Turning small data into big rewards How to get critical information to prevent species loss

Plants and animals are disappearing at unprecedented rates due to threats caused by human modification and clearing of their habitats. Many governments are now investing in trying to reverse these declines before species are lost.

However, forecasting changes in communities of animals and plants under management is hindered by very little information on individual species’ responses to threats and their mitigation, as well as uncertainty in which species might benefit or suffer under alternative management strategies.

We are slowly learning the effects of some management actions on certain well-studied species. For example, in grazing or cropping landscapes where trees have been cleared, a number of woodland bird species such as the willie wagtail, grey fantail and many honeyeaters will most likely increase in a patch of remnant vegetation if we restore tree cover through revegetation or grazing exclusion.

L to R: willie wagtail, grey fantail, honeyeater.

We also know that other species might decline if their patch of vegetation is changed through restoration, because they prefer the current open conditions to more closed canopy woodland (e.g. the much-loved Bird of the Year, the Australian magpie, and parrots such as the eastern rosella).

Left: An Australian magpie having a meal. Right: An eastern rosella.

However, for many species, we have no idea whether conservation actions, such as planting more trees, will cause an increase or a decrease in their population as they are poorly studied or hard to detect.

Waiting for more information to be collected hampers our attempts to stop species declines and could even result in species’ extinctions if management actions are carried out too late or the wrong management actions are chosen.

Our study developed the first way of predicting community restructuring in landscapes where multiple threats act in concert.

Our approach enables managers to discover which species will benefit or decline under a selected management strategy, and how the entire community of associated species will change if one or more management actions are carried out in a degraded landscape.

The innovative approach combines dynamic models of species’ responses to independent and combined threat management actions with network analyses revealing species’ contributions to their co-occurrence network. Understanding what drives plants and animals to share (or not share) space and resources is critical for predicting and preventing biodiversity loss from the effects of anthropogenic change. Species “co-occurrence” (whereby some taxa coexist more often and some less often than expected by chance) results in webs or networks of links between species that are unique to each ecosystem.

Box Gum Grassy Woodlands in their natural state. Photo: Ayesha Tulloch.

We hypothesised that species who co-occur in the presence of threatening processes would share a similar response to the mitigation or elimination of those threats, as niche differences allow them to partition resources and maintain co-occurrence in the recovering landscape. Species that avoid one another in the threatened landscape are more likely to respond differently to threat elimination as their resource requirements (and hence threats) probably differ.

Using this information, we linked known responses to management by some common well-studied species (e.g. the willie wagtail) to unknown responses by rare or hard to find species who were able to survive with the known species (e.g. the brown treecreeper, a listed threatened species in NSW).

The brown treecreeper is endemic to eastern Australia

We applied our approach to evaluating potential changes under management in the complex and critically endangered ecological system of the Box Gum Grassy Woodland in eastern Australia, which is impacted by globally important threats of habitat loss, competitive displacement of woodland birds by the overabundant noisy miner and intensive livestock grazing.

Our study provides an important new foundation for combining species co-occurrence analysis with threat-impact modelling to discover how communities are likely to change under a management of cumulative anthropogenic threatening processes.

Natural Box Gum Grassy Woodland...

Cleared Box Gum Grassy Woodland...

Grazed Box Gum Grassy Woodland...

Our results reveal important relationships between a species’ role within its network of co-occurring organisms and its ability to be recovered by mitigating cumulative threatening processes.

First, we discover that species with more co-occurrence relationships are most likely to decline under cumulative threats.
In contrast, species resilient to threats tend to have more and stronger negative co-occurrences (where two species avoid one another rather than sharing resources) than vulnerable species. This implies that community structure is significantly altered by cumulative threats, due to loss of species with strong positive links and increased populations of species that are avoided by others.
As a consequence, we predict that threat mitigation will increase populations of birds with more connections to other birds, leading to higher network connectivity, whilst species with more negative associations (e.g. eastern rosellas and magpies) are more likely to decline.

Our study is unique in evaluating our predictions five years after management of the three threats; and what we found supported our models. Birds that co-occurred in the threatened landscape were more likely to respond in similar ways (e.g. both species increased when livestock grazing was reduced), and species with more links responded better than those with few links to other species. Birds that avoided one another in the threatened landscape were more likely to respond to management in different ways (e.g. one species increased when livestock were removed from a vegetation patch whilst the other declined).

Despite overwhelming evidence that most ecosystems are exposed to multiple co-occurring threats that need to be managed simultaneously to recover species, no studies have attempted to predict the likely outcomes of mitigating multiple threats on the entire community of species, information that is vital to effective management decisions.

Our paper shows that analyses of co-occurrence networks are crucial for informing decisions about threat management when there are uncertainties about which species might benefit versus suffer from a given action and not enough time or money to learn about every individual species’ response. By thinking not only about individual species but about how they share space and resources with others, we can ensure that management actions are chosen that benefit the most vulnerable species, and avoid actions that might lead to unintended declines.

Dr Ayesha Tulloch (CEED, ANU) and Dr Iadine Chades (CEED, CSIRO)

Read the research published in Nature

For more information: a.tulloch@uq.edu.au



Created with images by leardstateforest - "Aerials of Leard State Forest and surrounds." • AdaMacey - "Barbs gettin' rusty..." • PaulBalfe - "Little Grey Fantail" • sandid - "lewin's honeyeater meliphaga lewinii bird" • sandid - "magpie australian magpie hungry" • sharp_pics - "Eastern rosella" • recoverling - "qld deforestation" • sussexbirder - "Brown Treecreeper (Climacteris picumnus)" • leardstateforest - "Aerials of Leard State Forest and surrounds." • James Niland - "Noisy Miner Portrait" • blachswan - "Eastern Rosella"

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