Though desert tortoises are well adapted to arid habitats, and adults can survive a year without access to water, they rely heavily on moisture in the vegetation consumed in spring, when they surface from their hibernal dormancy. The loss of native plants to grazing livestock and invasive plant species, then, may lessen the tortoise’s resistance to pathogens, though the tortoises do also dig precipitation basins in the soil and linger near one when rain is impending.
Q1:it's a X and Y structure. What's the XY?
X=The loss of native plants
Y=invasive plant species
or
X=grazing livestock
Y=invasive plant species
Q2:I don't really the meaning of "The loss of native plants to grazing livestock and invasive plant species", can you help me to rephrase it?
Thank you very much!