canopy cover declined, the number of forest bird species declined from 26 species in 1966 to 3 in 2006. This decline in species occurred primarily when gaps in the canopy allowed grasses and herbs to encroach on the forest floor

18/ The paper highlights the stable interaction of birds, fruits, germination and seedling recruitment in undisturbed forest. Birds protect seeds, through feeding, from beetle attack, indirectly improving the germination of seeds and ultimately regeneration of forest tree species

19/ The disappearance of this stability through disturbance causes the forest to unravel through a positive feedback loop. The drop in frugivorous bird feeding leads to bruchid beetle attack on seeds & a drop in germination rate & seedling recruitment to the forest tree community

20/ Once begun, the process leads to forest fragmentation and progressive unravelling in the biotic community until it disappears. The loss of a particular suite of bird species had an unexpected and catastrophic effect on the viability of the forest ecosystem as a whole.

21/ This slow change can also be influenced by other disturbance factors such as disease, which have the potential to alter both wildlife dynamics and human driven processes such as burning and hunting.

22/ The paper concludes with four lessons: (1) habitat modification through agriculture limits endemic species and top trophic levels. The loss of rare species and top trophic levels should be a big concern for conservation

23/ (2) Disease & hunting cause slow change in the species complex. This can alter community dynamics depending on which species enter or leave. (3) Habitat fragmentation or decay can cause slow change. At a threshold there may then be rapid change in the species composition

24/ Finally the paper states that accepting systems change requires a new approach to conservation. Within protected areas, new boundaries or new areas will be required. Outside them, #rewilding is required to support more biodiversity.

25/ I really liked this paper, it really emphasises the joined up nature of ecosystems and the need to avoid short-term thinking, as these profound changes are often slow. More than anything it shows that conservation thinking needs to be at a landscape level #rewildingscience

26/26 The paper can be found here: researchgate.net/publication/26…

It is well worth a read and the lessons here certainly underpin a lot of what proponents of rewilding suggest.

#rewildingscience #rewilding #paperreview